85 Invader OMC Cuts out but runs fine with Engine lid open

[mack111]

Just bought 85 Invader OMC 2.5. Ran fine but engine cut out at high RPM's. Partner thought it was a blown head gasket so we took head off and sure enough the gasket between #3 & #4 was blown. We replaced the gasket but we still had same problem---the engine will not stay running unless we open the engine lid and give the motor more air, then it runs fine! We were told we may have a leak in the exhaust manifold. Does the manifold have to be magnifluxed to find the leak, or should we be able to spot it ourselves?

 

[Levinz11]

Re: 85 Invader OMC Cuts out but runs fine with Engine lid open

Do you hear a tick tick tick from the manifold?

 

[mack111]

Re: 85 Invader OMC Cuts out but runs fine with Engine lid open

Do you hear a tick tick tick from the manifold?

Thougt I replied to this but it didn't post. Yes, I think I hear a ticking noise. Partner doesn't hear it. What's the ticking mean?

 

[Maclin]

Re: 85 Invader OMC Cuts out but runs fine with Engine lid open

Could be exhaust leak, I think that is what Levinz is aiming at. In boats with small enclosed engine comparments even a small exhaust leak can pollute the available air enough to affect combustion.

 

[mack111]

Re: 85 Invader OMC Cuts out but runs fine with Engine lid open

Could be exhaust leak, I think that is what Levinz is aiming at. In boats with small enclosed engine comparments even a small exhaust leak can pollute the available air enough to affect combustion.

OK, I'm leaning in that direction now too. Anyone know of the compound that you can buy that detects leaks in heads and manifolds? I read about it recently in a car mag but can't remember what it was called.

 

[Jammer864]

Re: 85 Invader OMC Cuts out but runs fine with Engine lid open

With a cold engine, you can use soapy water in a spray bottle. Look for the bubbles or fizz.

 

[mack111]

Re: 85 Invader OMC Cuts out but runs fine with Engine lid open

My partner tried that and said he saw no bubbles. From reading other threads I learned also that the manifold should be able to be touched when running. Ours is Hot and cannot be touched with a bare hand. Possible water pump problem?

 

[bonzoscott]

Re: 85 Invader OMC Cuts out but runs fine with Engine lid open

You need to pull the manifold and check for rust blockage in the water passage. That would be likely causing the hot exhaust. You need to address the exhaust leak as well, so a good time for a new gasket. Running the boat motor on muffs or in the lake, pull the hose at the thermostat and check for good water flow. This will tell you if your sea water (impeller) is operating.

 

[mack111]

Re: 85 Invader OMC Cuts out but runs fine with Engine lid open

You need to pull the manifold and check for rust blockage in the water passage. That would be likely causing the hot exhaust. You need to address the exhaust leak as well, so a good time for a new gasket. Running the boat motor on muffs or in the lake, pull the hose at the thermostat and check for good water flow. This will tell you if your sea water (impeller) is operating.

Ok, thanks. The exhaust elbow looked a little rusted to me but partner didn't think it would affect anything. Also, the outside two runners (at each end of the manifold) look a lot darker than the 2 inside runners, almost black.

 

[mack111]

Re: 85 Invader OMC Cuts out but runs fine with Engine lid open

We found the problem. There is an exhaust/intake? port on the other side that is capped off with a 5 or 6 inch rubber boot. The boot had a huge tear in it, making the engine suck its own dirty air. We replaced the boot with a part we got at Home Depot and now the boat runs great! Thanks to all who helped on this.