# 4 stroke 60/40 on 1648 River Rhino with UHMW??



## rotus623

Hey guys I was working on a jet boat project and ended up selling my motor and going to sell the boat separately.
I realized that I was going to spend about 7-8k total plus lots of time and I have found some nice rigs up and down the east coast for around the same price.

Anyways, I found a 1648 river rhino with 4 stroke 60/40 merc and uhmw on the bottom, up in Pennsylvania. The boat is .125 gauge all around. Anyways, as I am thinking about it I feel like this thing might be named the "sea slug" and that may be why the guy is selling it. I am thinking with the weight of the 4 stroke and UHMW, and narrow bottom of 48", we have a sluggish combo. What do you guys think?


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## LarryMc

Did you see this Rhino with a 2 stroke 60/40 made by James River Jets? 
https://richmond.craigslist.org/boa/5949567631.html
I fished a couple of times with a guy that had one almost identical with the one shown here. It was a real nice boat with lots of storage and Stick Steering which I really like. It ran pretty good, although not quite as fast or as quick to get on plane as my Lowe when I had the 2 stroke 60/40 on it. He had UHMW put on it after he had owned it for a while. He told me that the UHMW really hurt the performance, but I never fished in it after the UHMW was installed so I can't say how much performance loss there actually was. 

I wouldn't want to speculate why the guy with the boat you described wants to sell it, but judging from my experience with re-powering my boat with a Mercury 4 stroke 40 jet, I would guess that the performance of his boat with the combination of a 4 stroke 40 jet, a .i25" hull and an UHMW bottom would leave a lot to be desired. That said, the only way to actually know what the boat will do is to drive it, so that would be my suggestion before deciding whether or not to buy it.


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## rotus623

Thanks for the in depth reply. Hull is similar to what you posted, but with a 4 stroke engine. I am wondering, what did you notice performance wise when you moved from a 2strok to 4 stroke 60/40?


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## LarryMc

I lost 2-3 MPH of top speed running in still water and the hole shot really suffered after the switch. I would estimate that it takes close to double the distance to get on plane with the 4 stroke as it did the 2 stroke. The lower top speed doesn't bother me nearly as much as the increased distance required to get on plane. There are times when running a jet that you need to get on plane quickly in shallow water in order to avoid hitting bottom with the jet foot. The 4 stroke just doesn't cut it in a situation like that.

Check out the thread link below for a more comprehensive discussion of the difference between the two motors. 
https://www.tinboats.net/forum/viewtopic.php?f=85&t=41247


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## rotus623

LarryMc said:


> I would estimate that it takes close to double the distance to get on plane with the 4 stroke as it did the 2 stroke.



WOW!! See I hear rumors about this all the time, but it's nice to hear it straight from the horses mouth. I do love the idling properties of 4 strokes, and how quiet they are when trolling around. I do a lot of idling where I fish, and much of the time I am running through new places. BUT, that being said there are places where a fast hole shot is required. Especially in late August early September when the water gets real low.

So on a narrow bottom (48") with UHMW, .125 hull, and 4 stroke engine, I think I am starting to see why this guy is selling this rig. Probably really is a "sea slug."


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## rotus623

Ok fellas so I took her for a test run today. Checked compression and we were looking at 180psi across the bboard cold. She fired right up and idled perfectly. Looked great under the hood and had a good amount of power.

So the boat is .125 all around. It has 1/8" UHMW (30lbsof weight according to Jim Starkey) and a tunnel. Three batteries and a full 12 gallon fuel tank. One 200lb guy and one 150lb guy. Honestly the hole shot was pretty good all things considered. She got on plane in about 2 boat lengths. Stayed on plane easily. There were two issues that I noticed. One was top speed upriver was only 23 and down river 25. The other issue is that the tail end rode heavy. Ran maybe 10" deep in the back on plane. I was hoping for much better than that.

The start battery and gas tank was in the rear, about 120lbs total. The 4 stroke motor weighs 267lbs.

I was thinking of starting by moving the tank and battery up. If that doesn't work maybe I need to sell the motor and get a 90/65 2 stroke? The motor is clean and I'm sure I can get $4000-4500 for it in a couple Weeks. 

Price was great!! So I did purchase it. What you guys think I should do to get better performance?


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## rotus623




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## JL8Jeff

That speed might be right for the 4 stroke, that boat looks kind of heavy compared to my 1652 Lowe.


