He states it doesn't have any restrictions on it. It would be easy to tell if there is a throttle limiter on the GG's engine just by looking at the throttle cable at the carb, or peering into the back of the carb to watch the slide open.
My thought is to check the airbox on the GG. Is it restricting airflow some way when compared to the the YZ box? I would have said the silencer but you changed that. My experience with WR250's is that the stock silencer cuts down on top end power. That got me thinking what else is cutting off airflow. I'd try running it without it's seat and/or comparing the jet size between your '06 Yamaha and the GG.
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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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