# Need some help- Motor bogging at full throttle



## thill (Feb 28, 2014)

I'm putting together a deep-V aluminum boat, a 1957 Crestliner Viking 710. 

This is a nice, heavy, well-designed hull, factory equipped with either a 40 HP or a 60 HP Evinrude. Prev. owner gutted the boat and used it as a jon, with a 9.9 tiller. I've added a front deck, trolling motor, new transom, dual batteries, etc. Probably similar in weight as the original design.

To this, I have mounted a 1994 Evinrude 25 HP tiller motor on it, with whatever prop it came with. 

I cleaned the carbs, and the motor starts and idles great and jumps up on plane fine, and loaded normally, it reaches 23 MPH GPS, which I'm happy with. 

My PROBLEM is that the boat reaches max speed/RPM's at around 3/4 throttle. Any more throttle, and it gains no more RPM, and after a certain point, (when I give it full throttle) it actually bogs down and loses some RPM. No tach, so I don't know what the actual RPM is, but it sounds a little low.

*My guess is that my prop pitch is too high for this load. Does this sound correct?*

I just want a few other opinions before investing in a lower pitch prop. 

Thanks guys.

-TH


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## keelme (Feb 28, 2014)

could be air leak around fuel line fittings or fuel pump maybe not pumping enough fuel at top end


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## Pappy (Feb 28, 2014)

You could be correct on the prop pitch. However, it really should at least hold RPM and not drop or bog.
You can effectively eliminate the fuel pump by simply squeezing the primer bulb at the RPM where the problem occurs. Doubt this is the issue.
Although most carburetors have a roll pin driven through the throttle shaft and a cast-in stop on the carburetor main body do a check (engine shut off and in gear) to make sure this pin is near vertical when you advance the throttle to WOT. If for some reason it is able to go past vertical this may produce the symptoms mentioned. Doubt you will find this. 
What I can tell you is that, in the past few years, I am finding more and more engines with high speed jets that are eroded internally. These jets will typically be from .003 to .006 larger than the jet size stamped into them. When this happens the symptoms are exactly as you describe. The engine becomes over rich and will slow down at WOT throttle settings. 
Since you already know your way around the carburetor my advice to you would be to purchase a new high speed jet and install. BTW - if you did not do it initially purchase an OEM carb kit as well. It will have the float with it as well as a new packing for the low speed needle and alcohol resistant gaskets. 
You did put the high speed nozzle gasket back in place prior to re installing the fuel bowl I hope? Usually if not the symptoms are much worse than you describe.


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## thill (Feb 28, 2014)

Ahhh... Some interesting and thought-provoking replies!

I replaced all the fuel lines when I did the carbs, and did all the connections myself. Very confident that they are tight. But I did not replace the carb to block gaskets, so it's possible some air may be getting in... Will have to look at the plug condition to see if it looks like they are running lean. Good call!


ALSO, I just replaced the spark plugs yesterday, properly gapped. Champions, as per the manual.


When I cleaned the carbs, there was obvious Ethanol phase separation in the bottom of the bowls. You could see the line where water sat. This absolutely WILL cause corrosion/erosion of the main jet down there! Jets are $8 each. I'll order a pair ASAP. Good call!

As far as the bogging, let me clarify a bit. She hits max RPM at about 3/4 throttle, and it stays there the rest of the way, until you pin it open, and there she actually slows down a little. Not a ton, but enough to lose maybe 2 MPH if you hold it there. So your description of the eroded jets fits!

So what I've been doing is run her until I reach 23 MPH, and then hold it there or a little less. My reasoning is that if pouring extra gas in the cylinder isn't increasing output, it's just leaving unburned fuel and creating heat. I don't want to burn up my motor!

Getting ready to go out and check my prop pitch. Very curious as to what it is...

Thanks.

-TH


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## thill (Feb 28, 2014)

OK, went out and checked the prop. It's a 10" x 13 pitch aluminum. Not in bad shape at all, but it is missing the condensing ring around the back end of the hub. Would this cause any problems???

From what I remember, I think other guys are running an 11 pitch with their 25 HP's on heavier boats.

Any thoughts?

-TH


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## Boat2fast (Feb 28, 2014)

You can't be that far off on the prop pitch. It still needs to be set-up with a tach. I can't even sleep at night if I put on a new prop and don't check it _with a tach_.

