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CB125 Street Tracker

CB125 Street Tracker build Part 1

Picked up a stock 1975 CB125 with low compression and a junk front end.

Stock, unmolested CB125


I decided to build a street tracker with the stock 125 engine modifed as much as safely possible.

Sourced this145CC cylinder and piston kit for a cb145, which is a euro version i guess? Bored cases to accept the bigger cylinder and it worked out perfect.

Next was the head, I used the head from an 86-87 ATC200X, milled .080″. This is too much! I had to cut a lot of material from the head and the piston for clearance.

In order to use the stock ignition system, you have to cut the end of the camshaft off. You want to cut the cam where the machined groove is,about 3/8″ from the end, cam chain side. Then you can assemble it like it was still stock.

Ordered this chinese knock off of an XR200 carb with throttle cable and K&N filter, and changed the main jet to a 75.

CB125 ATC200X ( xr200 ) Head and Carburetor

I ditched the stock muffler and went with an Emgo ,
type but it iwas made for a larger diameter head pipe, so I welded a piece of 1-1/4″ pipe to it so I could get the larger diameter needed.

IMG_1727              IMG_1728

More to come.

CB125 Street Tracker
CB125 Street Tracker build