weird engine problem

[TikiDoc]

Here's a question for the engine gurus.  I've got an '83 140 Evinrude on my 22-2 project.  Premix/no VRO.  I had not run it in months, but I had run the gas out of the carbs last time I ran it.  Ran it this weekend off a 6 gallon tank with fresh gas.  Started easily and ran OK, maybe an occasional miss.  Once I put the cowling on, it acted like it was fuel (or maybe air) starved.  It would run, then die.  I could restart, but would have to increase throttle and push the choke.  It would rev high, then die again.  I tried to look for something being pinched by the cowling, but nothing was obvious.  Any ideas?

Thanks in advance,
Blake

[Aaron43]

Sounds like the base gasket, the gasket under the powerhead is leaking exhaust....run it with the cover off and see if it runs...

[TikiDoc]

Definitely runs with the cowling off.  How would one specifically test for a bad base gasket?

[flounderpounder225]

Long Shot, but if you knew any IH friends that could bring a CO detector you could run it with the cowling off and stick the detector down around the base gasket.  We use them at work for various pieces of equipment. 

[Aaron43]

Leaving the cowl cover off is how u test it....u need a new base gasket.

[futch13]

Check your cowling vent first.  Maybe a squirrel or mouse built a nest in it and shutting off airflow when cowl is on.

[TikiDoc]

Yeah, the vent was the first thing I checked.  Wide open.

[fitz73222]

I want to recap what you're experiencing here. The engine fires up and runs fine with the cowling off. When you put the cowling back on, how long does it take for the engine to start running bad and shut off? When you take the cowling back off, is there any evidence of exhaust smoke under the cowl? If the powerhead gasket was leaking that bad, you should be seeing water drips down the midsection from under the pan or brown exhaust ooze dripping down the mid. Any thing like that happening/
 

[TikiDoc]

I never tried to put the cowling on while it was running, but when I fired it with the cowling on, it would fire and run, but almost immediately die.  I will look tomorrow to see if I notice exhaust under the cowling.