1988 Mercruiser 3.0 sterndrive stalls when returning to idle

[rehgarde]

[h=2][/h] [COLOR=#6A6A6A !important]July 16th, 2016, 12:32 AM[/COLOR]



I have a 1988 Mercruiser 3.0L 181 CID 130hp sterndrive engine that is having the following issue.

Starts fine, holds a low idle at 600-650. It does sound a little rough at this level.
Shifts into forward/reverse and cruises along slowly no issues. Can leave the dock at slow speed in reverse, stop then move into forward and cruise along fine.

***When trying to throttle up, sputters and almost dies, hesitates when trying to push to full throttle, but then catches and goes along fine, up to 32-35mph. This happens if I am easing into it, but more when I am pushing forward faster to simulate pulling up a waterskier.

***AND, more troubling,, when returning back down to idle slowly, or to go into neutral, it always sputters out and stalls. The engine will start back up without an issue.
I have tried slowing down in increments, or very quickly, with the same result each time. I will slow down to a point, let it run there for a bit, but when I take the next step slower it sputters and dies. It starts up and I can slow cruise with no issues.
Little problematic when I think it is OK, then it stalls as I am reaching the dock!

Last year we had the shift controller replaced,and the accelerator pump replaced.
This year I installed all new plugs, new cap, points, condenser, and new ignition coil. Gas is end of last season but had stabilizer in it. Also timed the engine to 8, but see now it should have been 6, so I will adjust that tomorrow. Points were NOT gapped yet.

What is my next step in diagnosis/repair of this issue?
Thought carb rebuild, but would have thought when the guy replaced the accelerator pump, that would be part of it?
Thought shifter adjustment, but it goes in and out of gear fine when at low speeds (unless we just came from high speeds) I wil take it out for a slow cruise of the lake at 5-10mph, and be able to shift to neutral, reverse, etc with no issues.

If I need to rebuild carb,
is there an easier way to tell which kit I need. There seem to be two, depending on the accelerator pump. Since I didn't change it, I don't know if it is straight or 90deg. My # on the carb is 1389-9562 3.0L

Thanks for whatever help you all can give!

 

[hemi rt]

Some carbs have an idle back valve bolted to the side of the carb, when the linkage hits this valve it slows the return of the throttle plates to idle, if you have one have some one open the throttle then quickly return it to idle, the throttle linkage should quickly return to a point then slowly return the rest of the way slowly. The valve will allow the throttle to return slowly for approximately the last 3/16" of travel.

 

[Erock]

I'd set the points and timing right first. Could be getting too much fuel. If I'm not mistaken I think you can adjust the pump stroke. Just because it was rebuilt doesn't mean it's right. That's just from my own personal experience.

 

[stonyloam]

I would do two things, up the idle to 650-700 And with it idling turn the idle needle valve in the base of the carb in until the engine starts to stumble, then out until it is running smoothly and keep going until it starts to stumble again. Turn it back in to get it running smoothly again. Readjust back to 650-700 if the idle has changed. Initial setting for the idle screw is 1 1/2 turns out.