Maintenance & Technical > KX500 Original

Engine Knock

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Pmcg:
Finally got to put some hours on the new motor and have noticed a pretty loud knock when warm.  I had Todd redo the top end to run premium pump gas but am wondering if the compression is a bit too high.  Engine details are:

88mm bore
wossner windowed piston
lectron carb set a bit rich if anything
Vforce II reeds
Fatty exhaust
Power Dynamo ignition set at .86 BTDC


I can source some race gas locally but don't want to have to do it all the time.  Any thing else I should check?

Thanks

Foxx4Beaver:
is it actually pinging?....or is it more like a KIPS rattle?

I would definitely try a 50/50 mix of pump gas and C-12 if you believe it's pinging.
Todd did mine as well...and he figured 25% C-12 to 75% pump would be ok for mine...but I actually ended up going 75% C-12 to 25% pump, cause I was getting a decent amount of pinging as well.

Pmcg:
It's a pronounced knock. Not the Kips. At first I thought my helmet strap was unfastened and slapping on the helmet. What is c12?  Where can I get it? 

Thanks.

umberto:
It comes from VP Drag Racing Fuels.  You can go to this website and they have a dealer locator.

http://www.vpracingfuels.com/vp-drag-racing

sandblaster:
Doah no.... Sounds like a crank rod... When you had the top end off, did you measure the side play in the crank?

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