Pappys comment made me think of something. I see this occasionally. Sometimes an inexperienced mechanic will get in there and make adjustments to the throttle linkage. On your engine it's real easy to mis-adjust the linkage that operates the carb. It can push the carb right past 'wide open' until it's actually closing it down again. This adjustment needs to be checked whenever the throttle linkage is disturbed at all. You can tell by the little roll-pin in the throttle shaft, see if it's vertical at WOT

This adjustment is called "linkage adjustment and synchronization" or 'link 'n sync'. The procedure needs to be followed step by step as laid out in the factory service manual. I have the manual for your engine. If I can figure out how to scan the procedure I will forward it to you.


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## Pappy (Feb 28, 2014)

[url=https://www.tinboats.net/forum/viewtopic.php?p=343148#p343148 said:


> thill » Yesterday, 10:57[/url]"]
> I replaced all the fuel lines when I did the carbs, and did all the connections myself. Very confident that they are tight. But I did not replace the carb to block gaskets, so it's possible some air may be getting in... Will have to look at the plug condition to see if it looks like they are running lean. Good call!
> -TH



You can pretty much forget that as a cause. The symptoms would be very evident at an idle if that gasket was leaking air. 
Also, there should only be a single high speed jet to purchase.


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## thill (Mar 1, 2014)

I read your post and went out to check the carb movement, and it's right on. Completely closed to full open, right on the button, everything aligned properly.

But then I thought about it... The timing. What I'm probably hearing is the timing not advancing enough or advancing too much. That would certainly explain the lagging engine speed when I go past a certain point.

It's only 12 degrees outside right now, but when it warms this afternoon, I'm putting a timing light on that baby! Maybe it's that simple!

You guys are great! Will report back later.

Thanks.

-TH


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## Pappy (Mar 1, 2014)

Wont be timing either. 
The timing is fixed as part of the mag plate. Wherever the mag plate stops so does the timing. Check it if you want....will only make you more familiar with the engine so never a bad thing.
Also....on a 2-stroke.....advance the timing a few degrees too much and you can take the piston out in pieces usually!


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## Gotem (Mar 1, 2014)

Could it be a powerpack?


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## thill (Mar 1, 2014)

OK, next update...

Boat2Fast sent some helpful information, (thanks!) and I went out and double checked the sync and link. Again, it was dead on the money. 

But while under there, I was reminded that everything under the hood is really gummy and sticky. Someone sprayed storage grease on everything, and it's dried out and gotten stiff. Even my recoil start cord retracts VERY slowly, taking maybe 5 seconds to recoil between pulls.

So I took a pump bottle of WD40, and sprayed everything down, and exercised it back and forth. Within a few seconds, everything loosened up and is moving smoothly, as it should. I'm wondering if that wasn't half of my problem? Maybe the sticky stuff wasn't allowing my timing plate to advance fully?

Something then occurred to me... I THINK when I ran the boat in warm weather (only once) it reached full RPM's, and this problem started when it got cold. No adjustments at all since then. So the sticky stuff under there MAY have something to do with this?

But either way, as you say, I need to learn how to check/adjust timing. A few questions:

1. How/where do I connect a tachometer to test with?
2. Can I use a regular tach with alligator clips, or does it have to be a diagnostic unit?
3. Does it need to have a stator for the tach to work properly? I have a stator, terminal strip and rectifier that I plan to put on the motor eventually. Should I put that on first?
4. Would it be OK to test WOT while tied off on a dock? I don't have a test wheel to use in my tank.

Thanks, guys!

-Tony


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## thill (Mar 1, 2014)

[url=https://www.tinboats.net/forum/viewtopic.php?p=343256#p343256 said:


> Gotem » Today, 13:29[/url]"]Could it be a powerpack?



Sorry, didn't see your post!

I suppose it could be the powerpack getting "weak" but it runs great all day, with the exception of when the throttle is cranked all the way, so I'm not sure about that. You would think it would get weaker as time went on, from it getting hot.

I'm also thinking that I should pull the bowl and make sure there is nothing gumming up the main jet or tube. I cleaned the carbs carefully, but maybe a piece of hose got in there before I changed them out? Those hoses were pretty bad, and were shedding chunks on the inside.

This is an interesting search! Hopefully, I will learn something before it's over. I'll be sure to post all progress, so as to possibly help someone else while I'm learning.

