Engine stalls when cover replaced on Yamaha T9.9exrw 1998

[Spiedeg]

Problem
When I put the engine cover back on and seal it locked the engine rpm reduces from a 1000 rpm idle to about 400 rpm, sometimes staling. This is an immediate reaction of less than 30 seconds.
What I have tried so far.
The Carburetor has been totally disassembled, all parts ultrasonically cleaned and a Yamaha rebuild kit installed. The electrothermal choke has been tested and found functioning normally.
One outboard mechanic?s first comment was that I have a hole in the gasket that is in between the power head and the exhaust and that the carbon monoxide is starving the motor.
Request
Can any one tell me exactly from where carbon monoxide could enter the engine cavity that is enclosed by the engine cover.
Has anyone experienced this problem or would anyone be able to direct me to illustrated diagrams of the parts that make up the over all exhaust system.
If there are already posts on this subject please list the names so I can refer to them.

Thanks so much
Spiedeg

 

[MARV1]

Re: Engine stalls when cover replaced on Yamaha T9.9exrw 1998

Airflow restriction in cover, air goes in by grab handle in rear, check for restrictions.

 

[Spiedeg]

Re: Engine stalls when cover replaced on Yamaha T9.9exrw 1998

Thanks for your responce.
I looked at that first thing and there are no restrictions. I even concidered running a tub from the carb intake through the breather hole in the cover so that the engin would be sucking air that i know is clean.
I still suspect carbon monoxid leak but dont know how it would be getting from the exaust tube into the arie under the engin cover where the carb mouth is.