Mercruiser AlphaOne 3.0L/LX Stalls on Idle

SDJ_2016

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I have Mercruiser AlphaOne MCM 3.0L / LX I/4. I had some bad gas in the tank that gummed up the Carb. Drained the gas, had the Carburetor rebuilt, replaced the plugs. The engine now starts everytime and runs real well at high to medium throttle.

When I pull the throttle back to idle, which I would do to put it in gear, the engine stalls, fairly quickly I might add. Can't seem to get it to run at less than 1950 RPMs. 2000 RPMs and up, runs like a champ.

Any ideas on what might cause this? IAC, Fuel Pump, Fuel Filter? 1994 build. Any suggestions will be great as the backup at the maintenance ship is 6-8 weeks (So much for summer)
 

alldodge

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Do think a 1994 build 3.0 would have a IAC, but lets prove me wrong with a serial number of the motor????
 

SDJ_2016

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I am skeptical there is an IAC. Engine Serial is 0F152855. Clues and suggestions are most welcome.
 

alldodge

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I meant to say, I do not think a 94 3.0 would have an IAC
Bringing up the serial number, its a Merc carb motor

https://www.mercruiserparts.com/3-0l-gm-181-i-l4-1990-1994-0c856559-th

Take the fuel filter off and upon removal note if its full (it will spill a tad) or if its below full

Pour contents into a clear container and see if there is only clear gas

If filter was full then all good, then its time for a carb rebuild
 

SDJ_2016

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Thanks for tip, will pull fuel filter off in the morning and check. Carb Rebuild already done.
 

SDJ_2016

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Finally got a break in the heat to change the Fuel Filter. There was some gunk in the bowl. Cleaned that all out, new gasket, filter, spring. Engine fired right up and purrs fine. Same problem as before: Engine starts easily, runs smooth and consistent at 2100 RPMs. When I pull the throttle back to neutral, the engine dies quickly.

Tank of Bad Gas: Drained tank, Rebuilt Carburetor, Changed Fuel Filter, replaced Spark plugs
Now the engine won't run while in Neutral.

I am ready to hand it off to the Marina at this point. Their backlog is down to 8 weeks.... LOL. So much for summer boating. Any ideas would be helpful?
 

alldodge

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Have you tried to increase the idle stop screw on the carb to increase the idle rpm?

Run the idle mixer screws in real easy then back out 2 full turns?
 

SDJ_2016

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Good Suggestion. I had tried the idle screw at 1.5, 2 and 2.5 turns and it did not seem to make a difference. The screw was set at 1.5 prior to the carb rebuild. Would the engine just die like it is doing or would it run rough if the idle screw needs fiddling.

Are you suggesting I keep cranking the screw out incrementally until I can get it to run?
BTW. Thank you alldodge for the help here, much appreciated!
 

alldodge

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Scratch that, you said in first post unable to get it to idle less then 1950 rpms

If compression and timing are good, then carb needs to come apart because the idle circuits are clogged
 
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