Exhaust in engine compartment

[Daphne444]

I have a 1990 90HP Force outboard on which I just changed out a couple of pistons based on Frank's great instructions. It runs great at full throttle, but I am having some trouble getting the idle set so that it does not stall when going into gear.

As I was trying to adjust the idle speed on the water I noticed that I was getting exhaust into the engine compartment both in neutral and in forward (I did not notice this on land with the muffs). Since I am running double oil to break in the new pistons the smoke makes it pretty easy to see. The idle relief bellows appear to be in good shape with no splits that I can tell. It looks like the exhaust is bubbling up from the bottom of the engine compartment in the midleg. First question, should there be water down there in the midleg? The water drains out when I take the boat out of the water, I'm just not sure if it should be totally sealed or not. Any guesses as to how the exhaust might be bubbling up through the water and into the engine compartment?

Thanks

 

[Frank Acampora]

Re: Exhaust in engine compartment

There is a soft rubber gasket around the midleg down near the bottom of the shroud. Sometimes it tears and CAN (not definitely will) let exhaust up into the engine compartment. Obviously, this will only happen when the engine is sitting low in the water. This gasket goes completely around the midleg and is a royal pain in the butt to replace. You need to disconnect the lower engine mount, remove the rear shroud, remove the old gasket and glue in the new one. If it is only torn on the rear portion, you can try cutting and replacing only the torn section--that way there is no disassembly required except the removal of the rear shroud

And yes--when the engine is sitting low in the water, there will almost always be water inside the rear shroud. Some of them have weep holes to let out the water faster, some have them plugged. It seems to have depended on the whim of the factory and the phase of the moon.

 

[Daphne444]

Re: Exhaust in engine compartment

Thanks Frank. While out on the water last weekend I was pretty sure that it was bubbling up through the gasket area you are talking about, I will have to double check. The portions of the gasket I can see appear to be in OK shape, but I guess I will have to take off the rear shroud and take a closer look.

Although I suspect that it is torn, I hope not. From your description it seems that replacement of the gasket might be beyond something that I can do.

thanks

 

[Frank Acampora]

Re: Exhaust in engine compartment

It is not beyond you or the average owner. It only takes hand tools. Twelve 1/4 inch bolts to remove the rear shroud and four 5/16 bolts to remove the lower engine mount cover. Then just yank back on the engine leg to make clearance to get the gasket around the front. The problem is it is time consuming and frustrating if you elect to replace the whole gasket. It does help (your state of mind) to know the proper cuss words to use on the engine.

And if you are female, as your forum name implies, please use the correct music with the words. (for those who don't know, that is an allusion to a Mark Twain quote.) GOD! My brain is so full of useless trivia that it just SPEWS forth unbidden.

 

[Daphne444]

Re: Exhaust in engine compartment

Frank, thanks for the information. I took the rear shroud off (easier said than done: 2 broken bolts with lots of corrosion). The gasket is clearly split in the rear, but is appears to be in pretty good shape on the sides and front. It is split along the middle as the first picture shows, I suppose that I cannot just glue it back together and will have to get a new one.

Another question, after I got the shroud off I saw a small tube in the idle relief bellows which looked curious, second picture. Upon closer inspection it appears that it is just laying in there not connected to anything. I took it out and took another picture, third picture. Any idea what it may be? Did it come from somewhere else in the engine?

Thanks

 

[Frank Acampora]

Re: Exhaust in engine compartment

That is one of two tubes in the idle relief system. it has worked loose and worked its way into the bellows. In playing around with mine, it fell into the midleg--so there it will stay. Even the factory manual (which shows them) does not explain exactly where they attach or how they attach. And I have never taken apart one of these midlegs, so I can not say where they come from. In the schematic, it looks like they insert into the match plate below the engine. But at any rate, my 125 runs well without it (them) so if you want to remove it or leave it out, do so.