# Impeller tolerance



## smackdaddy53 (Aug 27, 2014)

I finally got to run my jet and it ran fine on the hose but once I ran it in the water for a few minutes the impeller started contacting the liner. I had exactly .030" all around tolerances with my feeler gauge before I ran it. Did the tolerance change because of the load the water put in it pulling it down? Why is there no literature on this anywhere? Good thing I have a stainless impeller and an extra liner. 
Thanks


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## brianb2247 (Aug 27, 2014)

other than that how did it perform on the water , does it feel like a nemitz class destroyer


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## blazer02 (Aug 27, 2014)

Sounds to me like you had something loosen up and it dropped it down.have never heard or water pulling one down unless it was lose.i ment be rong but i believe a stainless can be ran at something like .015 even but not sure.


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## dhoganjr (Aug 27, 2014)

A stainless doesn't flex as much and can run a little closer tolerance. Did you have the nut tight and washer tabs bent around it. If there was anything between the washers sand , grit or anything else could have caused it. In the water as soon as you fire it up it will pull down if the nut not tight. The key could have got caught as you tightened it not allowing it to seat correctly.

Take the shoe off and check everything, make sure it is seated and everything is tight. If it is tight and everything is in place with the correct clearance, it should not hit.


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## dhoganjr (Aug 27, 2014)

There will also be a little back and forth play with the impeller. Grab it and turn it counter clockwise as far as it will go, as this is the direction the water will force it, before tightening it down.


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## smackdaddy53 (Aug 27, 2014)

I installed a new bearing kit with all seals recently as well. I was meticulous about assembling and cleaning everything and there was no grit between the shim washers or anything on the drive shaft. It ran fine on the hose but when I got it in the water and started getting on it something did not feel right so I shut it down. The bearing is installed correctly as well or it would have failed already. I ran it slow to get the feel of it for at least twenty minutes and slowly picked up thd pace. I am using the correct lubriplate grease and greased it when I got home and the grease came out clean so it isn't the bearing. I ran it on the hose when I got home with the foot off and it ran like a champ. 
Other than this small problem do you guys think a 60/45 Mercury Jet is not enough motor for my hull? I am going to re shim it and do a full day of running and adjusting until I get optimum performance then call it if I need to just get a bigger motor. 
I have researched outboard jets for three years and it seems like my motor should perform decent with my hull setup but real world performance of one rig could vary greatly from a hundred others. 
Thanks for the replies, I want to keep this thread going until You guys gelp me figure this out. I want to keep the draft as little as possible and get the performane I want if it is possible because this is a poling skiff that needs to float fairly skinny.


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## dhoganjr (Aug 28, 2014)

The 60/45 should push it just fine. Around here guys run them on 1856's and other hulls loaded down because of the 40 hp restrictions on the Current River. Size is not the problem, need to figure out what the issues are and go from there.

I'm not much help on the bearing side, never had to change one, but know that they have to be done correctly or they self destruct quickly. Since you are sure that it is not the bearings, get the reshimming done and go from there.


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## Brian J (Aug 28, 2014)

Try taking one shim out. Had the same problem back in May when I put a new liner in our jet. It would run on the hose, but wouldn't turn over in the water. Switched one shim washer and it was fine.


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## smackdaddy53 (Aug 28, 2014)

Thanks guys. Next week I will have a couple of full days I can take it to the lake and run it and tweak it until I get it set where it needs to be. I didn't expect to put it in the water and have it set up perfect. It ran a few laps but never really had enough room to get on plane where I was running. I will touch base again in a few days and get this thread going again. I appreciate the input and keep it coming if you have any thoughts or similar issues that may help me.


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## Jetboater-TB (Sep 1, 2014)

Maybe I missed it, but how do you know the impeller is contacting the sleeve while you're running the engine? What symptoms are you seeing? Are there marks from the impeller contacting the sleeve?


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## smackdaddy53 (Sep 2, 2014)

Jetboater-TB said:


> Maybe I missed it, but how do you know the impeller is contacting the sleeve while you're running the engine? What symptoms are you seeing? Are there marks from the impeller contacting the sleeve?


There are grooves in the liner and I can see the deepest ones are closer to the bottom. There was a small wad of aluminum shavings on the edge of the stainless impeller and this is what made the other grooves in the liner. I cleaned it up, removed one washer from the top and added to the bottom and the tolerance is better. I am going to run it tomorrow and see how I need to set my motor to get on plane. 
Do you guys really think I need to have power trim to adjust on the fly or is a static setting fine? I see a lot of outboard jets without trim.


