120 Force outboard exhaust problem

[afdcaptain]

Ok lets try this again with a little more information. I have a 1994 Bayliner Capri 1700 with a 120 hp outboard force. The boat was my dads. The lower unit went bad. He purchased another lower unit for it. On the original lower unit the exhaust came out through the middle of the prop. The lower unit he purchased the exhaust comes out a v nothch type thing above the prop. The Mercury dealer said it didnt matter and would still work. The boat ran fine before this happened. Now that they have installed the lower unit on it it will not run with the cover on it. Take the cover off and it runs fine. put it back in and it will stall. I think it is due to exhaust fumes choking the carbs out. My question is, is there something at the lower unit that they could have done such as tore a gasket or something that is the problem.

[Frank Acampora]

Force did make the 120 in two versions: the single exhaust and the dual exhaust with through prop exhaust in addition to the snout.

It should not make a difference running which lower unit is used. If exhaust is filling the cowling and killing the engine, the first place to look is the idle relief exhaust bellows below the head. It is black rubber and connects to the two holes in the back of the shroud where water comes out. It may have a tear or may have been displaced from the tapered seat. Either reset it into the seat or repace it if it is torn or has a hole.

NOW: having said that, I have an engine on which I ran a single exhaust lower unit. I replaced that with a dual exhaust lower unit and a perfectly fine running engine now gives me problems. At this point I won't specifically blame the lower unit change, but I am suspicious. I am not happy with the engine performance and I will be changing back to check on that.

SO: While the single exhaust should work properly on your engine, there is a chance that is may be contributing to part of your problem. But, before jumping to confusions, check the idle relief exhaust bellows.

[foodfisher]

How about that big donut seal in lower leg?

[afdcaptain]

I think I am going to take the lower unit off and see what I can find. If a gasket is tore or what

[Frank Acampora]

More than likely you will be wasting your time. There are no gaskets visible from the removed lower unit. But hey! You might find something else.

[afdcaptain]

Any other ideas because it ran fine until they installed the bottom end.

[Jiggz]

Force did make the 120 in two versions: the single exhaust and the dual exhaust with through prop exhaust in addition to the snout.

It should not make a difference running which lower unit is used. If exhaust is filling the cowling and killing the engine, the first place to look is the idle relief exhaust bellows below the head. It is black rubber and connects to the two holes in the back of the shroud where water comes out. It may have a tear or may have been displaced from the tapered seat. Either reset it into the seat or repace it if it is torn or has a hole.

NOW: having said that, I have an engine on which I ran a single exhaust lower unit. I replaced that with a dual exhaust lower unit and a perfectly fine running engine now gives me problems. At this point I won't specifically blame the lower unit change, but I am suspicious. I am not happy with the engine performance and I will be changing back to check on that.

SO: While the single exhaust should work properly on your engine, there is a chance that is may be contributing to part of your problem. But, before jumping to confusions, check the idle relief exhaust bellows.

Frank,
I just happen to be looking for a replacement for the exhaust rubber bellow you mentioned, do you know the proper name or maybe a link where to purchase one? Thanks.

Jiggz

[Frank Acampora]

I don't know the exact description but if they don't sell it here at iboats, try **********. And use a plastic zip tie to attach the new one. The original metal clip did tend to bite through the rubber.

[Jiggz]

Frank, thanks! I got it. It's named boot idle exhaust! You're right the original wire clamp tend to cut through the boot itself which is the reason I have idling problem when the boat is in the water but runs smoothly on "flushing muffs". I've since replaced it with a stainless hose clamp but the damage is done and the boot is terribly leaking exhaust. Thanks again.