Heat pitting in firing chamber?

[Martin Brody]

Pulled the head off my J25 and found this(top cylinder). Only problem this motor ever had was some backfire/blowback(hard to describe, would happen out of nowhere on cold starts until the engine warmed up) did not stall but pops and almost stalls then levels out again. Used to do it about 5 times until the engine warmed up. Seeing as that was the only problem I though that might be the cause. I noticed the top cylinder firing chamber is a lot cleaner than the lower one. There was barely any carbon buildup in the top chamber compared to the bottom. Spark plugs look good.

I have pulled apart to make sure water channels were clear(they were) and now putting it back together with the usual(gaskets,water pump kit,carb rebuild). I am also going to grind it down a little to avoid hot spots.

What would cause this?

 

[robert graham]

Re: Heat pitting in firing chamber?

How did the spark plug look on that cylinder? Looks like a very lean and hot firing condition in that cylinder, maybe dirty carbs causing lean condition. Better to deal with this before you melt a piston. Good Luck!

 

[kbait]

Re: Heat pitting in firing chamber?

I agree w/lean condition. Possibly water intrusion due to the 'clean'. I'd do the gaskets as you said, get new plugs and run it. Then check plugs for condition/color.. should look the same.

 

[Faztbullet]

Re: Heat pitting in firing chamber?

Looks like the upper crank seal make be leaking causing you to run lean on top cylinder. This would explain your lean "pop" till it warmed up....

 

[Martin Brody]

Re: Heat pitting in firing chamber?

Thanks for the info. I will look into once put back together.