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Stumbles at idle in gear

D

Dennis B.

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"1986 LM318 (76 LUHRS 280&

"1986 LM318 (76 LUHRS 280) am having trouble with stalling at idle. Only happens after engine has ran for at least an hour at cruise. RPM under load is 650-700, idles great out of the creek. Out for a short ride and back it will stumble or lopes at idle. Slight throttle move and it wiil seem to miss. All fuel filters,fuel pump are new,cap,rotor and coil are new,plugs and plug wires are new. Also replaced Q-jet carb with Holley but problem still there. I have even transfered all fuel out and put in fresh fuel. This problem started before I did all the parts listed"
 
"Sounds like you need a good c

"Sounds like you need a good carb man to 'super tune' that thing. You'd be surprised at how difficult it is to get a hard-mounted marine engine's carb properly adjusted! (They dont rock and roll like a car engine on soft mounts.) I use a vacuum gage to find the highest vac reading, then add a titch of idle mixture rich.

Jeff"
 
"Jeff, I can relate the tuning

"Jeff, I can relate the tuning issue to the Q-jet carb. The holley is my back up carb,ran early in the season until I had the Q-jet rebuilt.Problem started weeks after rebuild, tried to dial in but after good run it's the same stalling issue. Switched back to the Holley that ran perfect but problem still there.I am leaning towards a problem in the distributer since it only happens after 3100rpm run for cruise. Thinking advance is hanging up and not pulling in at slow speed. Is a newer Mallory electronic,will try and remove for better look at springs and wieghts."
 
"Just to summerize what is goi

"Just to summerize what is going on with my motor. Distributer was the problem, Mallory electronic module was breaking down after heating up. This is a magnetic pick up, replaced with new and installed a spike protector ( also by Mallory). Finally went out tonight and boat ran great, had to advance the timing slightly to get full rpms."
 
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