Originally posted by dino.tw
The STS carburettor is made of composite plastic. It will not have overheat problem. Besides, STS's spray bar(mid-needle) has 4 holes on it. Racers can lean it to get extra-power and fuel supply still will not cut off. So it don't have adjusting limit.
Check those broken crankpin,first you will find that it's sign of overheated. Because the pin area is darker and also sign of too lean. That means the lubrication is not enough. And if you measure crankpin you will find it is not round any more. It's oval. The stock crankpin is 4.29mm diameter,just measure the top-bottom and left-right places. When the crankpin has very big play,the conrod will hit the crankcase and pull apart the crankpin.
There is a case I just deal with.Yeah~ Fisher's D3 broken crankpin too. From I studied his crankpin,it is 3.94mm diameter from top to bottom and 4.08mm diameter left to right.(New one is 4.29mm diameter)So 4.29-3.94=0.35mm . That is not only a little play.
Still not ready. Verytight still I can feel what you described sparksy. I went ahead and popped the top and side to look at the progress. The Rod is still very tight to the pin don't know how you assembled it... but didn't try forcing it off the crankpin. Everything still looks beautiful inside my D3? hmmmm.
An observation that I have made during run in is that the motor does not like to run rich. It will die quickly if I have it too rich, tried differant plugs but all the same. Low speed is ok rich but High speed doesn't like fuel. Going to wait a couple days for my new 16/19T Side belts before running more (eating rear tires).