I installed a new carb on this 125 - I believe the old one had clogged fuel jets. The new one fired right up and has good power immediately - but the backfiring issue is still there. I was messing with it in the dark and noticed after only a minute of running it is blowing a flame out the exhaust. After a few more minutes the base of the muffler started to glow a nice shade of red. At shut off it backfired through the carb.
This is after pulling the head and cleaning a massive amount carbon. The head and piston top were cleaned and the head machined flat. The original headgasket does not appear to have been blown.
This is after pulling the head and cleaning a massive amount carbon. The head and piston top were cleaned and the head machined flat. The original headgasket does not appear to have been blown.