stalling at idle

Started having an issue this morning with my 76 SN. Dropped it in this morning for the first time this season. Started fine, took it up to speed for a couple laps around the lake, and brought it back to the dock to use later. Went to go for a ski an hour later and I couldn,t get the boat to idle below 1100-1200 rpm. It idles high when cold and I gradually bring the rpms down as it reaches temp and the auto choke opens, but now it just cuts out and stalls/shuts off when I try to get it to idle normally. Then I cant get it to start until it sits for a while, almost like its flooded. If I go to start it 45-50 minutes later, it starts right up, but again, it wont idle. It just shuts off when I bring the throttle back to idle.


I have maybe 7-8 hours on a freshly rebuilt Holley carb going back to last season- this was my first time in the water this season. Could my issue be as simple as the old gas, even though it was stabilized for winterization? A mechanic friend of mine explained to me that I may have a stuck float, which can cause the engine to act like its flooding, or some kind of blockage or vacuum leak in the low idle circuit. Suggestions?

You said the electric choke does open up ok?

Not sayin the gasket is your issue but it sounds exactly like one I worked on some years back.   Carb had been rebuilt and automotive gaskets used under carb and adapter plate. Ran ok for short time and then wouldn’t idle below 12-1500 rpm and was hard to start. After some head scratching, finally found, side of gasket under adapter plate was sucked inward, leaving a gap, because there wasnt enough material to clamp it solidly between adapter and manifold.   Unless you make gasket yourself, you’ll have to get from PCM supplier like SkiDim, Nautique Parts or local CC dealer. Automotive types aren’t quite wide enough.

You could try carefully spraying your starting fluid around the carb/adapter base while it’s running and see if this affects idle. Unlit propane torch open fully might work too.   You just want to temporarily enrich the lean condition.    If doesn’t make a difference then may not be the problem.

What he means is not wide enough on the flat.

About a year ago you had a stalling problem and replaced both gaskets and cured your problem..

The bottom one is the one that can easily give issues if it was replaced with one that wasn't wide enough even if it was just replaced last year and worked well at that time.

The PCM gaskets are wide and also pretty thick which helps too.

Like Mac said, PCM gasket or cut your own for the spacer to manifold joint.

Here is what the underside of that spacer looks like,this is the vacuun source for the PCV on the valve cover-



This is the gap that caused by using a standard 4 bbl gasket,you can move it a little so that it looks like it closes the gap but being under high vacuum will leak soon.



This is a PCM gasket,you can see how much larger it is. So far I have not found a readily available aftermarket gasket that fits.

.