Well, I've estimated I've got over 100 hours on this topend and it's time to replace it. Probably close to 2/3 of these hours are woods riding, the other third mx. I'm a novice racer (not a "screamer", and I love the low and mid of this bike!). This will be the 2nd piston (Wiseco) I've put in the bike since new (I generally do a piston a year -- approx 75 hours) and the first time I've cleaned the powervalve. The first 50-70 hours on this last piston I was running pretty rich. I've jetted and reached zero spooge, near perfect plug chop, smokes only on first start of the day, and instantaneous throttle response. My settings: 155, 2nd from top, 45 pilot, Castor 927 with 93 octane pump gas (32:1), PC pipe and stock silencer (I've got the PC shorty, but I think the stock pipe is a tad quieter with virtually nil performance difference) and a BR7ES in sunny Florida at sea level. I probably don't clean my filter as often as I should (every 10-15 hours), especially in the conditions that I ride (very sandy). I've not done any type of modifications to the cylinder or replated and feel like I'll probably never need to (although I may purchase DFII when this set of reeds go bad (only had to replace the reeds once since I bought the bike).
The piston looks nearly perfect (compared to the pic Eric has posted on his site). Although there is a tad (1/4 inch by 1/4 inch) bit of blow by below each ring on the left side of the piston. Either my rings are showing their age or the cylinder is a bit "out of round." Other than that, no scoring of the piston or cylinder.
The flapper portion of the powervalve and the exhaust port had a bit of carbon build up that cleaned up quickly with a bit of scraping. The exhaust valves, idle gear, and main valve chamber were FULL of crud! Black, greasy, sticky, chunky, goop -- that took 3 hours to clean! I don't know if it's because I've never cleaned this before or if it's a product of the castor oil. Although, my powervalve still operated smooth as butter, no broken pieces and cleaned up nicely!
I'll attempt to include a couple of pics too, just for a visual if anyone cares to see. This is the second time I've tried to post this (this first time I hit "post" and it told me my picture was too big and deleted EVERYTHING I had typed! This time I'll save it first!).
Oh yeah, I almost forgot, I ran a compression test at about the 50 hour mark and showed about 230 psi, then ran another one about 15 hours back (near the 100 mark) and had 170psi. Manual says between 115-178 psi is usable.
The piston looks nearly perfect (compared to the pic Eric has posted on his site). Although there is a tad (1/4 inch by 1/4 inch) bit of blow by below each ring on the left side of the piston. Either my rings are showing their age or the cylinder is a bit "out of round." Other than that, no scoring of the piston or cylinder.
The flapper portion of the powervalve and the exhaust port had a bit of carbon build up that cleaned up quickly with a bit of scraping. The exhaust valves, idle gear, and main valve chamber were FULL of crud! Black, greasy, sticky, chunky, goop -- that took 3 hours to clean! I don't know if it's because I've never cleaned this before or if it's a product of the castor oil. Although, my powervalve still operated smooth as butter, no broken pieces and cleaned up nicely!
I'll attempt to include a couple of pics too, just for a visual if anyone cares to see. This is the second time I've tried to post this (this first time I hit "post" and it told me my picture was too big and deleted EVERYTHING I had typed! This time I'll save it first!).
Oh yeah, I almost forgot, I ran a compression test at about the 50 hour mark and showed about 230 psi, then ran another one about 15 hours back (near the 100 mark) and had 170psi. Manual says between 115-178 psi is usable.
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