Thanks!

-TH


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## Pappy (Mar 1, 2014)

You seem to be forgetting about replacing the main jet.
Your mag plate is a straight mechanical connection. Gummy or not it will advance to a pre set limit. Also the lubrication for that plate is in a place where a sprayed on corrosion preventative cannot reach.


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## thill (Mar 1, 2014)

Pappy,
No, I have absolutely NOT forgotten the jet! That is a simple, easy, inexpensive fix, and it fits the symptoms. I just want to eliminate anything else that might be contributing in the mean time. I would have ordered it already, but the jet is $8, and shipping is $12! Should cost maybe $1-$2 for a padded envelope. Plan to call the local OMC shop to see if they have that jet in stock.

But that spray grease stuff had EVERYTHING sticky, including the timing plate, linkage, and even the pull start recoil, which is way up under the cover, and really hard to even see. Who ever applied that spray, really got it up in there!

In the meantime, I need to learn how to time a motor properly, and as they say, no time like the present.

Hopefully on Monday, the marina will have a main jet for me, and I can swap them out.

Thanks again!

-TH


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## Charger25 (Mar 2, 2014)

*I'm also thinking that I should pull the bowl and make sure there is nothing gumming up the main jet or tube. I cleaned the carbs carefully, but maybe a piece of hose got in there before I changed them out? Those hoses were pretty bad, and were shedding chunks on the inside*.

I'm a big fan of keeping it simple. If all the mechanical parts are moving freely ,link n sync are good , electrical parts are good (no frayed wires) I would look at some kind of fuel restriction somewhere, from the tank through primer bulb through hoses and out of the back of the carb. Even with too high a pitch prop you would not lose RPM's you just won't get to top end. I would rule out the prop though simply because it was stated that it jumps up on plane.


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## Pappy (Mar 2, 2014)

Chances are they will not have it in stock but the nice part is that they can include it with their normal parts order and no shipping costs to you!
Good way to check and see if the engine is running lean, since it was suggested, is to engage the primer at the RPM where the issue occurs or if not primer equipped a spray bottle with a mixture of 50:1 can be used and sprayed down the carb throat. If the engine picks up and runs you have a restriction. 
Which brings me to another question. Does your engine have a choke or primer? If it has a primer make sure the primer is locked in the fully closed position or it will flow fuel through it and richen the mixture. Push it in hard and see if it locks closed. A second way to tell if the primer is leaking internally is to simply pull the hose off the barb above the carb or pinch off the supply line to the primer with a pair of pliers, again at the RPM where the issue is occurring. If it picks up now then the primer was leaking fuel through it.


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## thill (Mar 2, 2014)

Pappy,
Yes, this engine HAS had primer issues. 

My engine has the choke/pump primer. The kind where you pull it out and it sprays gas into the carb like a pump bottle. Recently, that got clogged and locked up from the rubber bits from the old hose. 

When I forced it, it blew the primer hose off, spraying fuel everywhere. When I pulled the hose, I found that little orifice clogged with rubber bits. I cleaned it out several times, until everything worked well.

But YESTERDAY I noticed, that the primer hose was dripping/spraying fuel again. Your possible theory would explain a lot!

On my next trip out, I will bring a pair of hemostats and test it. Thank you again!

-TH


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## Boat2fast (Mar 2, 2014)

If there are rubber hose chunks all throughout the fuel system, then that needs to be addressed all at once. Everything from the connector all the way to the main jet. Any piece of material left in the system will move downstream to the largest hole it can't fit through. A little piece of that in your float needle will give you fits.


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## thill (Mar 3, 2014)

Yes, that stuff has been a pain! Like black flour, gumming stuff up. I've cleared it out 2-3 times already, and it finally seemed to be gone, until I found that bit the other day. 

It is some frustrating stuff! Not sure where it was hiding, but hopefully, another cleaning will be the last of it.

We are up to about 8" of snow now... I had planned to pull the carb today, but I don't want to uncover the boat in all this stuff. I guess it's time to work on the wife's honey-do list... <sigh>

-TH


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## Pappy (Mar 4, 2014)

[url=https://www.tinboats.net/forum/viewtopic.php?p=343454#p343454 said:


> thill » 02 Mar 2014, 21:37[/url]"]Pappy,
> When I forced it, it blew the primer hose off, spraying fuel everywhere. When I pulled the hose, I found that little orifice clogged with rubber bits. I cleaned it out several times, until everything worked well.
> -TH



Sounds like you are getting a good handle on this stuff!