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## dhoganjr (Sep 2, 2014)

It will run ok without when you get it set correctly. However, with power trim you would probably gain a couple mph.

The reason is without power trim you have to choose where it performs the best with no adjustments under way. Tucked under gives you the best hole shot without cavitation, best speed and top end comes with motor trimmed level. You have to choose somewhere in between. 

With power trim you get the best of both, tucked under on take-off and trim out as it comes on plane. Gives you less shoe in the water for less drag and more clearance, allowing you to run shallower without hitting bottom as much. The more speed you can get the more of the hull will be out of the water. 

So to answer your question, yes it will perform, you just won't be able to get top performance out of it. Personally I will never own another outboard without it.


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## JoshKeller (Sep 2, 2014)

how does tilt and trim fair to a direct rock hit? I know on my 50/35, the motor just kicks up. would hydraulic trim allow that without having to rebuild the seals?


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## dhoganjr (Sep 2, 2014)

Trim holds it in place, it will not kick up like it does without trim. But with power trim the shoe is about 1" lower to level with the bottom of the boat on plane trimmed out, so normally it takes less hits. 

Without trim it is usually 3 to 4 inches below the hull, so it is more prone to direct hits.

Most of the time on mine when I hear something start to hit the bottom of the boat I trim up more and throttle back a little if it starts to cavitate so it doesn't overrev, usually saves the shoe except for bent grates.


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## smackdaddy53 (Sep 2, 2014)

How much play should the shaft have left and right? I read with a stainless impeller you can go to within .015" but it feels like my shaft moves at least that much when I remove the foot and give it a little wiggle. Is this normal or did I somehow not install my bearing kit correctly? Looking at the mechanics of it there really should not be any play at all because the bearing is pressed on and the housing holds the bearing in place with four bolts. I am positive I installed the kit correctly and definitely have plenty of grease in the system because I shot some in twice already and it came out clean from the grease return hose. 
I ran it on the hose this afternoon after I re shimmed and the tolerance is definitely where it needs to be but still had a little contact with the liner. 
I hate to keep asking all these questions but I really thought this was going to be fairly cut and dried. Next step is to just put all shims on the nut side of the impeller and try it. I just bought this impeller and liner and I am not at all thrilled about ruining one liner already and scratching up the edges of my $380 stainless impeller. It just seems that if I remove all the shims from behind the impeller my leading edge impeller tolerance is going to be a hell of a lot more than .030".


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## dhoganjr (Sep 2, 2014)

With a new impeller and liner most of the shims should be on the nut side to start with, all but about 1 or 2 usually. As the impeller and liner wear you move 1 or 2 to the top or inside of the impeller to move it closer to the liner to keep the tolerance correct. If I'm reading correctly you are starting with most of them on the wrong side.


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## dhoganjr (Sep 2, 2014)

Here are some pic's to show the difference trim makes. This is trimmed down or tucked under. 
https://i105.photobucket.com/albums/m219/dhoganjr/Mobile%20Uploads/2014-09/20140902_193011_zpsicioivuz.jpg

Here is trimmed out level where it runs on plane and will run trimmed past level.
https://i105.photobucket.com/albums/m219/dhoganjr/Mobile%20Uploads/2014-09/20140902_193229_zpscrrptgui.jpg

This is the shoe with about 21 hours on it, notice how the leading edge and front half have very few nicks and most all the paint left. Properly set any hits should occur on the grates or the rear half of the shoe.
https://i105.photobucket.com/albums/m219/dhoganjr/Mobile%20Uploads/2014-09/20140902_193444_zps8veu361k.jpg


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## smackdaddy53 (Sep 2, 2014)

dhoganjr said:


> With a new impeller and liner most of the shims should be on the nut side to start with, all but about 1 or 2 usually. As the impeller and liner wear you move 1 or 2 to the top or inside of the impeller to move it closer to the liner to keep the tolerance correct. If I'm reading correctly you are starting with most of them on the wrong side.


