Backfire Thru Carb

[MitchStellin]

Let her warm up for a few minutes at idle speed, came on plane and heard a pop, opened the hatch and saw a backfire thru carb going on plane, checked the oil for cam parts, no water, metal and clean, started again, got on plane and pop. Ran for a few more minutes and went to 4000 rpm, no pop. Is this moisture in the distb? It was either that or timing, this has never happened and the boat was drenched in a downpour. Then it was covered for a few days and the terarium effect took over. I think it is ok and was just a little moisture slinging around and throwing things off. I will put the timing light on it to be sure but think it is OK. What do you think? Am I on track?

[cooltoys61]

take dist apart (cap off)or may not dry soon enough. If timing is not retarded,that is most likely it. My .02

[MitchStellin]

I was about to do that but the thunder started again so I closed her up. I think you are right, that is the next step for the next time. Thanks. Can timing go away after only a few outings? I have about 10 hours this year....and don't say "yes it can and that is a sign the cam is going away" I don't want to hear that

[cooltoys61]

Are you carbed? Could it be flooding? I had a boat do that to me once,kept loading up and backfiring even though timing was on. One carb was just leaking all the time.

[MitchStellin]

That is a good possibility, I seem to smell gas in the engine compartment when it is closed up and this engine uses more fuel, alot more fuel as found out by me when it ran out of gas 1/4 tank from the other. I may have a float that is stuck huh?

[Rambunctious]

Hey Mitch,

try swapping carbs and see if the backfires move to the other engine. might be the easiest way to trouble shoot.
you could also monitor fuel and see if that other engine now burns excessive fuel

sure hope it is not the cam.

Rob

and yes. i want the shore power cord. we'll talk

and i got a deal. I 'll trouble shoot your carb problem on the water and you replace my starboard seawater pump impeller.

[MitchStellin]

Rob, no way on the pump, I don't have 4 hands and can't stand on my head that long. I am sure the cam is OK, when my last one went it was a pop out the exhaust, this is clearly out the carb. I will run it again but think it is moisture as this was running perfect when I shut it down last time. The previous owner said he did nothing to the carbs on the rebuild so I bet they are ready for one.

[dyno]

Mitch just replace both the dist caps its cheap insurance. I do every year,since I had one go bad....

[Cord]

If you poped the carb and it didn't have power valve protection, you could have blown your power valves. This would show up as richness at idle.

Also, if it was really wet and your plug wires were questionable, you could have had a cross fire between two wires.

I'm sure that this isn't your problem, but a bad cam, springs or valve could also get a back fire out of the carb. Those items cost too much money to be your problem though.

[blue thunder]

If you have a vacuum gage take some readings. Will tell you a lot about the valve train condition.

BT