Old rc magazine's

[buzzkill]

Or was quite responsive for being such a small engine. I actually never thought about Yamahas exhaust valve in dirt bikes.

In the late 80's they started doing the power valves, very fast light bike great canyon burner
https://www.yamahapart.com/yamahapowervalvesystemypvs

 

[Blown67Sedan]

I have boxes of old RC Car Action and various RC car magazines, going back to the mid 80's or so.
One has the Clodbuster on the front and a full review back when it first came out. Yes, I'm an old dude. Lol.