micro drill bits (tune accurately)
 

I found a website that sells any size you want within a nice range of sizes, for good prices and a low shipping charge. "New", "resharpened", and "good used" are available in most sizes.

Create Your Custom Drill set:-Sizes: .038" to .0785" - Drill Bits Unlimited.com

This is the next best thing to buying pre-drilled jets from jetsrus.

I was missing some drillbits between 108 (1.08mm) and 118 (1.18mm). So I ordered 110, 112, 115 and just for completeness sake I also added on a 120 and a 125 because they're cheap and to satisfy the "why not" factor. And perhaps maybe they're not as accurate as they say they are? Maybe I'll get a 126? Or a 124?

Turns out the actual sizes for the most part are .01mm smaller than advertised according to my digital caliper. So what I actually got are 109, 111, 114 but an accurate 120 interestingly enough, then lastly a 124.

The 111 came in handy when I was trying to tune a stubborn carb recently. My first "best guess bench tune" was with a 119 which, according to my previous experience, should have worked, but it turned out pig rich at part throttle cruise. So then I tried 118 and it made little difference. So I ordered the drill bits and only had to wait a few days in my area for them to arrive. I decided to start small with the 111 because you can always drill a jet larger, but you can't really drill them smaller, unless you're really clever. The 111 turned out really nice if not a hair lean, ranging from 13.0 to 14.0 AFR part throttle cruise. The carb seemed to run ok this time of year when it's warm but will require richer tuning for colder weather coming up. Plus I had some premixed 92 in there which I know reduces octane and also displaces some fuel. It might fatten up just enough once all the premixed stuff is gone. I really don't know because this is the first time I premixed on this setup and I think I used too much, however it doesn't smoke so who knows.

Anyway long story short is I still have a 114 drill bit I can try in this carb when the weather gets colder.

Then the secondaries are a whole other issue which I won't bore you with. But I think a 145 ought to do it. The 140 I tested first ran too lean and the current 148 is too rich at first at 10.0 as soon as they open, then leans out to 11.5 in boost. So pretty safe :) Again gotta consider the effect of premix and not set anything in stone just yet until it's all used up.

One last thing. If you guys are looking for a supply of jets to order so you can drill them yourself, look up jetsrus Hitachi pilot jets and main jets. The stamped sizes are .03mm off (a 110 jet is actually 107 or 1.07mm).

Good stuff here. Thanks Jeff.

I figured it would be useful. Makes a lot more sense than the way Holley started doing their more accurate jets with a suffix for their emissions controlled carbs lol. Terrible in my opinion. Just list the actual drill bit size that drilled the jet like I do. It couldn't be any easier than that. But then Holleys are the way they are. :rolleyes:

Back when I was more into motorcycles I would buy mikuni or kehini main jets by the bundle at the smallest size possible; then I would just drill them up to the size I wanted. I found that it is totally possible to go up in jet size; however going down in size is not.

Nice link. I might pick some up when I get back from vacation and FINALY turn the key on my car.

great post thanks for the link