I have a 2003 KFX50 ATV. I purchased it used. After getting it home, it started fine but with my kid (55lbs) on it, it would not go.

I pulled the carb, cleaned it and put in a new jet and new inlet fitting. After this it would go with him on it but would not go up a 40 degree hill?

Next I pulled and install a new ring and piston. The cylinder was fine and the piston had black on the sides. I fired it up last night for the first time. I is now louder has a little more power on the flats but still will not go up a hill??

Clutch? Bigger jet?

Thanks in Advance for the help/thoughts!

does it have a fuel filter

is the jetting correct, have changed and checked the plugs?

when you put in new pistons and rings, if it had blow by, did you go oversize pistons and have the cylinders bored...

does it have valves or is it a 2 stroke

does it have bad gas in it?

Also check for a plugged exhaust. the screen in the spark arrester gets carboned up and will cause the same problem. I got tired of cleaning it on our eton 50 and pulled the screen out. Not sure how the KFX is set up.

quote:

Originally posted by Quad daddy:
Also check for a plugged exhaust.

Good tip.