Same Piston - Twice Holed

[billy3rdson]

Hi This is the 1st time I've posted Ihave fully restored a 67 cb77 and it ran great until a 4 hr high speed road trip. I was almost home when the motor failed-blue smoke came out of one pipe. Recently I took the motor head off and discovered 1 piston has a hole burned through the center. I checked the parts box that I got with the bike and found a set of pistons with a hole burned in one also. What is causing this? help Please Billy

[kustommusic]

Billy, Welcome to our forum. Sorry you have to start out like this! Two things come to mind on your "holed out" piston, your timing could be set too far advanced,or you have a lean carb adjustment on the side that burned. First thing to do is get a repair manual if you don't already have one,so you can replace the piston. Second look in the VJMC link for Ed Moores tuning instructions for when you get it put back together. Third,let us know how your coming with it ! Good Luck,Kustommusic

[billy3rdson]

Thanks for the info! I am trying to locate a piston set that is .25 over stock. Any idea where I can find a set? I see plenty of .75 over and s12 kits but the cylinders were bored .25 over just before I got it and they look fine. I am sure the timing was spot on and I overhauled the carbs and blew them out with compressed air. I am going to try a different carb on the problem side and I may have had an air leak on the carb spacer block motor side o-ring.I am als going to try the next hotter plug range. Billy

[kustommusic]

Billy, Sounds like your all over this thing! Check with; EMO@KTC.com
for parts . Kustommusic

[davomoto]

Billy, be sure to check the timing at full advance, with a timing light. I believe 3500 rpm is full advance. I'd go for a colder plug, not a hotter one.

davomoto

[billy3rdson]

Thanks a million! Billy

[Peter.E]

Try classichondarestoration.com This guy is having pistons manufactured for the CB77.

Peter E.