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## stinkfoot

I would definitely try shifting some weight around to get the boat more level. Makes a huge difference on my 16 foot jet jon.


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## rotus623

Cool man, I will try shifting some weight. I also need to inspect my impeller clearance.


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## rotus623

@JL8Jeff hey bud was wondering. How did you know you needed to wedge your transom? I feel like tucking the foot in will help some, although the transom angle is built
For yet motors on the rhino jets.


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## LarryMc

With a bow mount trolling motor, two TM batteries up front and the driver also up front, I doubt that the weight distribution is very far off. How does it float when not under power? 

Have any idea what the Wide Open Throttle RPM is?


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## rotus623

Hmmm,

Don't have a tach on it yet, but I have a video I will try and post. Motor sounds about right, maybe around 5000rpms or so. 

It floats really well while not under power, maybe 5-6".


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## rotus623

Here's a vid of her runnin to give you an idea of WOT rpms.

https://m.youtube.com/watch?feature=youtu.be&v=SXL5DXoyLSY


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## LarryMc

rotus623 said:


> Hmmm,
> 
> Don't have a tach on it yet, but I have a video I will try and post. Motor sounds about right, maybe around 5000rpms or so.
> 
> It floats really well while not under power, maybe 5-6".



Does it float level from stern to bow? If so, your weight distribution is good. A jet boat that runs with the stern low and the bow high is often a sign that the boat is under-powered. I honestly doubt, given the construction of the boat that you have, that you will be able to improve the performance with the 4 stroke Mercury 40 Jet. If you do succeed in getting the bow to run lower, it will probably just plow through the water and will actually reduce your top speed.


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## rotus623

Not sure how she looks in the water at rest, but the waterline suggests it is relatively balanced. I don't feel like the boat has its nose in the sky when it is running, just that the tail end sets too low. It has plenty of power to get on plane, and you can throttle back 1/4 or so and it will stay planed out. This is one heavy boat for sure though


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## LarryMc

A suggestion that _might_ help raise the stern. Try bending the trim tabs down. The one on the starboard side in the photo of your motor looks like it's bent up.


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## rotus623

So I think I hit the jackpot in one aspect. I measured the thickness of thenbottom and its .190 gauge!! Man this thing is a tank!! Just adding to more reasons why the 60/40 is an ad choice on her, not that it won't do the job 

Anyways, I looked at the "trim" tabs oming off the back and they aren't bent at all. The issue is that they are very thick and are welded to the water drains and the tracking channel underneath. I think trying to bend these will be a lost cause and nearly impossible short of cutting a notch in them on the outer side of the tracking channel. That thing is covered with uhmw too!!


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## stinkfoot

You could bend some thinner aluminum and bolt it on to what you have though.


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## rotus623

That's a great idea stinkfoot!!! That will allow me to just take em off if i don't like em.
Trim tabs really helped my other boat. It may be worth a shot!


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## JL8Jeff

rotus623 said:


> @JL8Jeff hey bud was wondering. How did you know you needed to wedge your transom? I feel like tucking the foot in will help some, although the transom angle is built
> For yet motors on the rhino jets.



My boat would start to porpoise at higher speeds so I put the wedges on and it fixed the porpoising.


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## LarryMc

I can see that they aren't bent with the new photos that you posted. Stinkfoot's suggestion might be worth a try.


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## stinkfoot

Might be possible to fabricate something that was adjustable rather than buying actual trim tabs....


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## rotus623

Yea I don't want to put actual trim tabs on because they will dig a little deeper down than I want. I think a bendable set of removable aluminum plates bolted in would do well.

I am having a hard time still, understanding how this boat that is designed to run in inches of water is running in 10"+. It would seem something extremely fundamentally wrong is going on. I need to inspect the liner clearance also. I also wonder if adding an extra 50-60lbs for a 90/65 2 stroke jet will help or hurt me. 

I also think that the 48" bottom is part of the culprit. Would float pods help at all? I know they are more for static displacement...... wheels are just turning here guys. I have set up a lot of boats but not many jets with marginal power. Transom tag says max motor is 90/65 jet.


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## stinkfoot

I thought about float pods for your problem. I have a buddy with a Wooldridge with a 115/80 and another with a G3 with a 60/40. I noticed when the Wooly slows down so the G3 can keep up his ass sits really deep and bow way up even though he is still planing....