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## thill (Mar 4, 2014)

I don't know if I would call it a good handle, yet... More like barely hanging on!

I'm still learning the basics. And that's why you fellows, who are kind enough to share their experience, are SO appreciated! Sorry if I keep saying thank you too much, but THANK YOU! 


Side question... What kind of boat is that under your scree name?

-TH


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## muddywaders (Mar 4, 2014)

Hey guys the motor symptoms described have me intrigued.I agree with pappy "bogging" is usually a sign of a too rich condition however at 3/4 thottle the motor should be running on the main jet so perhaps something other than a bad main jet is causing the problem.Not too familliar with O.M.C. stuff but I do recall some motors being equipped with a cold enrichment circuit instead of a choke.Could it be possible that at higher rpm too much fuel is drawn through this cold circuit which I believe has a valve of some kind on the primer?let us know what the problem was after you fix it.Cheers M.W.


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## thill (Mar 4, 2014)

...and that makes two, pointing toward the primer system.

Thanks for the insight, Muddywaders. At the top of page 2, Pappy made the same call. That really verifies the thought.

And at this point, I have to make a confession... This is the first motor I've ever had with this kind of primer system. With all the pulling to get her started, due to the rubber stuff in the system, I am NOT absolutely sure if I pushed the primer in all the way, after getting her started. I THINK I did, but I'm not 100% sure.

It pains me to say, but this MIGHT be user error. Half of me hopes so, but my pride hopes not! This makes me feel like a real idiot!

As soon as the snow melts and we get dug out, I'm running to the lake to test out, and will report back.

However it it goes, I owe you all a big thanks! 

-TH


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## Pappy (Mar 5, 2014)

Well, I had a little time today. 
Repaired a 1988 Johnson 30hp. This engine is close enough to your 25hp to do a comparison with. 
Once running on the hose I shut it off and backed it in a little way into the water and while on the trailer I throttled it up. Ran nice and steady which it should. 
Okay....satisfied I can now give it back to the customer I went ahead and pulled the primer out and left It out. Ran the engine to WOT again and, once steady, I locked the primer back into the closed position. No difference in RPM. 
Primer was nice and clean as were the two nipples (had the intake manifold off and checked carb and intake while there) and functioning normally.
Just an FYi. for you......


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## thill (Mar 5, 2014)

Pappy,
Thanks for the actual field testing! That's going above and beyond, for a guy you've never met. I really appreciate that!

I'll give mine a test run anyway, possibly tomorrow, if I can get time, but I'm guessing that I'll be back to checking for debris in the bottom of the bowl causing a fuel obstruction, and then replacing the main jet. Thankfully, both are easy to do.

Hopefully, I can find it immediately, now that I know what I'm looking for.

Thanks again. Will report back as soon as I do my testing.

-TH


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## Boat2fast (Mar 7, 2014)

You guys are having all the fun! Nothing around here but ICE.


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## thill (Mar 7, 2014)

I'm sure it's much colder up there, but snow and freezing rain is falling right now. At least the big lake here has open water to test boats on.

But you probably won't be complaining this summer, when it's 102* down here with 95% humidity.  :shock:


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## thill (Mar 10, 2014)

Update... Weather has finally moderated. Snow mostly melted. 
I finally got some free time this afternoon, so I snuck out back to play with the boat.

Opened her up and started by examining the primer system. Pulled and pushed on the primer, and noticed some fuel dripping/shooting out of the lower return hose underneath the carb. HEY!!! Sure enough, one of the tiny lower hoses that I did not replace last time had a CRACK in it. Could that be my problem? Don't know, but I replaced it.

Then I pulled the carb. Everything looked mostly clean, but there was a little powdery stuff here and there. Cleaned everything very carefully and reassembled. Replaced one other hose, just in case. Put everything back together, and still had an hour before dark. Just enough time to hit the lake. WAIT.... Put fresh gas/oil in the tank, with a shot of Seafoam, just in case...

In a rush, I forgot to bring my GPS. But the engine started up first pull and idled well, but a bit smoky. Maybe set a little rich? Or was it the Seafoam in the fuel, burning off carbon? Probably the latter. Nothing to worry about right now.

