I would check the compression. It is supposed to be between 140 and 200 lbs. I had the same problom with my ATC250SX. I had to hone the cylinder out to 25 thousanths and get new piston rings for it






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My Machine
Honda ATC250SX Custom Built with 8 inches of rear wheel travel. Cobra pipe and bore out 25 over. Would like to get a 300 jug kit for it.

 

ok i finally got to ride the bike after flipping the reeds. it runs much better but still has a low end problem. compression is good. the reeds still have a small gap between the box and the reed itself. i think i am going to order new reeds. what are the best reeds to get for this setup. are delta v-force reeds wothe the money?

 

Sure, Delta V-Force are excellent reeds, also expensive!
If you want reeds for low-end/mid-range, try getting some stockers from a '98 CR250. Bolt right in and work extremely well.
Or, like I said, a quick and inexpensive fix is to install some new Boyesens and they work just fine.

<u>You want to do a proper plug chop!</u>
First, install a fresh plug that has been gapped properly.
Warm it up, ride around easy for about 10 minutes.
Head away from camp to a point where on return trip you can tap out a high gear; 4th on up should do it.
Nail it wide-open-throttle (WOT) and hit the highest gear you can. Hold it WOT for a "10" count.
Now, all at the same time, pull in the clutch, shut off the motor, keep WOT until engine stops completely, and COAST to a stop, don't let out on the clutch and turn the motor at all!
Now pull the plug and check it. You want a brown plug. White means too lean and you need to increase main jet size. Black or oily and you're too rich and need to go down main jet size. Change only one size jet at a time and do another chop EXACTLY the same way until you get it right. It may be a pain, but once you dial it in, you're good for a long time.
No one can tell you exactly what jet size to run for several reasons; every engine has different quirks, not everyone is at same elevation you are, or has the same humidity, or the same ambient air temperature or even the same fuel/oil mix. You have to start out and do this yourself.

If you're bogging off the bottom-end of the powerband, you can also do a plug chop for low-end. Do it the same way except use only 1/4 throttle. This is a good way to check your pilot jet. Same things though, black=too rich, white=too lean.