I recently did a top end and used the wiseco 13.5-1 piston. The bike cannot be started by a human being. We finaly got it started by towing it behind a truck in gear while kickstarting it. It ran like a champ until it was warm and then I turned it off to cool down. Then I tried to start it up again.. no dice. So I thought about the research I did on the hi compression piston and I figured no one would condone such a mod if it was imposible to start like this. The kick locks up with compression and takes a bit of standing on the kick start to get through it. So I came to the conclusion that something was arye. So I I checked the valve clearences and all of them were in spec but the lifter under the decompression nipple (wich I belive is why it wont kick over) there is excessive gap. .508mm I didnt test the clearences before I tore the bike apart but my friend says it was a tad noisy. Im not sure why I didnt have a similar problem with this before. I suppose the hi comp piston exagerates this. I do know that the valve isnt stuck open because the bike has amazing compression. So do I just get a new shim and go with that and be good? So if I have .508 clearence and there is a 175 pad in there Should use a 205 pad? Oh yeah and this is on an 04 450F Also is it true the crf450 shims will fit this bike? Thank you a bunch guys.. Im so close to getting this thing working again.