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Discussion Starter #1
I have read several places that drilling out the main jet is not difficult. I was going to order a few from staidumyamaha but shipping is going to kill me. Almost 17 bucks for 2 jets and a bowl gasket. That's just for the shipping! I did't want to wait anyway. Got a few days off and want to tinker with the bike. Does anyone know the drill bit size needed to get the main jet to the 130 or 132.5 size? Also for the life of me I can't find a pic of the hole I need to drill out in the slide to improve throttle response? Thanks for all of your help guys!

Eddie
 

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I have read several places that drilling out the main jet is not difficult. I was going to order a few from staidumyamaha but shipping is going to kill me. Almost 17 bucks for 2 jets and a bowl gasket. That's just for the shipping! I did't want to wait anyway. Got a few days off and want to tinker with the bike. Does anyone know the drill bit size needed to get the main jet to the 130 or 132.5 size? Also for the life of me I can't find a pic of the hole I need to drill out in the slide to improve throttle response? Thanks for all of your help guys!

Eddie
I don't remember the size, but it ain't much. It's also oddball sizes, something like 11/132 or something on the one I drilled.
 

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Small drill bits in this size range need to run at extremely high speed to prevent scoring in the hole and it is still a hit and miss affair. If you drill your jet I bet you will be paying that $17 shipping soon after for a new one.

#130 main jet is standard in one of the carbs in an XT600, probably available in the breakers yard 132.5 available from Yamaha.
 

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Yea your probability right. But im just dumb enough to give it a try! Not happy with stock anyway. I have got pretty good gear but don’t think I can come up with that bit. It wont by anymeans be the first part I have ruined trying to modify. Thanks for the tip. Ill see how fast I can spin up the old jet drill press.
 

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I'm fortunate that my brother-in-law owns one of the finest tool-and-die shops in the U. S. of A. His crew builds tools for automakers that are so precise that the temperature of the product they build is specified so that laser-based measurement will be precise, and there is 0 tolerance. Kind of overkill for TW stuff. I used a laser-based device to create a nurb-based digital representation of a 128 jet and $275,000 CNC lathe to drill, then a nearly microscopic honing bit to reshape the funnel-shaped portion of the end of the jet and to smooth the walls of the hole. Overkill? You bet, but it was fun playing with the machinery.



I usually drill jets with a Dremel.
 
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I am somewhat aroused reading the specs of that machine! Now if you will excuse me I need to spend some quality time in the bathroom! Good Idea with the dremel I would like to make sure I dont wallow out the hole. Im thinking a bracket to bolt it to the drill press! Now that could be handy.
 

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I've drilled dozens of jets with a block of aluminum drilled and tapped to accept a jet, clamp the block in a vise, pull up a stool, brace elbows on the table, forearms against the vice, Dremel held firmly in both hands. Plenty steady enough.
 
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Welcome to the Forum!

Drilling out jets has some challenges:
1. If you do not record the mod, the stamped number on the jet will be misleading.
2. If the jet is not chucked into a lathe, the hole will not likely be straight.
3. If the drill bit is not new, poor quality, etc. the hole will be larger than the drill size.
4. TK jets are numbered the same as Keihin, so that a 130 jet is 1.30 mm, if I understand correctly.
5. If drilled properly that gives you the option of a 119 (56 drill), 133 (55 drill) or 140 (54 drill) main jet

Jets are currently $8.69 from JetsRUs.com

On a H-D Sportster 1200 Sport, I drilled the main intending to achieve 2.0 mm, but ended up with 2.03 mm.
This was in a machine shop, using a lathe.

Just my 3 cents
 
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