Jet 42 to drill bit size chart2/6/2024 Then I took another drill and it measured 42(.016) but this was too large for the 45. ![]() I have some small drills and the 40 turns out to measure 37 (.014). I have found I'm 12.5 on the idels running 45 idles so I tried some 40's and the car would not run. View original topic: Jet size vs drill size If possible, it is a good idea to keep a stock jet or two around just :: View topic - Jet size vs drill size Forumsįorum Index -> Performance/Engines/Transmissions -> Jet size vs drill size Once the jet is filled, simply re-drill it to the size you want. Brass jets can be heated with a torch and then solder can be used to fill the jet. If you go too far when drilling a jet, it is possible to go back to a smaller size. Let the drill bit work it's way through the jet to avoid breaking the bit. Just as hand drilling, apply only gentle pressure. If a jet is drilled at an angle or if the bit wobbles the jet will actually be larger than the size you are aiming for. It is very important to drill straight in order to get an accurate jet size. If you wish to drill the jet with a drill press, you need a vice or clamp capable of holding the bit at a 90 degree angle from the jet. If you break a bit off inside of a jet, you may not be able to get it out, and even if you do you just broke the drill bit that you need. Small drill bits are very fragile and break off easy. Spin it carefully and don't push it into the jet. Don't try to force the drill though the jet. Hand drilling is pretty simple on most common brass carburetor jets, but may not work on jets made from harder materials. Hand drilling simply involves holding the drill bit in your hand and gently turning it to drill the jet. This chart is intended to get you on the right track, but may not be completely accurate.ĬLICK HERE FOR A PRINTABLE VERSION OF THIS CHART.Īlright, so you've got your new drill bits and you're ready to start tuning, but how do you drill a jet? There are two pretty common methods used for drilling jets, hand drilling and using a drill press. For this reason, it is said that no exact comparisons can be made with this data. Meaning, a jet from one manufacturer that is tapered or chamfered in a different manner could flow more or less than another manufacturer's jet of the same diameter. The way a jet is made changes the amount of flow it is capable of as well. Keihin jets have been very close to actual size from my experience. I've been unable to find any good information on how Keihin determines it's jet sizes. Mikuni is said to use flow numbers rather than actual size for it's ratings (100 = 100cc per minute). DynoJet is supposed to be the actual size of the jet (100 = 1.00mm), although the numbers on every chart I've seen are close to accurate there, but not 100% correct. Apparently different manufacturers use different rating methods for their jets. That seems simple enough, but unfortunately it gets a little more complicated and confusing. There are more fractional and metric drill bits available, but this should cover most needs for small carburetors. The chart below shows drill bit sizes by number, fractional standard, and metric units converted into actual size and metric jet size. Here are a couple of links to affordable drill bits suitable for drilling jets. You'll need to get a selection of proper bits, most likely numbered drill bits. Don't just go out and grab any drill bit that looks small enough to you. Many carburetor jets can be drilled to get you in proper tune. There is an option that can save you money, and save you from waiting on the mail carrier to drop off your new jets. If you own or work on more than one type of scooter or ever swap carburetors, the jets you bought tning the first carburetor may not work and then you're stuck spending more money on jet kits. You may also need different jetting for summer or winter termperatures and other variables. Jet's range in price from roughly $2.50 up to about $10 and sometimes you'll try quite a few of them to get the tune right. ![]() It's great to have a stockpile of jets lying around when tuning a carburetor, but not everyone wants to spend that kind of money.
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