Topic: drilling out main jets

[mmtsquid]

Cool!  I found a harbor freight close to work, so I'll get the bits at lunch.
I know there is a lot of negative response to drilling jets, , but the way I look at it, I've already bought 1 set of jets that are too small - I'll drill these, and if it doesn't work, I'll try ordering some.

[Jinxracing]

If you have to drill your jets by hand (shudder), at least do yourself a favor and use a decent bit. The odds of getting a good-quality drill bit of any stripe from Harbor Freight are 50-50 at best. Instead, go down to your local DeNault's or Ace Hardware and pick up 2 or 3 name-brand bits. They'll cost you $2 or $3 apiece and they probably won't have Cleveland Twist Drill, but they will certainly be better than anything you'll find at Harbor Freight

[ken74-550K0]

Because of the difficulty of finding larger jets, and on the recommendation of the people from motorcyclecarbs.com, I ended up drilling out my jets using I believe a #57 drill.  That worked out to 1.09 mm.  The drilling was done using a 6" Atlas lathe.

The end result was that the bike now runs great with the setup I have - velocity stacks and 4 into 1 pipe.  Before I drilled the jets, the bike hesitated badly between half and full throttle.

[Gamma]

Wonder if Bert Munro drilled his jets.

[crazypj]

For, let's say, a 135 main, you'd use a bit that measures as close to 1.35mm as you can.

Most of Honda's street bikes use the old fashioned diameter based system we have just described wherein the marking refers directly to the diameter of the hole.  However, since a change in diameter does not correspond directly to a change in flow (the ratio from memory is something like 4x, that is, doubling the hole size permits four times the flow, or something like that - However, a more scientific system is employed in racing carbs and incidently in most Mikuni carbs, wherein the diameter is a flow rating, in say, ccs per minute. 
http://home.earthlink.net/~motorstuff/tools02.html

You can pretty much guarantee Bert Munro did at some time.
 From the quote, Mikuni were based on Amal carbs so it should be possible to find old Amal race stuff from 60's which gave flow in cc's/min but with a specific 'head' of fuel ( I think 20" or 22" but not sure?)
PJ