Ski Boat engine dies when cover is closed

[bill29456]

I have a ski boat with a 351 inboard (commander) engine with a velvet driect drive transmission. I have an odd problem. When the engine cover is lifted it idles perfectly. As soon as you close the cover over the running engine it starts to drop in rpm off idle and then dies. If you open the cover before it dies it will recover and idle all day long. I changed out the carb for a new one. I then thought it might be a vaccume leak, so i changed the intake gaskets..and its still happening when the cover is closed. I have tried tapping on wiring and can't find anything to cause the idle to drop. I replaced the pcv valve. I even disconnected the throttle cable so the carb was not hooked up to any cables..just the fuel line...and it still started to stumble after the cover was closed. Yes the air cleaner (spark arrester) has been cleaned. I have a big 8" access port in the floor to tighten the ski pylon, and have even tried it with the port cover off, still tries to die when the cover is closed.
Any ideas????

Bill
Ladson SC

 

[a70eliminator]

Re: Ski Boat engine dies when cover is closed

Could it be that you have a big hunk of loose insulation on the roof of your cover thats being sucked down over the carb.

 

[Coors]

Re: Ski Boat engine dies when cover is closed

Your blower is running? you do have 18 square inches of space open to the outside of the doghouse for intake , and more for exhaust (air circulation)
It sounds like you don't.

 

[freddyray21]

Re: Ski Boat engine dies when cover is closed

If it just started this then it's probably not the clearance on the doghouse, but an exhaust leak. the blower on should help that, but you still need to fix it.

 

[bill29456]

Re: Ski Boat engine dies when cover is closed

Thanks for the replies. The inside of the engine cover is just fiberglass. As for the exhaust leak...will that cause the engine to stumble off idle and die? I do have some leaks from the exhaust manifolds to where you can hear the valves ticking, but i never thought it would cause an idle problem. I'll pull the manifolds and see whats up.

Bill

 

[Coors]

Re: Ski Boat engine dies when cover is closed

You have several problems.

 

[freddyray21]

Re: Ski Boat engine dies when cover is closed

a motor needs air to run. Exhaust does not have enough air left in it to run the motor. I tinker with outboards and run them in a barrel and if I don't have a breeze or a fan running the exhaust from them will kill the motor with a cover off of them.

 

[bill29456]

Re: Ski Boat engine dies when cover is closed

Well i pulled hte exhaust manifolds off and all the gaskets were blown out at the top. I'm starting to think it was dumping exhaust upwards killing the idle for lack of oxygen. I'm having the flanges checked for flatness and if they are bad...having them shaved flat. Does anyone have suggestions for a high quality exhaust gasket?

Bill
Ladson SC