[Hollerdog]

Took the heads off to decarbonize them and to my shock i find this, it is 10 over and smooth to the touch no nail grabbing high spots, other side is fine just wondering what cuased this and whats the final verdict, i know about the oil pressure problems just haven't had a chance to check that since i wanted to do the heads first for compression test than a oil pressure after that, ran fine before except for rpm,s didnt seem right, so i changed the points, condenser, coil, plugs and wires and rectifier, i started it up and seem to run smoothly until i put the back of my hand up to the exhuast to feel for any thumping and man as soon as i did that it backfired like a civil war cannon and burnt the back of my hand, so am sure i didnt set the points at tdc or something. am about ready to adjust the vavles and put it all back together but just wondering about that spot there.
Thanks

 

[T-Mo]

Since your post in the introduction section was titled 77/400, I'm guessing this is off a 400? I moved it to the proper forum, which is the Hydrostatic Drive section.

 

[5540jd]

Looks like from fuel laying in cylinder. Backfire is probably when it pushed extra fuel into muffler and then finally lit. Check needle and seat in carburetor since electric fuel pump can push past with bad needle. Check float as well. Hopefully someone hasn’t changed fuel pump and got one too large for carburetor to handle. Good luck

 

[TempletonJDguy]

To me it looks like a rust spot from condensation/sitting. I’ve seen this before. If you have good compression and no blow by then it’s not that bad.

 

[TiredDeere210]

Looks like water to me. I say run it!