Idling problem with engine cover on......help?

NorthportTroller · Jul 14, 2009

Force 35 H.P.
Model # 357P9A
Serial # 1012
US Marine Power
Hartford, WI
2 Cylinder
Cross Flow Induction

Engins has ran great until a few weeks ago. Idle started deteriorating. Will idle cold start, once it runs a little, it starts to stall. Getting pleny of fuel. There seems to be a problem with a possible exhaust leak inside the cover, because when I take the cover off it runs fine, but when I put it back on it will start to idle down and get rough and stall.

I can barely see a litlle smoke inside when the cover is off, it's not a lot. I checked the intake on the cover and it is free and clear. It is very hard to see where the leak is coming from, if any.

I tightened up some bolts here and there on any panels that had gaskets on them, and it is still running funny just with the cover on, at idle. Other than that it runs great.

moparman · Jul 14, 2009

Re: Idling problem with engine cover on......help?

NPT, I know the larger motors have an exhaust/water sleeve inside the cowl to allow exhaust pressure to bypass the lower exhaust outlet when idling.When you are at idle or slow speed,there isn't enough exhaust pressure to over come the water mass at the lower foot exhaust ,so it gets routed to the top to exit along with cooling water.I'm not sure if your's has it ,but if so it should be located at the rear of the power head going to the rear of the lower cowl. hope this helps ,keep us posted. MOPARMAN

timdan94 · Jul 14, 2009

Re: Idling problem with engine cover on......help?

I have an 85 hp and had the same problem. I replaced that rubber exhaust boot and the problem went away.

NorthportTroller · Jul 14, 2009

Re: Idling problem with engine cover on......help?

moparman said:
NPT, I know the larger motors have an exhaust/water sleeve inside the cowl to allow exhaust pressure to bypass the lower exhaust outlet when idling.When you are at idle or slow speed,there isn't enough exhaust pressure to over come the water mass at the lower foot exhaust ,so it gets routed to the top to exit along with cooling water.I'm not sure if your's has it ,but if so it should be located at the rear of the power head going to the rear of the lower cowl. hope this helps ,keep us posted. MOPARMAN

Good stuff bro, but I don't think so. The upper exhuast port on this size engine is located on the rear center of the driveshaft housing and is open and freely spouts out ehauxst and water at idle. It is acting as it is running out of fresh air after I install the motor cover.

NorthportTroller · Jul 14, 2009

Re: Idling problem with engine cover on......help?

timdan94 said:
I have an 85 hp and had the same problem. I replaced that rubber exhaust boot and the problem went away.

Curious, where ids this boot located, I did not remember seeing one....??

timdan94 · Jul 14, 2009

Re: Idling problem with engine cover on......help?

does your engine have these holes on the back of the midsection like the ones in red?

NorthportTroller · Jul 14, 2009

Re: Idling problem with engine cover on......help?

Yes it does.

moparman · Jul 14, 2009

Re: Idling problem with engine cover on......help?

if its got those holes ,it should have the exhaust boot on it . look again and see if you can see where the holes come out in the back of the cowl.Also you may want to check the seal/gasket for the power head to lower unit .keep us posted. hope this info helps. MOARMAN

NorthportTroller · Jul 15, 2009

Re: Idling problem with engine cover on......help?

Nope, no boot on here. It's just the power head bolted right to the leg. Looks like there is a base gasket? Is that hard to replace? There is also another gasket on a plate on the side of the crankcase. That was dripping water, but after I tightened it, it stopped, but I still have a a small exhuast leak somewhere in the back of the power head, I can see a little smoke, but not where it is coming form. If i get it to idle, and then put the cover on, when it starts to stall, i pull the cover back off and all this smoke comes out.

timdan94 · Jul 15, 2009

Re: Idling problem with engine cover on......help?

Look down inside the back of the cowling right about where those holes come out the leg. There should be a black accordion looking rubber boot that connects to those two holes.

NorthportTroller · Jul 15, 2009

Re: Idling problem with engine cover on......help?

Na buddy. Just the power head bolted to the bottom of the lower cowl, no bellows. Do I have to yank the power head to see it? Maybe this smaller HP enginge is different than what you are saying. Here is a pic.........

moparman · Jul 16, 2009

Re: Idling problem with engine cover on......help?

IF this is an 1989 model, it will have a gasket between the power head and lower leg. This model does not have the rubber boot/sleeve as the bigger motors do.This motor has an exhaust passage way cast into the lower leg,that is sealed to the upper power head exhaust outlet via the powerhead to lower leg gasket. This is most likely your exhaust leak. Same problem as we described before, just different way of doing it. Hope this helps you with your problem,and keep us posted on your repair. MOPARMAN

NorthportTroller · Jul 16, 2009

Re: Idling problem with engine cover on......help?

Yes, I agree. Is that very difficult? I am a backyard mechanic, just wondering what kind of time is involved. Also, I looked for this gasket on Crowley Marine and they don't have that gasket availiable. Any tips on where I can find that. I also want to replace the side exhaust cover gasket and put a new needle in the carb.

NorthportTroller · Jul 16, 2009

Re: Idling problem with engine cover on......help?

Guess what I found? A little thing called an idle adjustment screw! Hahaha. Frigger was pretty hidden, but I found it, and it made a huge difference!

However, I still have an exhaust leak under the cowl, and I found it. It is on the side exhaust cover where the water once leaked!

Amazing what a digital camera and led light will show ya. Gonna try to fix this gasket redneck style, make one. I'll let ya know. Thanks so much for all the advice pals!

(Note the the hidden screw above the intake hole and the burn mark under the side cover from the exhaust leak!)

Idling problem with engine cover on......help?

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