Originally posted by the Eel
just bought the bike used so I'm not sure when the last top end was, though I have put close to 40 hours on the bike already since I bought it. Does that mean it's time ? It seems to run well but I still have that low end gurgle.
That's a lot of time on a 125 (& U don't know how long the prev. owner had on it), tho perhaps not 4 a euro bike as they use forged pistons; it's certainly time to pull it & measure everything, definitely replace the rings & clean the exhaust valve - both of the latter can be detrimental to your low & top-end performance demands & produce odd & counter-intuitive jetting symptoms that send U in the wrong direction.
To get you thru the SoCa riding season, which has just started, I recommend we do the above now (with a stock piston in-hand just in case) & later when U can spare the time sending the jug to Eric for mo-everywhere porting.
I do not know if an aftermarket pipe is better than the stocker. expensive, but worth a try if others concurr, but not necessary.
Takes ~1 hour to pull the top end apart; 2 to put it back together right, torque specs., gaskets, & all. I'll be in Burbank from 9-11 this Sat. if U want to meet up your way & get it done, or do it in my garage Sat. afternoon.
I have all of the tools escept for a ball hone; if U can tell me the cylinder dia. - look in the manual - I'll get one (as Eric recommends) to clean things up.
Do get a piston kit, wrist pin, bearing, clips; head & base gasket; intake gasket if the carb intake track attaches to the cylinder (not needed if it is a case reed intake). Should run ~$100-150. Perhaps Eric's in Pasadena has the parts in stock.