This time, I made sure I pushed in the primer back in all the way! She took off strong an got on plane. She ran all the way up to WOT, NO BOGGING at the high end! YESSSS!!!!! =D> =D> =D> 

By my ear, my RPM's still seem a little low, but NO bogging. THAT is what I would expect, if I needed to go down a little in prop pitch, but will have to check for that later. Ran around the lake until dark, then back on the trailer and back home.

So what was my problem? Moisture in the fuel? The crud in the carb? That cracked return hose? The choke handle being left out? Maybe all of them, but I really can't be sure. But I AM sure that you guys helped me out! *Thank you SO much for the help and suggestions! I really appreciate it!*

If I get time tomorrow, I'm going to bring the GPS and my new tiny tachometer, and take it back for more testing. Very curious to see what my revs are at WOT, and what the speed currently is at WOT. Will report back.

-TH


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## MDCrappie (Mar 10, 2014)

[url=https://www.tinboats.net/forum/viewtopic.php?p=344390#p344390 said:


> "]
> 
> By my ear, my RPM's still seem a little low, but NO bogging. THAT is what I would expect, if I needed to go down a little in prop pitch, but will have to check for that later.
> -TH



Tony - if you do wind up needing a prop I do have a like new 12". The 12" was a bit too small for my 16' and I went up to a 13".

BTW-so you don't knock your brain too much- this is Rob from Baltimore


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## thill (Mar 10, 2014)

Rob, 
Hey there!!! Good hearing from you! How are you? Still working in the same place? Every once in a while, I look at that prop and hope you are staying safe. 

I still owe you a fishing trip. I haven't forgotten, but I have not fished much these last few years.

The CCNP power plant has fish right now, but the harbor is probably is loaded up, too. I live on Lake Anna, and run down to Virginia Beach often, especially in May, when the big breeders are leaving the Bay. Let me know when and where you want to go, and I would be happy to host a nice trip.

This is the second time you have offered to save me prop-wise. That Turbo was perfect for my boat, once I lifted the engine a hole. But then it spun a hub, and not long afterward, my ECM went bad on that motor, and it's been sitting under the cover ever since. I plan to get her going this spring.

[email protected] is my email, (540) 219 - 9818 is my cell 

Talk to you soon.

-TH


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## MDCrappie (Mar 10, 2014)

Doin OK - going on 27. For the past 2 I've been inside, downtown, preparing for retirement. Will be sometime between this June and Jan '15 - we'll hook up when it happens. 
Haven't been fishing much this year yet due to the ice, but getting ready to start this week.


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## thill (Mar 10, 2014)

Yes, it's been a cold year. 

Hooked up my new mini-tach and hit the lake this afernoon, but I did a BONE-headed thing...

After hooking up the tach and mounting the display, I was so excited to go, that I raced off to the boat ramp (was getting dark) without putting the cowl back on.

Got to the lake and realized my mistake, but figured that it couldn't hurt too much... right?

She idled at 750-800 RPM in neutral, 650-700 RPM in gear. I think that was about right. Hit the gas, and she accelerated strongly. Stronger than the day before, it seemed. Almost screaming, actually. I looked over, and she was running 5710 RPM! I backed off to about 5200 RPM, and she sounded much better. 

I rode around like this for awhile, enjoying the scenery and the warm breeze. But when I slowed down a bit she did a lean-pop, which had never happened before. I sped back up, and all was well, but when I slowed, she lean-popped again, and cut off. Uh-ooh... What was going on? Why was she running lean? I tried to restart, but nothing. Pulled the primer once, and she started right up, ran well for a minute, then sneezed again. 

And that's when it hit me... without the cowling air was being forced down her throat, and causing her to run lean. NOT GOOD!!! What am I doing?!? I know better that this! I started up and she ran fine at idle, so I eased back to the ramp. Hopefully, I didn't do any damage.

Pulled the primer several times, and ran her a little rich, back at home, just to make sure there is a good coating of oil inside the motor. Will have to test her out soon. Will check compression first.

Boy, I'm really missing on this one!

