3.0 stumble stall when cold, great when warm

Oldpos

Petty Officer 2nd Class
Joined
Jun 16, 2019
Messages
112
i have a 90's 3.0l mercruiser engine with electronic ignition that stalls when throttle is advanced after i first start it. it starts first try everytime, idles great,but when i push the trottle above 1000rpm its stumbles then stalles for about 3 tries then when i advance it very slow it will build up rpms and run correctly, once i get it to run wot it will accelerate off of idle perfectly every time. if i sit and float for an hour or two the problem will happen again. timing is set correctly, compression is good. it idles between 700 to 800 rpm, WOT with 15deg prop is 3900 ( may to adjust linkage for more rpm, just changed prop from a 13 deg). this is on a 24 ft pontoon.

im not sure if the accelerator pump , or choke would cause this, or am i way off ? any idea's how do i check if its an accelerator pump? how to check electric choke?
 

alldodge

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Mar 8, 2009
Messages
42,555
once i get it to run wot it will accelerate off of idle perfectly every time. if i sit and float for an hour or two the problem will happen again.

Either to much or not enough fuel. I'm leaning toward not enough, and the accelerator pump

Choke should be straight up and down when warm

Accelerator pump should squirt fuel into the carb when the throttle is pumped

Look down the throat of the carb when motor is warmed up, see if fuel is dripping after motor is turned OFF
 

Bondo

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Apr 17, 2002
Messages
71,083
Ayuh,..... I'm with AD,.... sounds like it's lackin' good fuel flow,......
 

Oldpos

Petty Officer 2nd Class
Joined
Jun 16, 2019
Messages
112
I took it out again yesterday, i wanted to try and adjust the carb under load as it won’t do it on the hose. It actually got worse, basically it runs at idle then stalls and sitters until I get to wot, also had crap luck my started sheared the outboard mount bolt so it wouldn’t engage the flywheel, thankfully we were loading it up for the day and it happened at the dock. Had to pull the engine today to get the rest of the bolt out. Last time I use the grade 5 hardware that came with the starter! I went back grade 8.

anyhow I went and got a carb rebuild kit from the local boat place and they said it’s probably the fuel pump not regulating, holy crap $179 bucks for a pump!!!
 

Oldpos

Petty Officer 2nd Class
Joined
Jun 16, 2019
Messages
112
I took it out again yesterday, i wanted to try and adjust the carb under load as it won’t do it on the hose. It actually got worse, basically it runs at idle then stalls and sitters until I get to wot, also had crap luck my started sheared the outboard mount bolt so it wouldn’t engage the flywheel, thankfully we were loading it up for the day and it happened at the dock. Had to pull the engine today to get the rest of the bolt out. Last time I use the grade 5 hardware that came with the starter! I went back grade 8.

anyhow I went and got a carb rebuild kit from the local boat place and they said it’s probably the fuel pump not regulating, holy crap $179 bucks for a pump!!!
 
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