Engine Backfire
 

I have a 96 velocity 26 with a 454 magnum 415hp mercury engine. Bravo 1 out drive. The boat has been in storage for almost a year with a 1/4 tank of gas in it plus a 1/2 of fresh gas. Wed night i took the boat out and it wouldn't't clear out over 3400 rpm would only do about 40 mph. Saturday I changed with plugs and the fuel filter. That night it ran great, cleared out would do about 67 and run high rpm, but by the end of the night it was back to running bad again. This Sunday I tried to use it again but kept popping, wouldn't't clear out or run over 4200 rpm. I was going to drain the rest of the fuel in the tank out but I pulled the gauge sensor out i didn't see any water in the lowest portion of the tank. Ran the rest of the gas out of the boat, filled it up with fresh 93 octane. and it still won't clear out, except if it's not under load. when in gear it eventually will get up to 4200 rpm spitting , sputtering, and popping. My question is , is this a carb problem or timing? Has anyone had trouble like this before , and might know what it is? thanks for your time. Joel H.

Re: Engine Backfire
 

Sounds like a "lean" pop to me. May be something stuck in the secondaries of the carbureator or a bad fuel pump.. That's kind what is sounds like to me without being in the boat and hearing it for myself.

Re: Engine Backfire
 

I'd check timing first. At least, try to turn the distributor without loosen up the bolt. If it moves, it's probably your answer. If it does not move, check cap and rotor. If ok, check your timing to make sure it's ok. If evrything is ok, then I would doubt the carb. By the way, are 100% sure spark plug wires are not taking humidity ?

Good luck.

Re: Engine Backfire
 

I a, with jeff, would also think it could be a problem with timing, You have already knocked out other possible problems. I would check to see if the dist is tight, put a light on it.

Re: Engine Backfire
 

The wires are newer MSD 8mm's, and look to be in good shape. Thanks for the advice but my next question is What degree advance should the timing be at ?Thanks Joel H.

Re: Engine Backfire
 

Did you replace the fuel filter again - ie: after removing all the fuel ? If not I would since this may have made it run better the first time.

Re: Engine Backfire
 

When the motor pops, does it pop back thru the carbureator or the exhaust?

In my experience to get a "pop" you would either have the ignition wires arcing, not enough fuel, too much fuel, bad plugs or a bad iginition module.

Depending on the size of prop 3500 is probably right about when the secondaries open. :rolleyes:

Re: Engine Backfire
 

both through the carb and the the exhaust. I'm about to check the timing this afternoon but i'm not sure on the degree of advance it should have, anyone know it's the 454 415 hp merc

Re: Engine Backfire
 

Is it the stock motor that came in the boat or aftermarket. i knowalot of the merc's say it right on the tag thast on the valve cover..

Re: Engine Backfire
 

If It Has The T-bolt Iv It Is 10* Initial And 24* Advance 34* Total.