-TH


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## MDCrappie (Mar 11, 2014)

[url=https://www.tinboats.net/forum/viewtopic.php?p=344505#p344505 said:


> thill » Mon Mar 10, 2014 9:00 pm[/url]"]
> 
> And that's when it hit me... without the cowling air was being forced down her throat, and causing her to run lean.
> -TH



Tony - I don't think this can happen, unless your fuel is being restricted. The more air going into the carb, the more fuel that will be drawn thru the Venturi. It will run better due to this increase, but I'm pretty certain the fuel mixture will stay the same. Otherwise wouldn't "ram induction" motors be blowing up all the time?


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## thill (Mar 11, 2014)

Rob, I really think it makes a difference. I noticed that when I got the lean-pop, I was heading into the wind. The carb is right there, catching the wind, no cover. Look:




But thinking about it, this would be a GREAT way to add HP to a small motor, if you could figure out which bigger jets to use. Force air in (like a supercharger) then add more fuel = VROOM. 

But my current jets are sized for the restricted and directed airflow presented by the cowl. Without it, I don't know... Maybe my mind has been poisoned. Over on BBC and on the hull truth, I've read how guys have scored cylinders and blown up motors by running them hard with the cowl and/or baffles off. And if I recall, they commented how much faster they were running... just before they blew.

I doubt if it's a fuel restriction, especially since she ran so hard at WOT. (Maybe a weak fuel pump?) And I really should have known better! The motor was screaming, and I was flying, and a little voice in the back of my head was telling me that something wasn't right. Then I looked at the tach, and it HIT me. DUH!!!!

I just went outside, and she doesn't want to idle for more than a few seconds, before a cough and she dies. I've got a bad feeling about this. 

My current plan is to add double oil to the gas, and try to keep her idling for awhile. Sometimes, the extra lube can smooth out very minor stuff in a cylinder, but if it's damaged, it might not come back. If I can get her running well, I'll take her back out on the lake with the double oil and see what happens. THEN I'll check compression. I'll report my findings.

-TH


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## MDCrappie (Mar 11, 2014)

[url=https://www.tinboats.net/forum/viewtopic.php?p=344547#p344547 said:


> thill » Tue Mar 11, 2014 7:59 am[/url]"]It would be great, with bigger jets. THAT might be a way to add more HP to a small motor. Force air in (like a supercharger) then add more fuel = VROOM!
> 
> But the current jets are sized for the restricted and very directed airflow presented by the cowl. I know that over on BBC and on the hull truth, guys have scored up cylinders and blown up motors by running them with the cowl and/or baffles off. And if I recall, they commented how much faster they were running just before they blew!
> 
> -TH



But the air is not being "forced in" under any "high" pressure. Any of those guys get "confirmation" on the air causing the explosion? My guess is that they were having problems prior, hence the reason for running w/o cowling.

I'd be fairly certain that the stock jet supplied with the motor is sufficient to supply the amount of fuel necessary for any "non-compressed" air flow amount coming thru that carb throat. 

I mean how much "pressure" is on that air when you're moving 25mph? I mean is it any (noticeably) harder for you to exhale while driving?


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## thill (Mar 11, 2014)

You must be online, as you were able to respond while I was still editing.

But you make a good point. I was doing about 25, and the wind was blowing maybe 10 MPH. So the air pressure was the equiv. of putting your hand out the window when driving 35 MPH. That is considerably more than with the cover on, but I hope you are right about the jets being enough to compensate

Going to run out to the lake right now. Will report back shortly. Thanks!

-TH


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## MDCrappie (Mar 11, 2014)

If you were getting the lean pop with the cover off, then put the cover on at home and now it's won't stay running you may have an exhaust leak. I had this happen to an old 40 I had.


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## thill (Mar 11, 2014)

OK, I'm back.

Went to the lake, and started her up. She popped, sneezed and shut off. Triple primed her, and she ran longer, then died. Hmmm.... Pulled the primer about six times and started her again. This time, she ran for awhile, then died. Good enough for now.

Long story short, I kept having to give her gas, but the longer she ran, the better she ran. After running her around for maybe an hour, she FINALLY stopped that "rattly" sound, and would idle properly again without sneezing. It still seems just a little "off", but it's much better than when I first started.

With the hood on, she ran up to 5,520 RPM, which is pretty perfect. Yesterday, with the hood of, she was passing 5700 by with no problem.


