04 Kx125 Big Bore Kit

Don't even think of an Athena kit. They are junk, with no replacement parts available. Many good engine builders out there, get it done right, and it will work good and last a long time, and about the same money.

You must realize that the Athena cylinder is based off their 125 cylinder and is going to have port time issues.

When a 125 cylinder is bored out all the ports are lowered, and often the exhaust port window is narrowed, because of the angle the port enters the bore. I've measured the boost port in an Athena cylinder to be 6.5mm lower than stock for a yz144, that's huge.

You want a engine builder that will reset the port timing for optimum performance or you will get a motor that dosen't rev well at higher rpm's like a 125/144 should.

Ericgorr.com You can thank me later.

if i was going to dump money into a small bore 2 stroke id get a ktm 150. but ive riddden 144s and they never seem that good or worth the effort. plus if you wont fool anyone bc a 144 sounds like a 250 more than a 125. if u wana go bigger try a 134 port and polish and race gas btw i heard ericc gorr sucks from alot off ppl