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## rotus623

That's good info! That backs up what Larry was saying earlier. Just because you are on plane doesn't mean you have enough oomph to get that tail end up and out of the water. These slick bottoms have a lot of drag due to surface tension. Which also adds to the sluggishness.

My last boat was the same way. Was a 16' all welded jon and had a 25/20 tiller steer on the back. Got in plane pretty well but tail end just set low. I guarantee that light boat would have loved a 50/35 on it. But the hull wasn't solid enough for me. I just don't want to split a hull wide open and hurt someone. I don't know the upper James as well as I would like to so I like the idea of a tank to learn.


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## stinkfoot

See you posted on meanchicken. Probably the best place to get advice. I am arrgh! on there....


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## rotus623

Ok bud cool. Yea I know you and Jeff are on there, possibly Larry too? I am just scrounging for ideas before I yank this engine off. I'd hate to do it if I don't need to.


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## LarryMc

I'm on meanchicken now. :mrgreen: Didn't even know it existed until I saw stinkfoot's post a few minutes ago.


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## stinkfoot

LarryMc said:


> I'm on meanchicken now. :mrgreen: Didn't even know it existed until I saw stinkfoot's post a few minutes ago.



People from all over on there. Some interesting stuff to read. I like it when the NZ boys show off their stuff and there was an awesome jet build from Africa. Funnily enough it was someone on Meanchicken that put me on to Tinboats..... 8)


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## rotus623

Them boys over there make me want to scrap the outboard jet deal and go inboard jet


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## stinkfoot

https://www.jetstreamboats.com/ This guy is just up the road from me. If you can weld you can pick up a kit for around US$2K.


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## rotus623

Man those things are sweet!! You could go anywhere in them!


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## stinkfoot

rotus623 said:


> Man those things are sweet!! You could go anywhere in them!


 There are a couple of build threads on meanchicken. I believe the owner is also on there.


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## handyandy

The tunnel is slowing you down for sure makes the back end/stern draft more water. It helps protect the shoe some but I always question how much good they do if they get the shoe 2-3" higher but makes the stern sit 1-3" lower causing more drag and reduced speed. The only way you will get much better performance with the combo is for starters make sure everything in the engine is up to snuff, like how sharp is the impeller, whats the impeller to liner clearance, what rpm is it running wide open. They changed the stainless impeller design that mercury sells those engines with now to help the four strokes get in there peak rpm range if you have the old style impeller it's better suited to two strokes, I'd be glad to buy it off you if you have the old style. Heck I'd buy you a new style one for a old style if it's in good shape. So check your wide open rpm. You could ;sand and polish the impeller, intake, and pump to for some performance gains but it's a lot of work for little gain that ultimately can get ruined by ingesting some gravel on accident. With that said sanding out real rough spots and getting everything at least smoother than the factories rather rough castings helps some. Three do anything you can to lighten the boat up. If you can get away with one trolling motor battery than lose a battery, maybe the flotation foam is water logged and needs to be replaced. Losing weight out of the boat will give you the most gain. Adding some flotation pods to the back won't help top speed but could help hole shot and resting draft. Ultimately pods and a 90/65 would give you the best results. At the end of the day it seems like flat tunnel hulls in this size range 16-18ft are just hard to make fast equivalent flat bottoms just run faster cause they don't have as much drag.


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## rotus623

Thanks for the in depth reply.

Yea those tunnels really up the drag and cut back on speed, that's for sure. That's the way they do it in the James though. I, personally,am happy sacrificing some speed/performance for the protection of a jet tunnel and UHMW plastic.(I am not getting snippy, just being honest) I split an .080 gauge hull right down the middle in april last year. I have also smacked the living tar out of my foot idling around and even drifting (last motor was not power trim.) Running new spots on the river can be a dangerous feat!! The ironic part is that you want to run it slowly to learn it, but can't because you are drafting too much water while at idle.

As far as impellers go, this one actually looks so clean I questioned if it was new!! I am going to inspect the liner clearance, as I suspect that the clearance may be too great. The guy who had the boat before me put in a new waterpump, and I doubt he tried moving the washers around. I will pull it in the next few days and get you a part number and take some pics. If you like what you see, I will take you up on your offer, and will gladly trade the old style for a new style. (The motor is an '07, so not sure when they changed the impellers over.)

