Merc 5.7 stalls after cruising

[AShipShow]

Hi all,

I have recently just splashed my 3 year long restoration of a 96 Bayliner with a 5.7L Merc with a 2bbl Mercarb... (Engine s/n: 0F769374)... I noticed after a couple weekends ago that after cruising around for more than a few minutes, sometimes when I would come back down to idle to go through a no-wake, the engine would start to struggle a little, and sometime even stall out.. It was not every time, it seemed a bit random, but I did notice, it would only happen after a longer cruise at higher RPMs...

I also noticed that if it did stall, it was more difficult to start than usual... I would have to give it some throttle to get started again, and when it did start, it seemed like there was a puff of smoke out the exhaust, which leads me to believe the engine was extremely rich...

I haven't done any investigation yet since I got back, but I'm looking for anyones input on what might be causing this issue before I spend a bunch of time... I'm hoping its something obvious to someone, that I'm not thinking of...

My initial thoughts are:
-Check water seperator for water in fuel
-Check electric choke operation
-Hopefully last resort - check float adjustment

Just to clarify, it starts great when cold, and runs great when cruising...
I'm thinking its not the idle screw adjustments since its not a consistent problem.

Thanks for any advice

 

[AShipShow]

Anyone... Anyone... Bueler???

 

[Baylinerchuck]

Wish I could help more other than saying I can’t imagine it would be a water separator issue considering it’s intermittent. Are there any hesitations through the throttle range?

 

[AShipShow]

Wish I could help more other than saying I can’t imagine it would be a water separator issue considering it’s intermittent. Are there any hesitations through the throttle range?

I agree with you, its just one of those things that is usually the first thing someone mentions, so I figured I'd get it out of the way.

No hesitations once out of the idle speed range...

To me, it just seems like its flooding out at idle, but not all the time... I have adjusted my idle mixture screw to what seems to me like it was running the best, but maybe its just too rich, and thats why it runs okay when cold...

 

[Baylinerchuck]

Like you said, it must be something in the idle circuit. I’m not sure how many turns out from seated that mixture screw should be as base, but I assume there must be a spec for that somewhere. I would think that the float height would impact all throttle ranges, not just idle.

 

[AShipShow]

For my carb, Its 1 1/4 turns... Thats where I started when I did my carb rebuild, but I've adjusted since then... Maybe I ought to set it back to that and see if the problem goes away... Thinking of taking her out this Sunday so I'll take my screwdrivers with me..

Have you ever tried tuning with a vacuum gauge? Was thinking of trying that, but I don't think theres a vacuum port on the carb anywhere.