Drilling out jets

badspree · Post by **badspree** » Tue Jul 18, 2006 12:40 am

Hi, I am doing a cold air intake with a chevy v8 k&n style oil breather, and building a custom exhaust from a 49cc pocket bike with an expansion chamber. I have already ported the intake. I thinking I will have to run a 70-72 main jet, but the largest ones I can find are 68's. Does anybody know how, or what drill bits to use to drill out the main jet to this size. Also if anybody have a setup something like this, what are you running for jetting.
thanks,
Badspree

fulltilt · Post by **fulltilt** » Tue Jul 18, 2006 7:57 am

I had the same set up with the pulley mod, a milled head, and a 68 jet. Wouldn't run. The intake system needs some restriction. So does the exhaust in my opinion. Try the pulley mod and fire clean the exhaust. Those were the most significant contrinutors to my 35 mph.

badspree · Post by **badspree** » Tue Jul 18, 2006 2:59 pm

Your's probably didn't run because you need a significantly larger jet than a 68, more like a 70-80. With the amount of difference in air (which is large) you need a significant amount more fuel. If anybody knows what drill sizes to use to get the main jet into the 70's, please let me know.

se50 · Post by **se50** » Tue Jul 18, 2006 4:05 pm

I tried it on my Elite 50. It was running too lean with a UNI filter and leaky exhaust on the stock "82" jet, so I drilled it out with a #60 drill bit, the smallest I had. Worked like crap. It made that jet the equivalent of a 100 or so, by Keihin's jet scale on that carb (about 1mm), and now, no matter what I do with the air screw, even take it out, it runs very rich. Accelleration is great, on a 95 degree day, when I've been dirt riding with it for 20 mins and have the engine hot, but it just bogs down at wide open. Lesson learned-
Unless you have a complete set of tiny number drill bits, don't drill the jet out.

tonrogs · Post by **tonrogs** » Tue Jul 18, 2006 10:26 pm

use this table here to convert drill # to a jet size....
http://en.wikipedia.org/wiki/Drill_bit_sizes
Now, how to read it. Ex. A #64 drill bit would produce a jet size of 91 and a #70 a jet size of 71. Guage is your numbered drill bits and jet sizes are the metric values.

Post by **noiseguy** » Wed Jul 19, 2006 12:38 pm

The #'d bit info's in Adv Tech Docs too, on Drilling Jets.

Also, have heard that you can refill the jet holes with lead solder and redrill them in a pinch. Just a thought.

badspree · Post by **badspree** » Thu Jul 20, 2006 4:29 am

Thanks for the table, that's exactly what I am looking for. I have got (2) #68's coming from servicehonda so I can screw one up. If I get it to run out I'll let everybody know.
Thanks!

badspree · Post by **badspree** » Sat Jul 22, 2006 1:19 am

Well, I got my exhaust all welded up and am now hitting 36-37 mph. Didn't rejet, didn't do anything with the air intake. I am extremely happy. If anybody can post pictures on this site, let me know. My exhaust is baddddd assssss, way nicer than anything else I've seen anybody else build (my opinion)
Later

Post by **noiseguy** » Sat Jul 22, 2006 5:48 pm

Email me the pics and I'll post them.

se50 · Post by **se50** » Sat Jul 22, 2006 8:14 pm

You mention a leaf blower supercharger. I have a better/different/easier idea-
Electric inflator. The type that goes into a car lighter socket. That would be a lot easier and smaller, and you could turn it on and off easily.

badspree · Post by **badspree** » Tue Jul 25, 2006 3:35 am

Does anybody else think that the leaf blower charger would possibly work? I've been racking my brain trying to come up with a way to get the fueling down. They only produce 2-3 psi max, so I don't think that would blow up the motor, but it would be funnier than * to see it done. I'm going to be purchasing a new scooter next year, so this is kinda just a toy for me anyways. Anybody got any input on what is the best new scooter to buy for tuning and performance? I would like to stick to 50cc?