Bogs and stumbles

"Thanks in advance to all who

"Thanks in advance to all who respond. "89" 4.3ltr. Merc, 2bbl Rochester, Thunderbolt ign. Engine has 1000 hours, and has been well maintained. I've put 200 of these hours on it and it has always had this problem. Motor starts,idles, and cruises flawlessly, but when I punch the throttle to wide open it runs poorly and never corrects itself until you slow back down to cruising speed. After reading previous posts here's what I've done, had carb rebuilt, R&R plugs,wires,cap,rotor. Confirmed clean screen in tank, anti-syphon valve is operable, choke works properly, replaced all fuel lines thinking maybee that the old oned were collapsing, installed a fuel water seperator, checked in carb fuel screen.Here's what I haven't done, coil, fuel pump, pick-up in distributor, checked timing. Any suggestions would be greatly appreciated. Safe boating. GPS"

"GPS:

Check and reset timin

"GPS:

Check and reset timing per engine specs. It may be slightly off the spec.

If the carb has an adjustable accellerator pump; look for three small holes in a row on the pump lever; change the position of the pump rod to the lowest position (I THINK; GUYS CORRECT ME IF I AM WRONG) so it will draw a larger burst of fuel in order to accellerate.

Test the fuel pump output or just replace it if it is original for peice of mind, safty's sake and future failure.

Will it run at WOT if you slowly accellerate to the WOT? If it does so, then I might rule out the ignition control module and coil. But, remove the dist. cap and see if there is rust on the optic trigger sensor (pick up). If yes, replace it. My 87 4.3L was giving me fits until I did that.
Recheck the timing after changing any dist. ignition component.

Guy"

Sounds like the usual problem

Sounds like the usual problem of too small an accelerator pump shot. Try moving the linkage on the arm to provide a greater shot. There's usually multiple holes. Use the hole that moves the arm the most as the throttle opens.

Jeff