No, I had three shim washers on top (bearing side) of impeller and the spares on the bottom (nut side) and it was contacting tge liner so I moved one from top so it gave the impeller more clearance. As the liner wears common sense tells me I will move more shim washers to the top of the impeller to maintain proper clearance.
I am just wondering why my shaft is moving so much and if it is normal. There is at least 1/16" play left to right but none up and down. This tells me there is no way I can get .030" tolerance with that much movement. 
I guess what I'm saying is I must be overthinking this and I should just not shim my impeller at all and go from there. Sound about right?


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## Jetboater-TB (Sep 2, 2014)

A little looseness if normal before its all bolted up. This note is from OBJ's web troubleshooting web page: https://outboardjets.com/troubleshooting/

Driveshaft wobble in bearing housing before assembly

Before the driveshaft assembly is mounted in the motor, the driveshaft will appear to wobble in the bearings. This is a normal condition. When mounted in the motor, the upper end of the driveshaft is supported in the crankshaft and the system becomes quite rigid under load. If you are concerned about the condition of the bearings, watch the texture of the grease coming out of the lube hose during lubrication. The 630-AA Lubriplate grease coming out will normally be light gray. If water is present, the seals need to be replaced. If the grease starts turning dark gray, the bearing should be inspected and replaced if necessary.


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## dhoganjr (Sep 2, 2014)

[url=https://www.tinboats.net/forum/viewtopic.php?p=365254#p365254 said:


> smackdaddy53 » 02 Sep 2014, 20:52[/url]"]
> 
> 
> dhoganjr said:
> ...



From your earlier post just wanted to make sure they were on the correct side. If it is rubbing any at all out of water it will flex a bit under load and rub more in the water. Try them all on the nut side and see where you are. Unless the bearings are not completely seated or you have a bent shaft everything should line up correctly. You said the bearings were installed correctly so I would rule that out. 

About the play in the shaft, I don't think mine has any play. Did you get a new Teflon or plastic sleeve with the impeller, goes between impeller and shaft and has a slot for the key to fit in. 

Hope I am helping you, I know it is frustrating when things aren't working correctly.


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## smackdaddy53 (Sep 3, 2014)

Jetboater-
I read all that, I researched just about every website, forum etc trying to learn about what I was getting into. I understand there is play before the shaft/bearing housing is bolted up. My issue is after being bolted up I still have a little play in the shaft. I have a new sleeve and key so it is not that. If this is one of those issues I just can't fix I may just sell the jet pump and go with a prop unit. 
Dhogan-
Yes it is frustrating but I will give it some time. Reading and real world experience are very different as many of us know! I am going to get after it more tomorrow and get it in the water to figure this out.


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## dhoganjr (Sep 3, 2014)

I would suggest giving Troutt & Sons a call, ask for Chris in the service dept. Tell him what is going on, he should be able to get you going. With that much play I think it is something more than I can help with at this point. https://www.trouttandsons.com


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## Jetboater-TB (Sep 3, 2014)

Does the motor push you along OK? If it runs OK, I wouldn't worry about it. A little contact is not a fatal flaw. I've heard some guys even install it so the impeller touches the liner, and let it wear in, especially with a stainless impeller.

Another thought is that the impeller nut could be loose, letting the impeller wobble around at start-up and shut-down. When its running, the up-thrust holds it in place.

That could explain your loose aluminum shavings. They could have happened on shut-down if the impeller was wobbling. Hard to imaging the shavings not getting blown out of the pump if they happened while it was running. Are you sure the play in the shaft that you're seeing isn't mostly play between the impeller and the shaft? You could try to get a thin feeler gage under the nut.


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## smackdaddy53 (Sep 3, 2014)

I ran it today a little and it was fine other than needing to be tucked under more. I have the motor set on the last hole tucked under as far as it goes and it definitely does not ride bow high like it did on the runs right before where I had the motor trimmed up two pegs higher. I bought some aluminum transom wedges to get the jet pointing a little more down and I will be installing them tomorrow. 
I still feel like the motor is not enough to really jump up like I keep hearing other guys talk about. It is hard to believe guys on here stating they run 50/35 jets on boats as big or bigger than mine with two or three guys and gear and they are getting 25-30mph. I am going to play with settings until I am either happy or I will end up selling this motor and getting a 90 merc jet or just say screw it and get a prop unit for it. I really expected this boat to be more lively.


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## Jetboater-TB (Sep 3, 2014)

I haven't seen a description of your boat and layout. Would like to see your boat specs and the performance you're seeing. Here is what mine looks like for comparison.

