October 31st, 2016, 12:27 AM
Joined: Nov 2001
From: Ely, England
you need to shim out the starter clutch and strengthen the spring on the sprague. then the third item is to look at the rollers in the sprague very, very carefully. if you can see 1mm wide flats on them then sprague bearing is too worn to contninue and you need a new one. best to start with the new one AND the strengthened spring from the off.
the 450/501 can get awaay with flats IF things like the two are repaired, the decomp is working etc but the 650 really, you need to stop pissing about, get the bearing, get the stronger spring and the shims.
as to WHY, it happened well, obviously the decomp is the absolute #1 reason, and the second and the third. the decomp MUST WORK simple as.
finally, as they get older, the bearings in the cover and the crankcase go. all because you kept hitting the button!!!!
I do a kit called the SRK.