Here is a video of a tunnel rhino running with a small tohatsu jet. I am pretty sure this looks very similar to how my hull looks while under way. https://www.youtube.com/watch?v=T1BKaexw7kc


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## rotus623

Oh, also, I called specialty mfg, and talked to the lady up front. She has always been very helpful to me. Anyways, I told her what pump I had on my rig (AGL-44) and she told me that the impeller was exactly the same as the 60/40 2 stroke, a 6 7/8" 3 blade. I have heard that some motors use a different impeller for 4s and 2s, but why wouldn't she know if this was the case? Seems strange....


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## LarryMc

It sounds like your motor has been converted from a prop to a jet. The AGL-44 is a unit designed to convert a long (20") shaft prop lower 4 stroke 60 HP motor to a 60/40 jet. It comes with an aluminum impeller that is the same as the one on the 2 stroke kits that Outboard jets sell. The aluminum impeller is part # 106.23. You should take yours off and see what the number is. The stainless factory impeller is part # 855708T60.

The pump on my motor, a factory jet manufactured in 2016, is an AGM. It came with a stainless 3 bladed impeller which has the trailing edge cut back to allow the 4 strokes to rev up a little higher than they will with the 2 stroke stainless impeller which has not been cut back.


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## rotus623

Man you guys are really on the ball here.

So, the motor serial number brings us to a 60hp EFI. No jet under parts breakdown. Plus the sticker said 60 on the cowling. So the motor has certainly been converted. Here's the fun part. The serial number on the pump is an AG, which was the same one on my short shaft 2 stroke 60/40. So I am guessing the guy who converted this just changed out the driveshaft for a 20".

All that being discovered, I am nearly positive that my impeller is the old 2 stroke style. (I guess that means it's aluminum?) how many rpms does one typically gain by moving to the stainless back cut impeller? What do one of those bad boys run new?


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## rotus623

Now what I am wondering is if the 2 stroke pump is hindering my performance. It looks like the liner on the 4 stroke is much smaller, and the foot is smaller also.


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## LarryMc

You should check your impeller so that you will know for sure what you have. The aluminum 6 7/8 has the part number 10623 stamped on the lower end. The stainless has the part number 855708T60 cast on the inside of the upper end. Whoever converted the motor may have already swapped a stainless for the aluminum. You won't know until you look at it.

I have tested all three types of impeller in my motor trying to get the best performance. In my boat running in still water, the aluminum and stainless 2S impellers both run 4900-5000 RPM with 23-24 MPH. The cutback stainless 4S impeller runs 5100-5200 RPM and 25-26 MPH. The 2S impellers gave a little better holeshot but less max speed. As you can see, for practical purposes, there is not a lot of difference. At least, as far as my boat and motor are concerned.

Both the Stainless 2S & 4S impellers use the same part number, so you have to look at them to tell the difference.
The first photo below is the 4 stroke impeller alongside the 2 stroke impeller (4S on the left). The second photo is a closeup of the 4 stroke impeller


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## LarryMc

rotus623 said:


> Now what I am wondering is if the 2 stroke pump is hindering my performance. It looks like the liner on the 4 stroke is much smaller, and the foot is smaller also.



There is no difference in the size of the intake for the AG & AGM pumps. The AG pumps used on the Mercury factory 2S jets used a bolt-in liner while the AGM use a flanged drop-in liner. That may be why they look different to you.


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## stinkfoot

Your link is broken, Larry. Rotus263, I would strongly advise you to call Brian at Outboard Jets. He is very helpful and knowledgeable even with obsolete old crap they don't make any more like I have. He went out of his way to help me even though there was little to no prospect of him selling me much more than a shift kit.


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## LarryMc

Got it!


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## rotus623

Wow Larry, thanks. It is great to have all your time and test data as a resource.

So I pulled the impeller tonight. First thing I did was take the grates out and measure impeller clearance. Last guy who put it on had it shifted to one side and I had close to .400 clearance on one end, and .300 on the other. I took the impeller out, sanded it up to clean up the castings, and dressed the leading edges. I could NOT for the life of me find any numbers on this thing at all, but from your pics, I can surely tell it is the 2s. Plus I know it is aluminum because of the color and the filings.

I ended up straightening out my grates, chiseling one side of each of them, and moving 2 shims up and setting my impeller clearance to .015 all around. I feel like this will make a difference for sure!!

At this point I think I should give her a run and if I'm still not satisfied maybe look for an4s impeller. What did that run ya Larry?


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## stinkfoot

So you didn't go with the SS one, Larry?


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## LarryMc

stinkfoot said:


> So you didn't go with the SS one, Larry?



