Occasional Backfire during acceleration

pangolin

Petty Officer 3rd Class
Joined
Aug 20, 2016
Messages
91
1999 Volvo Penta 4.3L GL

Some history: I just bought this boat recently. The previous owner only used it up in higher altitude so the carb was adjusted for that. So prior to my test drive he had a local shop re-jet the carb for sea level use, where we are.

Problem: The boat is backfiring when I hit the gas hard. Not every time and it seemed to go away after running for about 10 minutes. (I am hoping to take it out next weekend to test that theory about warming up). It is just one backfire and doesn't seem to effect performance at all, it takes off and gets up on a plane just fine. Does not backfire when cruising or idling, only during the initial acceleration, and once again not every time.

where do I start? timing, carb, ? could the mechanic have screwed up during the re-jetting process and the mix is wrong?

Thanks
 

pangolin

Petty Officer 3rd Class
Joined
Aug 20, 2016
Messages
91
No Title

Thanks for that. Looks like a promising start. I found some related info(attached screenshot)
 

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Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
Joined
Jul 23, 2011
Messages
47,296
Check the usual suspects
Check plug color to see if motor is running lean
Check fuel pressure feeding carb
Check dizzy cap and rotor for corrosion
 
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