AND GET THIS... When loading up, I ran into an older gentleman ("Gary") with a home-made plywood racing boat behind his truck. It was quite the beauty! It had a 30 HP Mercury on the back, _without a hood to keep from restricting the air flow._ That caught my attention, so I asked him about it.

He says that 30 HP will run 8,000 RPM and push the boat up into the mid 60's. His 40 HP motor will run well up into the 80's, but he says he can't handle that anymore, at his age. He's about to turn 80. WOW. I got some pictures, but my phone is a pain to download from, so I'll do it later.

He was nice enough to take a look at my rig and give me some suggestions. In my case, do NOT run it without the hood anymore, unless I re-jet the carbs, and also put a 1/2" shim under my motor, to stop that spray from the front of the cavitation plate. 

Gary is a very interesting guy. Very glad I met him. Also glad my motor is running better.

After talking to Gary, my theory is that my motor was running lean, and it was getting dry inside the crankcase, which explains the rattly sound and the sneezing. Once the oil film got built back up, things are mostly back to normal. She's still not as quiet as she was two days ago, but I'll take what I can get.

-TH


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## Pappy (Mar 11, 2014)

Thill.....do yourself a favor at this point and check compression on both cylinders please?
OMC jetted engines to be able to run either with or without cowlings on all engines at any time....with the possible exception of some Military Spec engines that I am not familiar with. 
If this were not the case it would have been clearly outlined both in Owner Manuals and Service Manuals.......it is in none of the above and never has been. 
A lot of my troubleshooting time through the years has been spent running engines wide open with no cowl and no airbox on the front. Open carbs out in the breeze and in some wicked fast boats. 
Your RPM difference may have been due to the air temp difference as well as the open cowl since the large main air entrance is in the top rear and goes around a hot engine to get to the carbs. Or something else was going on. Between that entrance and the one below the carb there is no restriction whatsoever. 
When cowlings are developed part of the development sequence is to install a manometer in the cowl to check for restriction. 
I never experienced as much of a change as you have outlined. But the fact that it quit idling and slowly gained back idle quality the longer you ran it is not good. ........................So check compression.


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## thill (Mar 12, 2014)

It WAS strange... The motor was running great to start with. But the longer I ran it without the cowling, the worse it ran, to the point where it was sneezing and lean-popping and stalling. 

Then, the longer I ran it with the cowl back on, the better it got. That's why I was theorizing about the crankcase getting dry inside. Is there any other seal failure that could cause that?

When I get back this afternoon, I will check compression.

-TH


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## Boat2fast (Mar 12, 2014)

Pappy makes sense. Rule out compression problems first.

If my engine pops while throttling down, my first reaction is to richen up the idle screw. Looking at the picture of the engine, there doesn't appear to be an idle mixture screw. This carb has a bleed orifice. The size of the orifice determines the idle and off idle mix. Now assuming there are no air leaks from a crankcase gasket, bearing bleed tube, intake gaskets, or crank seals; the problem is most likely some crap in the idle circuit restricting fuel flow. If all that is fine, then an adjustment can be done by putting in a slightly smaller orifice to richen the mixture. The orifice meters air so a smaller one richens and a larger orifice leans the idle mix. First I would look for air leaks or dirt in the idle circuit. Possibly got a piece of crap into the thing with no cowl. I can get dirt in the face when my boat sits around for a while, first time I take off into the wind.


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## thill (Mar 12, 2014)

OK, I'm back.

Rob, I agree with your instincts. The lean pop started during high RPMs, as also did it at idle. I checked the cap on the gas tank, squeezed the bulb, and then opened the idle screw before heading to the ramp. Still sneezing, but it got me back. 

I just went outside to check compression. Bottom hole- 122#, top hole 122#. They were exactly the same, three checks on a row. Compression is good, thankfully!

There is an idle jet on this motor. It's set into the brass sleeve that you can see at the top left side of the carb. I had it set at 3 turns out, which is a little rich. (Book says 1-3/4 - 2-1/4 turns out) Rich enough that she smokes a bit at idle. I did this because I don't know the history of the motor, except that she set awhile. Set like that, she starts easily, and idles forever without stalling, and I'm sure she's getting good lubrication.

The fact that she STOPPED smoking at idle after the popping and stalling was a bit alarming. Then yesterday, when I first started her, and she was sneezing, I opened the idle jet up even more. Still no smoke. But the longer she ran with the hood on, the better she ran. And when I was loading the boat, she was smoking a bit again at idle. That was quite a relief to see.

