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43 possible fuel or carb problem

J

jg106

New member
1989 4.3 mercruiser idles and

1989 4.3 mercruiser idles and revs good but after its in the water for about 5 minutes it.loses power and backfires out the carb after it does this it will only move by giving it as little throttle as possible then it will gradually let me throttle about halfway up then do it lose power again have replaced fuel filter and have ran about 3/4 of a tank of fuel through it from a different gas station. I am in the process of draining and cleaning the tank checking plugs and replacing filter again. Am I on the right track?
 
"First check timing...it may b

"First check timing...it may be way too far advanced. Then turn your mixture screw(s) on the carb out by 1/4 turn to enrich the mixture a little bit. In fact, it might be better to find the specs for your carb, and completely reset the mixture screw(s) to their baseline settings."
 
My 4.3 did the same thing. Onl

My 4.3 did the same thing. Only able to feather the throttle or it would backfire thru carb. Found out the accelorator pump/plunger in the carb was warped from todays gas and additives. Part cost $4.00. The way to check for this is to disconnect the cable at the carb (engine off) and look at the stream of gas it pumps down the carb throat. If the stream is not steady change the acc pump plunger.
 
"that's the infamous lean

"that's the infamous lean pop.

Accel pump very likely to be part of the problem. Other "soft' parts probably need replacing too.

While you're cleaning the tank, check the pickup tube and the anti-syphon valve for restrictions, too. The last item to check is the fuel pump. A fuel pressure reading should help there."
 
"accell pump seems to be worki

"accell pump seems to be working fine, havent got to the plugs and wires yet, are they even a possibility since it idles and revs good?"
 
It is not getting enough fuel

It is not getting enough fuel above idle. If the accell. pump is OK then perhaps the fuel pump may be failing. Have you ever changed the fuel pump housing filter?
 
"drained fuel tank added some

"drained fuel tank added some fresh fuel, replaced inline fuel filter, cleaned screen filter where fuel line goes into carb, sprayed carb cleaner in carb in ever hole i could find and cleaned flame arrestor, went for a test run and ran perfect, dont know which thing did it but it runs good for now...thanks for the advice!"
 
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