carb popping over 2500rpm

[plasmud]

Last time out the engine ran hot, coupler blew, not too hot, but hot enough for the engine to diesel for around a minute.
After coupler replacement the boat runs fine and smooth up to 2500RPM but any thing over that the carb pops like popcorn, like a backfire.
I am puzzled, what should I be looking for?

 

[Vanover]

Re: carb popping over 2500rpm

What kind of boat and motor?

 

[plasmud]

Re: carb popping over 2500rpm

sorry, its a 1990 galaxy alpha one merc with a 4.3 l engine

 

[Vanover]

Re: carb popping over 2500rpm

Sounds like a timming or maybe a vacume leak. Normally popping or backfireing out of the carb is timming realted. You didn't change that, so i would maybe check vacume. Maybe something came loose. You could check fuel. If your idle circut is high or fuel delivery is wrong you can deisel after you turn it off. You said it got hot, how hot?

 

[Vanover]

Re: carb popping over 2500rpm

Normally a motor is fully avanced around 2750-3300. If this is not happening it could stall you out. Just my thoughts though.

 

[6meter]

Re: carb popping over 2500rpm

Is it more popping than backfiring? Rapid popping? It's a coil. If it's more backfiring, you could have dizzy issues, valve situation, lean carb.

 

[John_S]

Re: carb popping over 2500rpm

Last time out the engine ran hot, coupler blew, not too hot, but hot enough for the engine to diesel for around a minute.
After coupler replacement the boat runs fine and smooth up to 2500RPM but any thing over that the carb pops like popcorn, like a backfire.
I am puzzled, what should I be looking for?

Dieseling for a minute has the likelyhood of sucking water back into the exhaust. One or more of the valves may have rusted and is/are sticking. Do a compression check and then a leakdown if there are issues. A vacuum gauge may indicate the problem, as well.

 

[LAC_STS]

Re: carb popping over 2500rpm

My engine was doing that same popping through the carb. It ended up being IGN related. Specifically the resistor wire was not cooling down or something when rpms were up. I replaced with a ballast resistor and all is well now.

So check everything ign related.

 

[nitrosteve]

Re: carb popping over 2500rpm

I had a similar issue popping through carb. Ended up being a blown head gasket between cylinders. Hope its not that but just my 2 cents.

 

[Steven D]

Re: carb popping over 2500rpm

My popping thru the carb was caused by a chipped lifter wearing the cam lobe down (exhaust on #5). Ran the same load or no load, popping came down in the RPM range as the lobe wore off.

 

[Bondo]

Re: carb popping over 2500rpm

Ayuh,... In My experince,...
Popping/ backfiring through the carb, At Higher Rpms, Under Load, is most always caused by a Lean condition....

Check the fuel system for restrictions...

 

[plasmud]

Re: carb popping over 2500rpm

I should know something tomorrow, if they found it. if not, I will try all you guys have told me myself. thanx

 

[plasmud]

Re: carb popping over 2500rpm

got the boat in the water yesterday, the dealer told me it was only popping in a very specific range and that it might be hard for me to even hear it. he said they were right down in the engine and were listening for it.
e told me he riched it up a bit and gave me a bottle of carbon out or carbon clean or something. told me to get the gas tank down to 1/4 tank put the bottle in and run it nice and fast till almost out of gas then refill the tank. he said the popping would be gone.
well, to use up some gas i took it out and now the engine wot is 4500rpm's, it used to be 4000.
I couldn't hear the popping at any range so if it was there it was not very noticeable.
Best thing is, after the coupling was replaced, the WOT is now 4500!