I ran a 40/30 Merc on my Roughneck 1655 tunnel hull for almost 20 years. Best it would do is about 24 MPH, but it would jump on plane right now. It was underpowered, but worked just fine. Just upgraded to a 60/45 Merc, and now it goes a little better than 29 MPH tops, downhill through shallow rapids. I have the front of the intake foot about even with the top of the tunnel, so the whole jet nozzle is out of the water, and the whole foot is above the bottom of the hull. I can't run the motor with someone standing on the front deck, because it will lift the whole intake foot out of the water. When I hit something, I hit it with the hull. (If you're not hitting stuff, you're reading the wrong forum.)

The 60/45 gets to top speed quicker now, and will cruise at 24 MPH easy at about 2/3 throttle. The new motor has a 3 blade Stainless impeller. I think any faster than 29 on my home waters, and you're risking going out of the boat if anything bad happens. Fast enough for me in my old age, especially with about no water under you.

My boat is light, with a 14 gallon gas tank, 1 battery, trolling motor, 15 pound anchor and 2-bank charger up front, and only 1 battery and the engine in the back. No livewells, big decks or other heavy things. Not even seats, except for a light plastic swivel seat for the driver. Console is on the right side about 6 feet from the bow. It floats and planes almost dead level.


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## smackdaddy53 (Sep 3, 2014)

Jetboater-TB said:


> I haven't seen a description of your boat and layout. Would like to see your boat specs and the performance you're seeing. Here is what mine looks like for comparison.
> 
> I ran a 40/30 Merc on my Roughneck 1655 tunnel hull for almost 20 years. Best it would do is about 24 MPH, but it would jump on plane right now. It was underpowered, but worked just fine. Just upgraded to a 60/45 Merc, and now it goes a little better than 29 MPH tops, downhill through shallow rapids. I have the front of the intake foot about even with the top of the tunnel, so the whole jet nozzle is out of the water, and the whole foot is above the bottom of the hull. I can't run the motor with someone standing on the front deck, because it will lift the whole intake foot out of the water. When I hit something, I hit it with the hull. (If you're not hitting stuff, you're reading the wrong forum.)
> 
> ...


My boat is definitely not bare bones. Check out my build on the jon boats and v bottoms under "smackdaddy's pole dancer tunnel jet".
1652 with 6" step pods, front and rear deck, trolling motor, 4 optimas under console, 25 gallon gas tank under bow deck. Right now I am running it with 5 gallons of gas in the tank. I may fill it up and see what happens but I am not too optimistic. I may be going with a 90 or even a 115 by the looks of it. My motor is strong. Less than 80 hours, fresh carbs, about to throw in some carson racing reeds and maybe an exhaust tuner to gain some HP. I may even do some real motor work and see what happens. I would like to keep my draft where it is, close to 6" but don't see that happening with a 90 or 115. Brand new stainless 3 blade impeller with no sharpened edges or buffed jet castings but I will do that at some point. I have not weighed my boat but I guesstimate 1000# with everything plus me which may be conservative. 
Here is my framing- 2x2x1/8" tubing with 1/8" decking.


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## dhoganjr (Sep 3, 2014)

I can tell you a 115/80 Fourstroke pushed my 1860 to 36 mph gps flat out, 1-2 mph faster down river. It ran good with just me but add more gear and people and it was way underpowered and took a runway to climb on plane. The boat has extended front deck and rear deck, 24 volt trolling motor, 2 batteries under front deck, livewell, rod box, 2-12 gallon fuel tanks and starting battery in rear. The 250/175 pushes same load plus 3 gallon oil tank in rear to 49 mph.

Semojet runs a 1856 with a 60/40 Fourstroke and gets about 30-31 if I remember right.

I think Lil Blue Rude is running mid to upper 40's with a 60/40, extensively modified of course.

I think you should be seeing at or near 30 with your setup and it should plane pretty good with a 60/40, why it is not I don't know.

I don't know what your boat is rated for but most 90 and 115's are in the same weight class if that is the direction you go and with pods should only draft about an inch more.


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## smackdaddy53 (Sep 4, 2014)

Since I have a nice clean motor maybe I should just modify the hell out of it and see what happens. For now I am going to keep moving weight around and setting the motor. 
I don't care much about speed as just getting out of the hole and on plane as fast as possible.


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## dhoganjr (Sep 4, 2014)

Just wanted to give you a ballpark on where it should be with verified numbers.


