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HELP - 1983 Model 350's stalling when hot

T

truk911

New member
I have a boat neighbor with the same model boat I have, his is a 1983 and mine is a 1985 36 AFT Cabin Carver both with T-454, Model 350’s. My neighbor is having a problem with his engines stalling when hot. He leaves the slip no problems and the engines are running fine, idles out of the harbor and out onto the lake, both engines run great at cruise and WOT all day long. When he returns to the harbor and brings the engines down to idle, either engine or sometimes both, die at idle. They will start back up, but unless he brings up the RPM's they will die again. He has been having this problem for 2-3 seasons off and on. They are open cooling and have electronic ignition. He has recently replaced the cap and rotor without any noticeable change. It’s the same problem with both engines without any rhyme or reason to it.

Any suggestions where to go next?
 
Wild guess, but try running the blowers after the long day of running. Maybe vapor lock due to high engine compartment temps. Make sure the blowers move enough air to get the temps down noticeably.
 
Sounds to me like a bad idle mixture setting on the carbs and, since both of them do this, I assume the same mechanic adjusted both carbs.

Note: Properly adjusting the idle on a marine engine is much harder than most people realize since the motors don't conveniently rock back and forth on their mounts if the idle mixture is off. Also, it's hard to hear the exhaust in the bilge.

Try this: Find a vacuum source (NOT the PCV valve hose) and hook up a vacuum gage. Warm the motors thoroughly. then idle 'em down and dial the mixture screws to achieve maximum idle speed. Finally, add 1/4 of a turn CCW on each adjustement screw. And make damn sure the chokes are wide open before you begin!

Jeff
 
in addition to the previous two posts, the float/needle/seat could be marginal inducing a rich state.

also, the default q-jets, especially on big block applications are not setup in an optimal manner. enabling the bypass idle air circuit is usually a prudent step to fixing this.

A final point to consider - fuel composition has changed a lot since these engines were delivered...would be prudent to bring the tuneup specs used to the current factory recommendations.
 
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