Yz125j bored out to 250cc

[Ted]

I just did some quick calculations it only needed to be bored out to about 80mm thats 24mm os no wonder it goes so well.

its bored out so much the piston is now air cooled "flapping in the breeze due to no cylinder left"

You Honda boys just can't grasp BRUTAL Yamaha power. All Yammy 125's are waaaaaaay more powerful than the competitions 250's. face the facts and move on

[kdx Geoff]

That air cooled piston thing got me thinking about the low friction environment due to minimizing cylinder wall contact that this visionary has perfected, or could this be some secret works bike exposed ?

[OverTheHill]

my 'briggs' lawn mower motor has an 'alloy bore' [so i discovered]. OH GOD!! maybe he's having the last laugh 'on us' & just kept boring it till it fitted. Damn. Probably used one of them yamy 250 pistons on ebay that suits 'both' yz250 & 360--maybe not.

[TonkaF1]

I still reckon the classic part is the wind deflector on the front guard. It was either running way too cold or it is an attempt to keep the front wheel down.