Right now I am running the 2S stainless impeller that was in my old 2S motor. I'll probably go back to the 4S stainless that came with my new motor for the little extra speed, though. I'm also thinking about installing a set of Nauticus Smart Tabs to try improving the hole shot 

*rotus623*: As you have already determined even though you didn't find a part number, the impeller in your motor is aluminum. The aluminum ones use a different key than the SS ones. The SS impellers use a square key. .

I didn't buy the 4S SS impeller, it came in my motor. Buying an impeller could be complicated since the part numbers (855708T60) are the same on both the 2S & 4S. The 2S in my photo was bought in June, 2014 from https://mercuryperformance.com/index.php for around $320 including shipping. But I don't know which type you would get now if you bought one using that part number. You can also find them on eBay for around $330. Jet Doctor has the same impeller for $410, probably close to $450 by the time you paid shipping. A dealer would likely charge you about the same as the Jet Dr, but at least you could look at before buying it and see which type you actually have.


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## rotus623

Cool man thanks! I think now that I have fixed my impeller clearance issue, dressed the impeller, straightened and cleaned up and chiseled the intake grates I will take her up the river alone and see how she rides. Certainly don't want to sacrifice what holeshot that I do have in this 4 stroke for a few MPH up top. I am going to bring two 80lb. bags of concrete and play with the weight (of another person) and see how it changes the dynamics of the boat. If that 160lbs. turns her into a slug, I think I will know what my next move is.............


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## LarryMc

Probably a good plan. Judging from my experience and the experiences of a few other posters on this site, I don't think changing impellers is going to help you all that much.


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## rotus623

Thanks a lot man!! Hopefully I can get her out for a few hours this friday and make some test runs.


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## handyandy

Lary if you decide to sell that 2s SS impeller I'll buy lol. Sorry I forgot to reply to you about the aluminum one you have. Any ways on the topic I think shimming will help you. Only thing I'd suggest when dressing the impeller I would sharpen the part that faces the ground when it's installed in the engine I always sharpen the what is the top side of the leading edges when it's installed. Seems like to me the impeller is able to get more bite in the water that way. As far as all the pump AG series pumps are all the same be it 2s or 4s they changed the shoes later on late 90's or early 2000's the drop in flanged liner type intake shoes. But the shoes can be interchanged on old and new pumps. I know because I have a older aluminum intake that uses a bolt in none flanged liner, and one of the rockproof UHMW intakes that uses a flanged drop in liner. They both work on my older AG 2s pump. The pump housing is the same. I got my pump used it had a long shaft drive shaft in it my motor is a short I just ordered a new drive shaft and swapped it. I could swap in a 4s long drive shaft and it would work on your 4s. Let us know how it does now once you get a chance to run it. I understand on the tunnel and the hull you run. For me my preference is a stout flat bottom currently I run a 15ft excel flat bottom it's heavy as well being a .125 thick hull all around no UHMW though on the bottom this is with a old 1993 2s merc up river just me fishing gear it can run 28-29, add a person it goes to 27-28, three guys and duck hunting gear so loaded down it does 25-27 takes a little while to get on step though. After goose season is out I have a 70hp evinrude 3cyl with a jet I'm going to swap to and add pods to the back.


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## rotus623

handyandy said:


> Lary if you decide to sell that 2s SS impeller I'll buy lol. Sorry I forgot to reply to you about the aluminum one you have. Any ways on the topic I think shimming will help you. Only thing I'd suggest when dressing the impeller I would sharpen the part that faces the ground when it's installed in the engine I always sharpen the what is the top side of the leading edges when it's installed. Seems like to me the impeller is able to get more bite in the water that way. As far as all the pump AG series pumps are all the same be it 2s or 4s they changed the shoes later on late 90's or early 2000's the drop in flanged liner type intake shoes. But the shoes can be interchanged on old and new pumps. I know because I have a older aluminum intake that uses a bolt in none flanged liner, and one of the rockproof UHMW intakes that uses a flanged drop in liner. They both work on my older AG 2s pump. The pump housing is the same. I got my pump used it had a long shaft drive shaft in it my motor is a short I just ordered a new drive shaft and swapped it. I could swap in a 4s long drive shaft and it would work on your 4s. Let us know how it does now once you get a chance to run it. I understand on the tunnel and the hull you run. For me my preference is a stout flat bottom currently I run a 15ft excel flat bottom it's heavy as well being a .125 thick hull all around no UHMW though on the bottom this is with a old 1993 2s merc up river just me fishing gear it can run 28-29, add a person it goes to 27-28, three guys and duck hunting gear so loaded down it does 25-27 takes a little while to get on step though. After goose season is out I have a 70hp evinrude 3cyl with a jet I'm going to swap to and add pods to the back.



