Engine stalls leaving marina at forward idle

girraf

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Nov 13, 2016
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25
5.7L VP GL Motor and SX-M outdrive
Pretty regularly last summer, when motoring forward at idle speed leaving the dock, the engine speed will start to slow down and within a few seconds quit. It will usually start right back up with the key and then I add some throttle only to juice the engine and then it typically won't do it again the rest of the day so it must be a cold/cool engine issue. I normally run the motor on the muffs for a few minutes and idle at the dock for another 5 or so before pulling away for the day. I could probably workaround the issue by running the engine up at the dock to warm it up even more but would prefer to just not have the problem in the first place. Any ideas on what to troubleshoot for the issue? My guess is that its a carb issue but I haven't ventured into monkeying with the current settings. The channel to leave the marina is pretty narrow so losing my steering, even at idle speed is highly undesirable.
 

charleso

Petty Officer 2nd Class
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Nov 13, 2006
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Sounds to me like it could possibly be an issue with the choke if it's electric. The other thought is the ignition coil. Had one years ago in a truck that would stall about 10 minutes after you started driving. Tried several things, finally replaced the coil and never experienced the issue again.
 

wrench 3

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I'm wondering if maybe it's not warming up properly. A thermostat problem. Also after five minuets of idle the choke should be fully open. Mite be worth checking.
 

girraf

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Nov 13, 2016
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I do have an electric choke so maybe I'll do some testing to see how long it takes to fully open. Should I expect that the choke to be fully open by the time I'm motoring out? Is it bad to get underway before it open fully?
 

Bondo

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Ayuh,.... Welcome Aboard,.... Sounds like it's runnin' outa gas to me,....

How long has it been since ya check the fuel filter's contents for crud, 'n changed the filter,..??

The electric choke oughta pull off in a few minutes, 'n No it shouldn't bother with motorin' outa port,...
 

Senior B

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May 19, 2006
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What is your idle RPM in gear in the water? I would shoot for at least 650. I found on my carb boat that an idle rpm of just under 800 in Neutral worked out to 650 when in gear in the water. Sounds like your doing reasonable prep by doing a quick run on muffs before you leave the house and warming up at the dock. Electric chokes open up pretty fast so it should be open all the way in 5 min or so. It doesn't hurt anything from a damage perspective to go if it's not.
 

wrench 3

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I was thinking that the choke may be staying on after the engine has warmed up and loading it up with fuel. That, or the coolant thermostat is bad and the choke is off but the engine is still cold.
 

girraf

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Nov 13, 2016
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Fuel does make sense given the symptom. Iv got a new fuel filter to install before the season begins. Now that I'm thinking again, this problem happens on the trailer too. When running on muffs, if I just let the engine idle, after about 30 seconds, the idle will slow and eventually stall if I don't give it throttle. my suspicion is the engine is loading up with fuel and bogging out slowly. If it were the other way and the mixture was getting too lean, wouldn't I get a momentary increase in rpm just before the motor quit? If the ending is getting rich, is there a way to make an adjustment for that or should keep on the throttle a little bit when the engine is cold?
 

Bondo

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When running on muffs, if I just let the engine idle, after about 30 seconds, the idle will slow and eventually stall if I don't give it throttle. my suspicion is the engine is loading up with fuel and bogging out slowly.

Ayuh,.... If that's the case, the spark plugs will be black with soot, 'n probably wet with gas,...
 

girraf

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Nov 13, 2016
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This is only my first year with the boat and so I don't yet have a good baseline on how all the components stand in terms of life limit like spark plugs. Probably should pull them and inspect at some point. Same with the manifolds and risers, but the previous owner did as he inspected and they pressure tested good. The engine otherwise hums along nicely at cruise power and no complaints with it. Steady watertemps around 150/160.
 

wrench 3

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should keep on the throttle a little bit when the engine is cold?

A marine engine doesn't have a fast idle system. so you need to idle it up manually when cold. But after five minutes it should idle on it's own.
 

Lawnpro979

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Aug 17, 2014
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Is this a Holley carb? If so what's the list number....sounds like the idle mixture needs to be adjusted.....it's not that difficult as some YouTube videos show...
 

girraf

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Nov 13, 2016
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Pretty sure it is a Holley. 2 bbl for sure. Don't have the part number at the moment. Now that I'm the proud owner of a vacuum gauge, I'll be able to play with the idle settings and actually do it properly. Maybe I just need to set it slightly higher, although I don't want to go much because my idle forward speed in the waters is pretty much where I want it.
 

Lawnpro979

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Aug 17, 2014
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There's a process for setting it....take your time, it can take a while, when I set mine, "after a card rebuild" I didn't have a vac gauge, did it by rpm's I was surprised that mine worked best at like 1 and a quarter turns. Again there's a lot of YouTube videos out there to help.
I had hard starting 10 year old boat, the carb had never been rebuilt, I was shocked at how easy it was and the diffrance it made.
Best of luck
 

Lawnpro979

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Aug 17, 2014
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Sorry, not the idle speed but the idle mixture......there's two screws on each side. They need to be adjusted together. These screws are only for the idle mixture.
You will adjust them at the highest idle possible, then set the idle screw speed.....
 
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