Boring 125's to 144's

No 80 over refers to 0.080" which is 2mm of overbore. (1mm=0.03937") I don't know which bike you are talking about but the formula below will allow you to calculate the new displacement. Get out you calculator rocket scientist. :scream:

Volume(cc) = {([(Bore(mm)+2.03mm)*0.5]^2)*PI*Stroke(mm)}/1000

send your cylinder to eric gorr, he's just about the only source for the piston kits and besides the cylinder will need to be plated after it is bored, you could track down the parts and have a company plate the cylinder for you but you'll have much more money time and effort than if you just do it right the first time. When I had eric do my '95 with the 144, cut for high test pump gas and ported for all across the band the bike flat out ripped, it was without a doubt the meanest 125 I've ever been on, but it still didn't perform like I had hoped so I sold it at a loss :(

Originally posted by smb_racing
but it still didn't perform like I had hoped so I sold it at a loss :(

Click to expand...

May I ask you what do you mean by that?
What did you expect,(or wanted) the bike to do? ect.?
Was 144 to much for the weight of the 125?
Would a 133 be a better choice?
Was it way too squirrelly?

I dont mean to put you in a spot. Just wondering cause I want to have
(now its my son's though) his YZ125 a couple of cc's bigger for his FMX riding.

Thanks..

the bike flat out ripped, tons of bottom for a 125, really really good midrange and a lot on top. The weight of the bike and the stiff motocross suspension just weren't my style, I'm used to plushly suspended heavy bikes with tame power. In tight woods the 144 lit up right about 1/3 - 1/2 throttle and wanted to jump out of my hands, when you're scratching each bark buster because the trees are so narrow this is no good. When I bought the 125 I thought I could make it something it wasn't, I really needed a 250 but wanted light weight, the power on the 144 is good, but not what I wanted. If you've got a tired 125 and want to breathe some life into it this is the best money you could spend on the bike in my opinion, if you've got any other questions just send me an email or a PM and I'll be happy to answer them.