Thanks a lot for the info on the AG pump, that makes me feel better. I didn't sharpen the other side of the impeller, but if I have to pull it again I surely will give it a shot.

I think a stout boat with no tunnel will give ya some better performance than the jet, for sure. Tunnel seems to suck the tail end down some. They say pods don't help while on plane, but I think if you put the right ones on they would work like trim tabs. I personally have rock ledges that I would like to get over top, and the lack of jet foot hanging down as well as UHMW covered chines will definitely help with that (hopefully). Lots of rock ledges in the James and the only way around some of em is up and over. Run in nose high and let her lever herself over :shock:


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## handyandy

where on the james do you fish I was in Fort lee for four months in 2014 over the spring and summer. Didn't have my jet on the boat then so ran it with a prop and jack plate as best I could got around pretty well for what it was. Floated it a number of times in my kayak I fished below the falls a lot for cat fish and above I put in all over the place from I think scottsville was the town on down.


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## rotus623

That's awesome Andy, those are the exact waters I Run. We fish out of scottsville, Columbia, maidens, howardsville etc. I also fish Watkins landing and ancarrows with the jet. 

I also fish way down the James into Richmond for big blue catfish. Thats when I take the big boat out. For there and lake Anna stripers. Basically I am all over the map in his area depending on what time of year it is.


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## handyandy

I fished the apomatox river not sure on spelling near petersburg a lot when I was there since it was almost next door to the base. You couldn't really boat it I tried kayaking it a few times but in high water you got whit water, in low water those spots required dragging. There was a trail that followed the river most the way from petersburg up to the damn that formed some lake can't remember the name, but I'd ride my mountain bike with a milk crate I put on it with rod holder pipes up and down the trail to get to all the holes away from all the idiots of petersburg caught some good smallmouth in there. Pulled one just shy of 20" out from the apomatox. Had some good ones on the James. Caught quiet a few cats but never did get any monster blues biggest one was just shy of 20lbs if wasn't for that area being so urban, and having such weird water way laws on duck hunting the lower james I would try and move there. I'll have to be back at Fort lee for a month for some training possibly this spring summer, definitely next summer. When I go back there I will have my boat in tow, and will fish the upper james more smallies now that I have a jet. Will have to get in touch with you when I'm in that area.


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## rotus623

Yea bud gimme a shout for sure!! I put in at Hopewell a lot. That is right where the Appomattox comes into the James. I fish big stripers down that way in April-May.


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## rotus623

Ok guys did some test runs today. Brought 4 80lb bags of concrete to play around with weight. Took the two deep cycle batteries out of the bow.

With just me, trolling motor, start battery and 8 gallons of fuel she did good. Got on plane well (maybe 1.5 boat lengths) and ran 24.5 on the gps. 

With 160lbs in the rear seat area she didn't seem to take any longer to get on plane, and mostly felt comfortable. Ran 23.5 per gps.

With 160lbs of dead weight in the bow(simulating trolling motor batteries and gear) and 160lbs in the rear seat area, she ran 22.5. Felt a little slower to plane. Handled the load pretty well but definitely sat a little lower in the water when running.

Still not sure how much water she drafts to plane but I think it is much less than I thought.Here is the issue I am having: when hitting waves there are no issues. When getting on plane she wants to cavitate if I gun it. If I ease it into wot it's not as bad. It also will cavitate when the water has lit chop and while turning hard. Do you guys think those "water wings" on the foot will get rid of this?


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## LarryMc

The fins will help a lot on a non-tunnel jet to reduce cavitation. I'm not sure about a tunnel boat, though. Given that a tunnel is designed to force water into the intake and the fins are also designed for the same thing, I kind of doubt it. I've had them on my boat a few times but they usually don't last long (at least for me) on a non-tunnel boat because they lower the amount of clearance that you have on the front edge of the intake. That wouldn't be a problem on a tunnel boat, though. 
They will improve the steering on a jet if that matters to you. I know that the stern on flat bottom jets is bad to slide around on turns. My Lowe also slides quite a bit on turns and when I had the fins on, they helped to reduce the amount of sliding. I just got tired of replacing (and buying) them when they got beat up too bad to straighten out .

