RC51 woes

[Fast4fun]

I replaced my exhaust with a Jardine 2-1 and pcIIIr. The bike seemed to run well for the day I took it out of storage before the changes. After... it backfires and dies regularly. I took it in for a custom map just to find out that the front cylinder is low on compression. The mechanic believes it is probably a valve that needs adjustment. No surprise, I am over the suggested mileage limit for a full tune-up. I raced regularly last season without any problems. Just trying to make mild improvements for this season. Does anyone have enough experience with the RC to diagnose!? the problem. I am quickly getting into a financial windfall. If it is just a valve adjustment then I'm OK. If it's more...? I guess no one said racing would be cheap. But it sure is fun!

[tzracer]

Do a leak test to see if/where the cylinder is leaking (do this after checking/adjusting valves). I have not had any problems with my RC, but I only have about 2000 miles on it.

[tcchin]

Adjust the valves and do a leak-down test. Also, make sure the PC3r is properly grounded. For grins, remove the PC from the system and see if your stalling/backfiring is affected.

[unforgivenracing]

You said it your self that its do for a full service.  DO it.  while your getting the valves serviced, have them do a leak-down on the head when their done.  I dought its major.
Did you check to make sure the header bolts are still tight?

[timsotherrc51]

Had the valves checked... they're ok. Still not holding pressure in the front cylinder. Must consider whether or not to invest the dime to rebuild. Suggestions are welcome.

[wilbur]

Give it to me for free.

Seriously it can only be piston rings or valves. Pull the head and you'll know for sure.  But before you do that, a quick way to check rings is to squirt some oil in the spark plug hole and do a compression check.  If compression is up after squirting oil in the cylinder than it is a ring problem.  If compression dosen't change it is a valve problem.

[Fast4fun]

Pulled the engine. There is some scoring of the cylinder. Having it bored 1/4 over with genuine honda pistons and new rings. Since I have it in pieces, I am looking for engine modification suggestions (Cams, porting, etc). See related thread. I will post the results. Even with the loss in compression It was pulling 117 hp on one dyno.