470 Mercruiser Backfires out of Carburetor?

Question

I have had this problem off and on all summer. The Engine seems to be running fine. The boat is used primarily for water skiing, so performance out of the hole is very important. When pulling a water skier, I need to give the boat full throttle on take off out of the hole. The engine between 1200 to 2000 rpms will backfire out of the carb. Once with starts, the engine does not get past this rpm range and sometimes stalls out. If we start slowly bringing the rpms up to 2000, then apply full throttle, the engine operates normally. The engine cannot respond normally with a full thottle start from 1000 rpms without this backfire.

Is this a carb issue?

Also, is there any adjustments I could make on the carb / accelerator pump?

Thanks

Answer 1

While it might be carb related, I'd look at timing and or sticking valve. At low rpm, with high loading, you might have a sticking valve that would cause backfire through the carb, which is dumping the max fuel into the manifold at the same time.  Is this an older engine. If so, I'd take it to a mechanic who can do a dyno test, that should answer any questions.  Good luck!!!!

Answer 2

Take it to your Dealer.  The Explosion potential could KILL you.

Answer 3

Backfire through the carb is always due to rich mixture.

Check your spark advance linkage.

Answer 4

If you have a Quag=jet than that's a typical fault> Secondaries are opening to soon> Replace the vacuum pod> Check the timing> Change the fuel filter in the carb>