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## smackdaddy53 (Sep 4, 2014)

dhoganjr said:


> Just wanted to give you a ballpark on where it should be with verified numbers.


I appreciate it! I am about to start on it.


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## smackdaddy53 (Sep 4, 2014)

I got my transom wedges and splash plate fabbed and installed. I think this is the ticket! I am going to run it tomorrow (weather permitting) and see how it performs. I believe I am going to put about 10 gallons of gas in the tank to help get some weight forward.


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## LarryMc (Sep 6, 2014)

[url=https://forum.tinboats.net/viewtopic.php?p=365243#p365243 said:


> smackdaddy53 » 02 Sep 2014, 20:38[/url]"]How much play should the shaft have left and right? I read with a stainless impeller you can go to within .015" but it feels like my shaft moves at least that much when I remove the foot and give it a little wiggle. Is this normal or did I somehow not install my bearing kit correctly? Looking at the mechanics of it there really should not be any play at all because the bearing is pressed on and the housing holds the bearing in place with four bolts. I am positive I installed the kit correctly and definitely have plenty of grease in the system because I shot some in twice already and it came out clean from the grease return hose.
> I ran it on the hose this afternoon after I re shimmed and the tolerance is definitely where it needs to be but still had a little contact with the liner.
> I hate to keep asking all these questions but I really thought this was going to be fairly cut and dried. Next step is to just put all shims on the nut side of the impeller and try it. I just bought this impeller and liner and I am not at all thrilled about ruining one liner already and scratching up the edges of my $380 stainless impeller. It just seems that if I remove all the shims from behind the impeller my leading edge impeller tolerance is going to be a hell of a lot more than .030".



I don't think you should have any side to side play after bolting the shaft back in. If it were me, I would call Outboard Jets and ask them about it. One thing to check, is the bearing carrier still in the same place on the shaft where it was after you installed the bearing kit and pressed the carrier back on? About 4 years ago, the shaft on my motor slipped down through the bearing carrier about 3/16" and ruined both my liner and the impeller. Had to buy a new shaft, liner and impeller. It's entirely possible that your shaft slipped down a little after running for a while and caused the impeller to start hitting the liner.

FYI, about a month ago I put a new liner and new stainless impeller in my 2005 Merc 60/40 along with a shaft rebuilt by Outboard Jets. With all the shims on the nut side, the clearance was .020".


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## smackdaddy53 (Sep 6, 2014)

LarryMc said:


> [url=https://forum.tinboats.net/viewtopic.php?p=365243#p365243 said:
> 
> 
> > smackdaddy53 » 02 Sep 2014, 20:38[/url]"]How much play should the shaft have left and right? I read with a stainless impeller you can go to within .015" but it feels like my shaft moves at least that much when I remove the foot and give it a little wiggle. Is this normal or did I somehow not install my bearing kit correctly? Looking at the mechanics of it there really should not be any play at all because the bearing is pressed on and the housing holds the bearing in place with four bolts. I am positive I installed the kit correctly and definitely have plenty of grease in the system because I shot some in twice already and it came out clean from the grease return hose.
> ...


The tolerance is not an issue any more, now I am wondering what the issue is with my setup and why I can't get on plane. 
This morning I replaced the factory stainless reeds with Carson racing reeds and inatalled transom wedges to tuck the motor under more so I could maybe get the nose down. WRONG AGAIN!
I ran by myself with 15 gallons of gas in the bow tank and it still dogs. I am not sure what the deal is. I am going to keep picking yalls brain and Monday I am taking this rig to Sonny's Marine and see what he thinks the deal is. He has been running and rigging jets on rigs like ours for 20 years. 
Here are a few pics of the rear end. Anything look out of place or just wrong? 
I am having a hard time convincing myself the 60 is underpowered for this boat but who knows. I know one thing, 17.8 mph today was the fastest I could get it but it never fully got on plane. Do I need trim tabs and/or power tilt to help get it up? The motor is running great but something is just not right.


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## dhoganjr (Sep 6, 2014)

One question come to mind, do you have a tachometer on there to verify that you are turning max rated rpm's .


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## LarryMc (Sep 6, 2014)

[url=https://forum.tinboats.net/viewtopic.php?p=365635#p365635 said:


> dhoganjr » 06 Sep 2014, 20:34[/url]"]One question come to mind, do you have a tachometer on there to verify that you are turning max rated rpm's .



