Yamaha 9.9 Backfiring Problem

[carboman]

Starts fine, idles fine and runs fine at higher rpms. However, when ramping it up to speed, either half or full, it is backfiring out of the air intake area of the carb.

I have installed a carb rebuild kit, new choke valve and main jet and new diaphram in the carb. It seems better but still back fires. Any help is greatly appreciated.

Dave

 

[rodbolt]

Re: Yamaha 9.9 Backfiring Problem

3 main reasons for backfire from the carb.
lean intake charge,overly advanced ign timing or leaking intake valve.
myself I would start with checking fuel delivery into the intake manifold.
if it only backfires on acceleration pay close attention to the accelerator pump circuits in the carb.