carburetor backfires under load

[D. Engstrom]

I have a 1986 Sea Ray with a 140hp Mercruiser - 2 barrel carb. The carb is a Mercarb model 1389-9350. It will idle fine and run smooth at higher RPM's but when I hit the throttle from idle the motor boggs down and then backfires through the carburetor and I have to pump the throttle to smooth the engine back out. I was told I would need a carb rebuild. Any ideas?

 

[kart33]

Re: carburetor backfires under load

Backfiring typically identifies a timing problem. The spark is hitting when a valve is open and it comes out through your carb. Check the timing.

 

[petryshyn]

Re: carburetor backfires under load

Backfire from carb is commonly caused by a lean condition:<br /><br />>weak or plugged accelerator pump circuit<br />>power valve stuck in lean position<br />>transfer slots plugged<br />>manifold leak or vacuum line leak<br /><br />I'd be doing a carb overhaul. Especially if it idles and runs OK at high RPM. That suggests that there is no leaks........