I was thinking the same thing. At WOT for that motor you should be running between 5000 & 5500 RPM. My motor runs 5250 at WOT.

What size is your tunnel? It looks pretty big to me in the photo.


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## smackdaddy53 (Sep 6, 2014)

Still trying to figure out what setting to set the dial on the back of my tach. I do know the motor is definitely not bogging down. If it were cavitating I would probably hear it right?


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## dhoganjr (Sep 6, 2014)

The motor setting and height all looks good. I'm betting it's not turning max rpm's. It will run fine and not bog down, but if you are not getting full throttle you will have a hard time planing and getting speed. You would know if it was not running correctly, but not if it's not turning full rpm's without the tach telling you so. I say get the tach working asap, I am guessing it could be in the linkages. 

With motor off put it in full throttle and make sure the butterflies are fully open. I think we may have been working on the wrong end.


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## smackdaddy53 (Sep 6, 2014)

dhoganjr said:


> The motor setting and height all looks good. I'm betting it's not turning max rpm's. It will run fine and not bog down, but if you are not getting full throttle you will have a hard time planing and getting speed. You would know if it was not running correctly, but not if it's not turning full rpm's without the tach telling you so. I say get the tach working asap, I am guessing it could be in the linkages.
> 
> With motor off put it in full throttle and make sure the butterflies are fully open. I think we may have been working on the wrong end.


You guys have to excuse my lack of knowlege as far as motors and jets because this is my first "real" boat. I can build and learn just about anything but I have to have hands on experience rather than just research. 
dhogan, That makes sense because I have only adjusted the idle by ear and have not even messed with the throttle settings. That may also explain why I have to push the lever so far forward to get much response. 
I looked up my tach and it shows I need to set it on 6P for my motor. Here is a pic of the back of my tach.


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## dhoganjr (Sep 6, 2014)

Setting up the tach, I don't know much about. But the throttle linkage where the cable attaches to the motor controls all 3 butterflies and can be adjusted on the linkage. Check that when you open it to full throttle all 3 fully open. I hope that is the problem because that is a simple fix. 

It just happened to come to mind when you said it only got 17.8 and never got on plane, that would be around the 3500 rpm range just guessing. I know a 60/40-45, whichever it is, should plane that boat pretty quick and should get near 30 mph.


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## smackdaddy53 (Sep 6, 2014)

I sure hope you are right bro! I was about ready to get a 90


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## dhoganjr (Sep 6, 2014)

[url=https://forum.tinboats.net/viewtopic.php?p=365654#p365654 said:


> smackdaddy53 » 06 Sep 2014, 22:11[/url]"]I sure hope you are right bro! I was about ready to get a 90



I hope so too, you would love a 90 on there, but I know you are trying to keep the weight down. If you don't figure it out, definitely get it checked out by your marine shop. I'm almost sure it's going to be something with the adjustments.

I know the pump is pretty straight forward, just couldn't get it all to add up. Very few adjustments and it either works or doesn't. When you said it was running good I never thought about that end of it. #-o


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## smackdaddy53 (Sep 6, 2014)

Yeah, I want to draft as little as possible. I should have built it a little more scantily but I like sturdy.
We will see tomorrow! Thanks


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## dhoganjr (Sep 6, 2014)

Nothing wrong with sturdy, I get ribbed all the time for having a river barge.


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## Tbradley (Sep 7, 2014)

What about the setback of the jack plate? Should he have a splash plate to help direct the water to the intake? Maybe it's going over the foot?


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## JL8Jeff (Sep 7, 2014)

I wonder if it's your linkage or cable adjustments. I have a 1994 Mercury 60/45 jet on my Lowe 1652 tunnel jet and it flies at WOT. Maybe your gate isn't adjusted properly.


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## smackdaddy53 (Sep 7, 2014)

No way water is going over my foot, when the motor is straight the front edge of my foot is about 1" from my tunnel and when it is turned either way the corner of the foot actually goes over the edge of my tunnel a little. 
Jeff, how much does your boat weigh compared to mine? Mine is pretty stout. 
I am taking it to the mechanic tomorrow to synch timing and carbs and get everything set right as far as WOT and getting max rpms. We will see from there. I am about at wits end with it and thinking about just ordering a brand new Yamaha F90 Jet


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## smackdaddy53 (Sep 7, 2014)

LarryMc said:


> [url=https://forum.tinboats.net/viewtopic.php?p=365635#p365635 said:
> 
> 
> > dhoganjr » 06 Sep 2014, 20:34[/url]"]One question come to mind, do you have a tachometer on there to verify that you are turning max rated rpm's .
> ...