Send Brian O'Leary of Outboard Jets an email at *[email protected]* and ask him about the fins. He can give you more information about how they will work on a tunnel boat than I ever could. He usually sends a reply within a day or so and he's very good about helping people out with questions about their boats.


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## rotus623

Thanks I will surely do that. I also believe that my impeller is dull because that is one of the main reasons for cavitation on acceleration according
To outboard jets.


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## rotus623

So I had a little fun with my engine this weekend.

I pulled the spark plugs and put some fresh ones in, changed the oil, and adjusted the valve clearances. I sharpened the impeller a little bit more and took her for a spin.

I noticed that she got on plane a little easier without cavitation on take off. So that's a plus. I may want to experiment with a new impeller and possibly liner. I only have 2 washers to go on this one!!


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## Scottinva

If you fish those areas of the James you are very close to Jim Starkey at JRJ. He may have been the one that built the boat, but if not, he could certainly help you with your issues.

Scott


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## rotus623

Scottinva said:


> If you fish those areas of the James you are very close to Jim Starkey at JRJ. He may have been the one that built the boat, but if not, he could certainly help you with your issues.
> 
> Scott



Yea he built the boat and I don't live far from him at all.


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## rotus623

Ok fellas, 

So I brought the boat out to Jim at JRJ. He took a look at it and said everything looked good as far as motor height, etc. BUT he trimmed the engine up and looked at the impeller and told me that the wrong side of the blades had been filed. Apparently the person that owned the boat ahead of me had filed down the wrong side. So when I saw the dull edge, I continued to file it down to sharpen the leading edge. He told me that the bottom edge of the blades shouldn't be tampered with and what my boat was actually doing was pushing water down rather than up into the jet housing. Dang man, expensive boo-boo!! Here is the impeller:


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## rotus623

P.S. if anyone has an aluminum or ss impeller they want to sell let me know!!


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## LarryMc

Actually, OBJ says that the upper side should not be filed down, just to file the burrs off enough to smooth out the upper side. As best I can tell from your photos, your impeller looks just like the illustrations in their Sharpening Instructions. 

Check it out;
https://outboardjets.com/download/miscellaneous_instructions/RESHARPENING%20IMPELLER%20BLADE%20LEADING%20EDGES.pdf


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## rotus623

Yea man that's what I thought!! Well what is ol Jim talking about then? Man I sure would hat to buy an impeller and not have it fix my issue. You don't happen to have an old aluminum impeller
Laying around do ya?


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## rotus623

Oh and they talk about bending he blades upward on OBJ but that's some pretty thick metal. How in the world???


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## LarryMc

rotus623 said:


> Yea man that's what I thought!! Well what is ol Jim talking about then? Man I sure would hat to buy an impeller and not have it fix my issue. You don't happen to have an old aluminum impeller
> Laying around do ya?



Actually, I do. It's a 6 7/8" (part# 106.23) that I bought from OBJ several years ago. It's in good shape if you decide you want to buy another aluminum impeller. The leading edges have a few dings in them but otherwise it's not worn at all. Last time I had in my motor, all the shims were still on the bottom and there was .030" clearance. 

I didn't see anything about bending the blades up. Got a link?


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## rotus623

Oh sorry it says blend underside of the blade duh....
Yea man shoot me a pm with what you will take for the impeller. I'd like to at least try it and see if it helps with my cavititation. I think there has been too much taken off my impeller.


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## Lil' Blue Rude

You might be able to save your impeller, or at least make it little better. Attached a pic, trim it down like the red line shows and I think that should help it out. I've had impellers sharpened like that that cavitated on holeshot and I trimmed them like the pic and they hooked up better. 
I' not even getting started on the top vs bottom thing. :roll: :mrgreen:


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## rotus623

Lil' Blue Rude said:


> You might be able to save your impeller, or at least make it little better. Attached a pic, trim it down like the red line shows and I think that should help it out. I've had impellers sharpened like that that cavitated on holeshot and I trimmed them like the pic and they hooked up better.
> I' not even getting started on the top vs bottom thing. :roll: :mrgreen:



Lil blue thanks for your feedback. I have read some of your past posts regarding taking too much off the bottom of the blade, yielding EXACTLY what my symptoms are. I think you are on to something. I will try and salvage this impeller the way you describe, but am afraid that I will create an imbalance of the impeller. Guess you would feel it if it is off.

