1989 merc 3.0 stumbles- anti syphon?

[Beachrights]

At just above idle 1000-2000 rpm it misses stalls and shakes.
I have -changed all fuel filters, water filter, plugs, wires, accelerator pump and cleaned carb as best as I could. Put multiple carb cleaners, seafoam into tank and carb to no avail.
I can get the timing to have it run good at idle but when you try to throttle it bogs and dies. I can also get the timing and mixture somewhat right to make it run crappy at best but I am getting pinging at high rpm so that will not work! I can not find a happy medium.
Would the anti-syphon [spelling?] valve be causing this? It runs fine at 1/2 throttle and WOT. Ithink I am looking at a fuel or air problem but I can not find the issue and I am tired of spending money only to find I have the same problem.

 

[Don S]

Re: 1989 merc 3.0 stumbles- anti syphon?

If it runs ok at idle, 1/2 throttle, and WOT, then you don't have a fuel problem or antisiphon valve problem, you have a carb problem, even though you "cleaned carb as best as I could." it must not have been good enough.
It needs pulled apart, soaked in carb cleaner, and all the passages blowed out with compressed air. Then put back together with a new carb kit and gaskets (you can not reuse gaskets and expect it to work).

 

[Coors]

Re: 1989 merc 3.0 stumbles- anti syphon?

And then put your timing back to where it belongs.