My tunnel is EXACTLY the same dimensions as a local guy has Alweld build jet tunnels for his shop where he has been rigging, running and selling outboard jet rigs for over 20 years. I actually went to his shop and measured his tunnel and fabbed mine exactly like it. He runs 4 stroke 60/40's on his 1552's but they are flat bottoms bare bones and he gets well over 30mph out of his rigs. 
19" wide on bottom, 14" wide on top, 28" long, 2 3/4" deep, flat for the last 12". The only notable difference is it looks like his jet foot actually tucks under the leading wdge of his tunnel if you look at the picture. I am going to drag my boat to his shop tomorrow and see what he thinks the flaw is. I just set my height like everyone recommended on here, my tunnel hits right at the front grate pin hole. Is that possibly too high for mine? I know every boat is different and my design is not textbook but in theory it should work, I guess I have to just find out how! 
Here are two pictures of mine and his. 
Mine-


His-


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## JoshKeller (Sep 7, 2014)

im willing to bet you have a cylinder that isnt firing or getting fuel..


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## smackdaddy53 (Sep 7, 2014)

One more good pic of mine


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## smackdaddy53 (Sep 7, 2014)

JoshKeller said:


> im willing to bet you have a cylinder that isnt firing or getting fuel..


I had the compression checked and it was 118, 118, 117.
New plugs, motor sounds good from what I can tell.


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## JoshKeller (Sep 7, 2014)

verify you're getting spark/fuel on all 3 cylinders? keep in mind with a jet, theres no real resistance like a prop and it can sound like its reaching plenty of rpm with a cylinder down.


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## smackdaddy53 (Sep 7, 2014)

I definitely can't rule it out at this point. I am sure the mechanic can isolate the problem tomorrow. 
I pulled the plugs today and they were all dry and looked the same but who knows. I had to replace the oil warning sensor module so who's to say the CDI is not shot? At this point $250 is a drop in the hat, if it may fix it I will try it!


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## dhoganjr (Sep 8, 2014)

Since you mentioned replacing the oil warning sensor, I don't know if this one has the technology or not, but if they set a fault code it limits rpm's to around 2000 until reset.


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## dhoganjr (Sep 8, 2014)

Those intake fins should feed the pump with little if any cavitation. If it was you would know it, the rpm's would rise sharply with injected air until the pump loaded again causing it to surge. Exhaust sound would drastically change also.


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## JL8Jeff (Sep 8, 2014)

I think my hull is listed as 425 lbs but I have the center console and some extra weight up front. But it's pretty light compared to some of these well equipped boats. It reall sounds like you are not getting the top speed out of your motor.


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## smackdaddy53 (Sep 8, 2014)

I don't think this motor has a computer, it is a 1997 Merc 60. 

The cylinder misfiring has me thinking about what I have been seeing. 
The air intake had some 2 stroke residue inside after the first time I ran it and I cleaned it out with brake cleaner and after the second run it did the same thing.
When the motor is idling I can see it jump every now and then hard enough for it to move the steering wheel each time. This may also explain the wobble causing the impeller to contact the liner. 
The motor also sounds like a bearing may be going out now, probably from running it with a misfiring cylinder. 
When I got the motor the shop said the compression was 118, 118, 117 and it was written by each spark plug too. The bearing was totally gone and the liner and impeller were chewed up from the bearing allowing the shaft to drop. I wonder if all of this is tied together? 
Im taking it to the mechanic her in about an hour and we shall see what he finds. It is all coming together now and sounding a lot like I'm going to get this one running, sell it and buy something else, maybe a Yamaha F70 Jet.


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## smackdaddy53 (Sep 8, 2014)

No available mechanics today, dragging it 80 miles to a jet guy that knows his stuff at 8 in the morning. Hopefully all goes well.


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## JL8Jeff (Sep 8, 2014)

I tried to GPS mine tonight but it was windy goining upstream and the batteries were dying in the portable GPS so I got around 26 mph going upsteam into the wind before I lost the reading. It was cruising along on plane at 18 mph at 2/3 to 3/4 throttle easily. I don't normally run full throttle and it was starting to porpoise before I was getting the full reading anyway so I had to back out of it. My motor was beat up during Sandy and I'm surprised how well it still runs. I hope you have a simple issue like some sensor keeping you from getting WOT properly.


