Backfires through Carb

[nntravel1]

Hi all,
I have a '04 9.9 Johnson 4 Stroke (Suzuki) with just over 10 hours on it. I had the 10 hour Maintenance done and had the dealer check a miss at WOT that had just developed and caused me to take the motor in Mid December. I get the motor back and in late January, 10 hour done and carb cleaned I had not used it until this weekend now I have an engine that runs fine at low speed but when I go to WOT it misses and backfires through the carb. Backfiring usually is timing related or valve trane, any other ideas?

 

[Dhadley]

Re: Backfires through Carb

I think you pretty much nailed it. Unfortunately.

 

[iwombat]

Re: Backfires through Carb

Backfiring through the carb can also be caused by a lean condition. If your main jets are gunky that's a possible cause. You'd me more likely to experience the backfiring on hard acceleration than sustained WOT though if that were the case.

Look to timing, then valves, and then carbs for a 4-stroke backfire.

 

[perkdp]

Re: Backfires through Carb

I'm not familiar with 4 stroke outboards at all. But thinking of 4 stroke in general, if the crank to valve timing were off, it would backfire even at low speed. right ? how about the spark advance, what if it is advancing far enough to be firing during the intake stroke ? or, what if the plug wires were crossed ?

 

[nntravel1]

Re: Backfires through Carb

All,
I took it to the dealer today I'll keep you updated about Ed's Marine Superstore in Ashland VA.

 

[Texasmark]

Re: Backfires through Carb

At 10 hrs you wouldn't expect things to be worn out. Forget that.

To get backfiring thru the intake you have to have an intake valve open when the explosion in the cylinder occurs.

You said low speed is ok and it happens at high speed only. Engines have spark advance mechanisms.

I like your idea about the timing being off.

My 2c

Mark

 

[perkdp]

Re: Backfires through Carb

wouldn't expect it at 10 hrs,,, but could have a chip on the valve face.
or sticking open due to carbon build up or something. but that usually shows up worse at low speed.

let us know what the dealer/service hits you with.

 

[nntravel1]

Re: Backfires through Carb

And the winner is Iwombat. I never would have thought a lean carb would have caused the problem but that is what I am told. $150.00 for diagnosis and repair of a carb that was fixed by Norfolk Marine during a 10 hour maintenance, so fixed it didn't run and I refused to take it back to them.....money well spent.