I have a 90hp merc, 2001. It was really bogging down and dying in the spring.I took it to the mech. and he tuned and cleaned the carbs. It starts great now and runs great. Just if I run it for a long period of time at top speed she starts to cut out and stumble when heading back in. If I slow it down and cruise at 10-15 it stops stumbling and makes it in without cutting out. The mech. said everything was good, compression etc.... He did use a external tank to run it as i didn't put gas in it before I took it to him. Also, if I have a full tank, to the top, it won't do this. Its only after I run a full tank two or three times.

thanks cd

No takers huh? Im guessing tank or something simple , just don't know where to start.

This is one time that I would change the plugs and swap the coils around. Sounds crazy but not all cylinders fire with exactly the same requirement of spark. And mostly, there may be an ever so slightly more resistance in one plug than another as well as in a coil. Make sure you are using NGK. and even at that. Don't assume that they are perfect, OHM each one and use a hair dryer to heat each one while on the bench. Then retest. I would like to see the pluges get to at least 140degrees for testing. That is just about max for a hair dryer.

Thanks,
I ll give that a try. Thanks for the response Mike.

CD