how to redrill main jet?

find a hardware store that sells jewlers drill bits, take your jet in with you & find the # bit that fits your jet. (probably a #70 bit) Then use the next size bigger to drill the jet. DON'T DRILL IT TOO BIG!!!
After you drill it one size bigger & put it back in the carb and take the bike for a ride.
If it seems to run a little better but not yet perfect then drill it again with the next size up until it runs good. AGAIN!!! DON'T DRILL IT TOO BIG!!!
If it runs worse, then you know you need to make the hole smaller.
 
Last edited:
Also after drilling you might want to experiment with the needle positions, this also makes a difference from idle to mid throttle, then the main jet takes over......
 
Howitt said:
you make the hole smaller by filling it with solder, right?
Click to expand...

Yep!!
Make sure you remove all the extra solder from both ends of the jet!!
(Make sure you don't go too small... running too lean is a very bad thing!)
 
Last edited:
I may have drilled my main jet too big. The engine lacks accelleration, has a slower top speed and has a slow idle. are these symptoms of a rich mixture?
 
I would try moving the needle clip UP a notch and trying it. It will make it leaner, idle thru mid range....
What size was it before you drilled it? What size did you drill it out to?
 
Last edited:
Ya' know after all the other riders have said there is one more thing that I would try. They made the stock air cleaner to except a certain amount of air for the carb. Bigger jet needs more air. A better air filter (one that breathes more) might made a big difference? It does on motorcycles. Can't hurt just don't loose the old one! Later Tramp(c)
 
yes it runs worse but in a different way. Before I drilled it, it seemed to be starved of fuel at WOT. Now it is fine at WOT but it just doesnt seem to run as fast, doesnt have the same quick accelleration and has a very slow idle.
 
Last edited:
It was stock before I drilled it .70mm and now I have it drilled to .85mm or .90mm. I purchased a set of drill bits from a hobby shop and they were ranged from #70 to #52. I found the bit that was the same size as the main jet hole and then went to the next bigger size. When I put the next size through it didnt seem to make the hole any bigger so I went up a few more sizes.

I will try to move the clip to the top notch and see how it runs.
 
You must log in or register to reply here.
Back
Top