First: Don't buy Champion Plugs
 

We pulled the starboard plugs first and had 2 big OH-NO's. # 7 cylinder central electode cracked and missing as well as part of pocelain insulator. Same on # 2 cylinder. NO COMPRESSION on # 7. POS Champion plugs can't last 40 hours. Smell of gas in oil. several plugs were loose.

Port engine- Plugs all look normal- all tight.

We gapped 16 new AC MR43T to 0.40" and installed.

I have to call Tyler Crockett to talk about fixing the bum engine.

Wannabe

If the plugs came loose, that could be the reason the electrodes cracked, and could damage a valve.

The gas in oil, could be from running with the bad plugs, not burning the gas, and washing down into the crankcase.

Might just have to replace the valve(s) in the #7 cylinder, and install new plugs tight, and could be ok.

I know myself, I have installed the plugs all finger tight, and forgot to torque them down, resulting in loose plugs and cracked electrodes.

I hope it's the valves and not a cracked piston. I agree the gas smell is from the cylinder being washed down.

The original backfiring was through the intake- not the exhaust.

It's like 2 different people rebuilt the 2 engines. Dufus did the starboard engine and Dinkus did the Port engine.

Either way the Champion plugs stink. They were the Non- marine kind.

Wannabe

Throw all the Champion spark plugs into the water and only use the ones that float.

I agree !!!!

Wannabe

Detonation will sometimes cause the plugs to loosen. It will also cause the insulators to break. I'd check that out carefully

Patriyacht- I am aware of the possible detonation issue- thanks.

The engines were over advanced a couple of degrees. The plugs on the Port engine look good.

Wannabe

Keeping my fingers crossed it's only a bad valve. Good luck.