On my '02 300XC, I'm running a .3mm gasket AND I milled .025" off the cylinder bottom. I have not have the squish changed. Better low and no loss of top, but I do run a 50/50 mix of 112 octane race gas with premium pump.
The squish gap went from over .080" down to .052" with these mods. GG sets these engines up with a lot of clearance, but mine runs better with it tightened up to more "normal" specs. I suspect from reading everyone's posts that there might be more bottom available in having the head done, if it was a 250 I would have done this already. 50 hours on the motor since the last rebuild and still running strong. This winter it is scheduled for a teardown and I might give RB a call.
Decking the cylinder only cost me $25.
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 "Conviction is a luxury of those on the sidelines."
'13 Beta 300RR - race bike
'02 GG300XC - "Billie Baroo"
'01 DR650
'02 GG 280 Pro
'06 YZ 250
'07 WR450
'00 TT125RL
'94 YZ200 - custom keeper
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