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Mercarb off idle stumble problem

T

totomax1

New member
"Great Forum-responses are top

"Great Forum-responses are top notch! I have a challenge for the experts.

98 Regal 4.3 Alpha 1 with a 2 bbl Mercarb that has an annoying major off-idle stumble/stall and to a lesser degree poor idle quality/run-on that is driving me to drink. Does not seem to make a bit of difference if cold or hot. Slightest bit of throttle and it will stall unless you really finesse the throttle. No backfire associated with stumble. It runs phenomenal above 1500 RPM. Have rebuilt the carb,reset float level (numerous times), checked accelerator pump output and tried various pump stroke settings, checked choke operation, drained/refill with fresh gas/Seafoam, checked electric fuel pump pressure (6-7 psi) (even did the mercruiser service bulletin pump check valve test), checked timing. Replaced: float,idle mixture screw, coil, plug wires, distributor pickup, water separator filter and carb filter.

I am stuck on the fact that it has to be a carb rich idle condition because it does not backfire. Have not done: cap/rotor,plugs, checked spark advance, or compression check simply because it runs so awesome above 1500 RPM. What could I be missing? I am really starting to not like Mercarbs. Any ideas, opinions,input, would be greatly appreciated."
 
"Pull the spark plugs and chec

"Pull the spark plugs and check the burn color. White to light tan is too lean, tan to brown is very good, darker to black is too rich. Dirty plugs won't spark well at low RPMs. Enrich the mixture 1/4 turn and see what happens."
 
"Sure sounds like accelerator

"Sure sounds like accelerator pump issue.
Are you sure your float level is set high enough?
If all else fails, you may want to bite the bullet and get a rebuilt carb.
Rod"
 
"Couldn't help but notice

"Couldn't help but notice you didn't mention changing spark plugs. Worn plugs could cause this
to a degree, as a worn plug usually has an enlarged gap.
Kurt

"summers on, get it on!""
 
"Not going to add much value h

"Not going to add much value here, but I've seen and owned too many Merc 2brl boats that had the same "lean transient throttle condition"... at least i've always assumed it was a lean condition... perhaps associated with accelerator pump volume or something. Yours sounds bad."
 
Appreciate all the timely inpu

Appreciate all the timely input. I will pull the plugs and try to get a read on them to determine if I am dealing with a rich or lean condition. I have a tendency to apply an automotive mentality to marine engine driveability problem and I am not sure that is a good thing ! As a last resort I have a lead on another mercarb to try. In any event I will keep the forum posted.
 
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