I'd like to see a pic of your impeller after you dress it.

Thankfully Larry has saved my @$$ and let me get a used impeller he doesn't need anymore. Don't have hundreds of dollars to be investing here!!


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## handyandy

Idk why obj suggest to sharpen the way they do. It works yes, but sharpening the way rude does gets much performance. I sharpen the top of mine works better for me.


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## rotus623

Ok fellas, thanks for all the support and ideas!! I think you guys and ol Starkey hit the nail on the head. I went out yesterday with a good friend of mine and the boat on plane with very little slippage/cavitation in a lite chop. On glass it didn't slip at all!! It's like a whole different boat.

Now the wind picked up and if the wind and current were going in a certain direction the cavitation would worsen, but I guess thats all in the game. I have the fins from outboard jets that I am going to put on for some less than stellar conditions.

If I had my passenger come up to where I set, the boat hopped up on plane in one boat length and ran shallower. It was awesome. I am going to try and figure out a way to get the passenger up closer to me when running. I am also considering moving the battery up front.


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## rotus623

I was afraid that bringing weight forward would take the rear of the boat up too much and make cavitation worse, when in reality, bringing the stern up basically elimintaes the cavitation even further. You guys think float pods are a good next step?


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## JL8Jeff

Which impeller did you use for this last run? I've never really noticed much cavitation except when trying to make a quick 180 turn at speed or going over multiple boat wakes, but I'm on a river where there really isn't too much activity. I never give it full throttle to get on plane, usually 1/2 or 2/3 at the most so I don't notice cavitation in that situation and that's with my chewed up impeller. When I had 3 people up front, I did notice the cavitation and had one guy move back to the middle with me, but I'm usually out by myself so that isn't a concern.


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## rotus623

I used a good used impeller that I got from Larry "The Man" MC!! It had never been filed at all and I just stuck it on there as is.

Clearly, the cavitation issue was caused due to way too much filing of the under side of the impeller. I kept all other factors exactly the same, down to the amount of gas I had and the person that I brought with me. I am very happy so for. Can't wait to add the fins on to see how they do in windy/choppy waters.


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## handyandy

I don't see why pods would hurt they would just give you more flotation in the back of the boat to help make it draft less.


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## rotus623

Ok fellas,

I am bringing this thread back to life here.

I am playing with ideas to get the boat to draft less while on plane. I also still have some undesireable cavitation in certain condition. It is not terrible, but I would like to make it better. I would also like to help with holeshot some. I really do appreciate having the 4 stroke engine though. It is so quiet and smooth. I can toss my anchor over and pop her in reverse and just wait til the anchor locks in. Then I leave it in reverse and throw out the back anchor. Snug up the lines and cut the motor off. Works like a charm!!

That being said, I did notice that the bottom of my boat, just before the tunnel, has about a 1/4" deep hook. The hook is 2' long and looks like I need to hammer it out from inside the boat. My guess is because of the weight setting on the roller trailer. In order to do that I need to pull the floor, and possible cut the rear box out (which I dont like anyways.)

Do you think the hook could be adding to the cavitation?

I am hoping to bring the passenger up front with me to help with weight distribution. When I am the only one on this boat it rides LIKE A DREAM!! Add another @$$, and not so much. My fear is that if I bring the tail end up more, I will cavitate more in the chop. Ulgghhhh.


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## jtf

I'm on the back end of this topic, it's interesting because I run a UHMW Hyde drift boat now, and three former UHMW bottom boats, one we retrofitted the bottom in the machine shop. 

All the boats are flat/rocker bottom without strakes. And that probably makes a big difference. I don't think the weight is as big a factor, the material we use can't be much more than 30lbs on a 14ft. The Koffler RMTB 14/54 would get up and go with 10hp and three adults. Doubt it ran 20mph, but it responded well, did slide pushed hard in a turn but that's how the hull is supposed to do on these and why we can run class III.

Jon boat hulls are different. If I try it on one, will put the UHMW between the strakes and expect to loose some handling. I think my UHMW bottom adds some lift while drifting.


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## Samsdad1

Hey rotus623, I guess you are the one on Cville Craigslist that was selling the 60/40... I live in western Goochland and just acquired a 1997 sea ark allwelded 17' with a 90/65 2 stroke... Would be glad to demo for you though my boat is lighter it would be a decent comparison. I had mine out for the first time since buying (waiting on the title) two weeks ago and it does 32 down river and 30 up... at Watkins landing...


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