Maybe some dirt did cause the problem. That would be one explanation that fits. Fortunately, it wasn't fatal!

-TH


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## thill (Mar 12, 2014)

Oh, almost fogot... Here are the pictures of Gary's race boat:












He told me that with the 30 HP Mercury, the boat ran in the 60's, but with the 40 HP, it went into the 80's. The throttle was a squeeze grip, and the operator kneels when driving, so that he can jump away, in case the boat flips.

This guy really knew his stuff regarding boats and motors. I learned a lot in a very few minutes of listening to him. I hope to meet him again.

-TH


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## MDCrappie (Mar 12, 2014)

Tony - the motor on my 16'er is a 1989-25hp Evinrude. I had a devil of a time getting it to run right when I got it. I cleaned carb, sync/link and got it running perfect, or so I thought. Got in the water and wouldn't stay running. Richen it up (had it 3 turns out), but still popping. Cleaned again, same thing. After 2 weeks of searching I realize I was leaking air at times. Wound up being the core plug right there next to the idle mix screw. Put a small blob of permatex on it and been idling/running perfect for almost a year now. 

Just had it out this morning. Caught 3 LM BTW.


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## thill (Mar 12, 2014)

Aaahhhh.... Now THAT was a good find! I just checked the schematics, and my carb is pretty much the same as yours, but with a different bowl. I see the core plug that you mention. Will probably just put a little stuff on it and all of the other seals. 

Hopefully, that will prevent this from happening again. Thanks for the tip!

Nice work on the LMB! I hope to be able to get out there sometime soon, not just boat-testing.

By the way, what kind of speed are you getting out of your 25?

-TH


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## MDCrappie (Mar 13, 2014)

[url=https://www.tinboats.net/forum/viewtopic.php?p=344768#p344768 said:


> thill » Wed Mar 12, 2014 8:41 pm[/url]"]
> 
> By the way, what kind of speed are you getting out of your 25?
> 
> -TH



I varies a lot. Basically I use the boat in 2 places. First place is 95% no wake. The other place is on the Suqy up close to conowingo dam. Depending on whether I'm going up or down river, and how strong the flow is will determine my speed. 

I haven't get run it WOT yet with the 13" prop (just got it last fall), but with the 12" I could get up to almost 27 by myself, or I even had it to 24+(not quite 25 on gps) with 2 other guys, one of which is over 300lbs, but this was downstream with a pretty good flow. I do have a rock guard on the motor, which I'm sure slows me down a bit.

When I'm out any other place I use my 20' Crestliner with 75hp. It's a perfect boat for anything except the Upper River

One other thing I did (not sure if it help or not) was put an additional "O" ring on the idle mix screw so that it couldn't vibrate and would seal out any air from leaking between it and the brass nipple.


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## thill (Jan 20, 2015)

Sorry for the late reply- I just saw your post. Thanks for the info. 27 sounds really good. That is what the Lowe ran before I sold it. Mine likes 23 MPH loaded the way it is. 

Well, it's been awhile, but all is well with my 25. I followed your suggestion, and sealed the plug on the carb with a little permatex. I also replaced all the primer hose lines and did the fine adjustments. It didn't change the way the motor ran, but was good peace of mind. Thanks for that!

This little motor runs flawlessly. I'm very happy with it. I have not run it with the cowl off anymore, but on some of the other threads posted recently, other guys are boring out intakes and running with the cowl off, and upsizing the main jets to get more HP. From a .067 up to a .070, I believe. Sounds like they are getting some nice increases, but me, I'm happy to leave my good-running engine alone!


-TH


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## thill (Feb 26, 2015)

Came across this thread, and figured I'd post an update.

The motor has run flawlessly every time I've used it. I hadn't started it since December, so I went out and pulled the primer and gave it a tug... She started on the second pull and purred like a kitten for a few seconds before I shut her off. (no water hooked up)

I have a very rich Seafoam mix in her, and that has worked great for me. Zero issues since I started doing that in all my small engines. Hopefully, Lake Anna will break up soon so I can get out. (It's solid ice mid-lake)

We just got another 5" of snow this morning. That makes 17" in the last 10 days or so! :shock: :shock: :shock: 

-TH


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