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## LarryMc (Sep 9, 2014)

After you posted the measurements, I can see that your tunnel isn't too big. In the photo, it just looked bigger than most jet tunnels. As for your height adjustment, all jets won't work with the height set even with the front pins. Mine is set even with the leading edge. Any higher and mine will cavitate. I don't think that cavitation is your problem though. If your pump was cavitating, it would over rev and you would hear the difference in the sound your motor makes. I'm in agreement with the guys that think your problem is that your motor isn't reaching full RPM.


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## smackdaddy53 (Sep 9, 2014)

So far we found pinholes and a crack on plug boots. When we went to grab the plug wire with the plug pliers with it running they were arcing to the pliers robbing spark. About to put some new boots on and see what happens.


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## smackdaddy53 (Sep 9, 2014)

Crankshaft bearings are about to go, they are rattling and causing the motor to run a little hotter than normal- 150-160 degrees. Still can't get max rpm's and he convinced me the motor would definitely be underpowered on my boat even if it ran right. I am selling this motor and either buying a used 90 or 115 jet or just biting the bullet and getting a brand new 115 4 stroke Jet. Damn things are 400# but I think my draft should not change much more than an inch or so. I am also considering either lithium batteries or just taking out one optima and running off one cranking/house battery to lighten the load.


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## dhoganjr (Sep 9, 2014)

I was hoping you would get better news and it would be something simple. But at least now you know what the problem is.

Since you are going to replace it, unless you can find one in excellent condition and know the history, I would go with a new one if you can afford it. Jets are usually run hard often hitting bottom and clogging up cooling passages and are usually run in the higher rpm range through most of their life. Most of the used ones were put on underpowered boats and upgraded to a bigger size later shortening their usable life as you have found out. If a used one is very new and well taken care of they usually want a pemium price which is not far from new.

Don't know which way your going, but a Yamaha 115 Fourstroke weighs 402 according to their website. The new Mercury 115 Fourstroke weighs according to the site 317, but it has moved around I think it weighs more, the prop version weighs 359 so I would guess it weighs around 340.
I have heard good reviews with this new design. With either option you get a 3 yr warranty for peace of mind and with a promotion you can usually get a 5 yr and can extend it to 7 yrs.

A 115 Fourstroke should jump that boat on plane in about a boat length and get between 35-38 mph. You will be able to cruise about 2/3 throttle easily and it will sip fuel and be quiet running.

My choice would be the new route and you can get financing on them if you need to. I bought my first one used and the other 2 new. Buying new I know it was broke in correctly and well taken care of. If you decide to get a new one follow the break-in schedule by the book, explains it in the manual.

Just my .02 worth, give you something to think about. I ran my Mercury 115 Fourstroke for 11 years, so if you have any more questions ask away.
Keep us updated on whatever you decide.


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## smackdaddy53 (Sep 9, 2014)

I appreciate you guys input for sure! 
The mechanic offered $1200 for my motor as-is but I think I will ask more for it because I have over $800 in brand new parts in it plus a new stainless impeller and liner I never installed. The pump with new bearings and impeller is alone worth at least $1800. That is a nice chunk of change to help the "ouch" of purchasing a new motor. 
I would love to find a new Yamaha 115 or 90 2 stroke but that is nearly impossible. I want the warranty. 
I will definitely check out the 115 4 stroke Mercury. Just the peace of mind I would have with a new motor would be well worth the price. The weight is not ideal jumping from drafting 6" with my 250# motor to at least 350# but I suppose once I'm on plane it won't matter much. I just want to draft as little as possible and jump on plane fairly quickly (in an ideal world there would still be light and torquey 2 strokes available).


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## dhoganjr (Sep 9, 2014)

With your pods I don't think your going to lose very much draft, except when standing on your platform of course. You may be able to offset this by moving anything forward that is possible. I would say 8" at most on draft and with a Fourstroke unless you are running long distances, you can go light on fuel for short trips.


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## smackdaddy53 (Sep 9, 2014)

With just me on the rear seat and 5 gallons of gas the stern squats a little over the 6" first step of the pods. If I put more fuel in the bow tank the draft equals out more and actually makes the stern raise up a little. With 15 gallons of gas I draft about 6", maybe 7 at most. We will see because either way I have to have more power!


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