Piston sizes hi, im just wondering how important piston sizes are? the shop could only give me an A size piston but i think my barrel is a C. Yz125 2007.thanks

This venturi (throat) size and the jet size are different...the smaller carb will give more bottom end.... the larger carb will make it run better mid range and top end...

BOTH must be jetted correctly...by someone that knows how!!

Hi the sleeves cannot be removed if they need to be re-bored you need to sent the top casing to a machine shop with a new piston so they can bore it the right size. Regards Jim...

Ebay has piston , ring and gasket kits for about $30. The barrel is cast iron, so if there is no lip a simple hone may do.
I f the barrel is pitted , you will need an oversize piston kit, and a machine shop to bore the barrel to a bigger size.

Hope this helps ??

If the bike has been seized up it's important to check out the piston and cylinder head. It's a good learning experience and not that hard a project. Remove the seat, tank, pipe and maybe the carburetor and you should be able to get at the head bolts. Pull the head and inspect the top of the piston and ring area. Rings usually get stuck to the piston so there is not any compression. Pull the jug and more than likely there will be alloy from the piston transfered to the cylinder heard.
Take it to a bike shop or automotive machine shop that can hone it to first over. Purchase new 1st over-sized piston and matching rings. Re-assembly and replace all gaskets.
Thanks for contacting FixYa,
TF

you have to buy a new bore kit which u fetch u around 5k

its not that easy here are some of the things u need to know

* solid or hyd cam
* roller or flat tappet
* valve installed hieght
* rocker ratio
* cam lift

this is just a few things go to a head shop and they will choose the right ones