Drilling jets bigger?

It has been suggested to me that if I have a hard time finding bigger jets for my CV34's, I can drill out the old ones.

Okay, but this begs the question: What drill sizes equal what number (size) jets? Is there a listing somewhere showing jet numbers and the actual size of the holes?

Thanks!

Every jet I've measured follows that the size is in hundredths of a millimeter. That's for Mikuni, Keihin, and TK carbs. Here's a comprehensive drill wire gauge:
en.wikipedia.org/wiki/Drill_and_tap_size_chart

You can probably just order jets for those carbs.

I agree, I can't see you having any problem obtaining jets for the CVs. I was once told however that a 1mm drill bit equates to a 150 jet size, how correct that is I don't know. The problem is that once you've drilled it there's no going back, you can't even use the bike while you get more jets as you've just knackered the originals.

Well, I guess my question should be, what are the stock pilot and main jets sizes in a stock '82 KZ750H3 four, and what size is each step up from that?

You have those stupid Kaihins. Those jets are hard to find. The stock main jet size is a 110. That is equivalent to a Mikuni 99.5 so call it a 100. Now you can replace the jets with redly available Mikunis. The size would depend on what modifications you did to the engine including filters and tail pipe. You can figure that you can automatically go two sizes larger just because the stock jets were very lean. so 115.0 is a good start. Don't mess with the pilot jets. There is no reason to do it. My bike is built like crazy and I still run stock pilots. Don't let anyone tell you that you cant put Mikuni jets in Kaihin carbs, I do it all the time. The thread is only a tiny bit off but they will seat and from that point on they will go in all the time. I just use one old Mikuni jet to dress the threads in all the carburetors and than I install the required new jets.

You have those stupid Kaihins


dont let OMR hear ya say that.....:laugh:

110 is stock? Okay, does anyone know the actual diameter of 110 jets?

The bike is a 1982 KZ750H3 four. It is bone stock, although I am doing a few bobber mods. I want to go to pods as I want the space that the airbox uses for something else, and because frankly, I like the pod look. I will also drill the stock mufflers with 6-1/2" holes around the main outlets. That is all the mods the engine will receive.

I've drilled lots of auto carb jets without problems and have lots of drill sizes. I figure why bother to go through the hassel of ordering jets when I can easily open up what I have. I just don't know what size to open them up to.

What would be a good ballpark pilot/main jet size for this (or leave the pilots alone as mentioned?)?

Why? Dose he have those STUPID STUPID Kaihins also? :lol:

Z1 sells the Dynojet kit. It's expensive, but you pay for the research. It includes 4 adjustable needles for easier tuning.
www.z1enterprises.com/detail.aspx?ID=4038

polkat wrote:

110 is stock? Okay, does anyone know the actual diameter of 110 jets?

The bike is a 1982 KZ750H3 four. It is bone stock, although I am doing a few bobber mods. I want to go to pods as I want the space that the airbox uses for something else, and because frankly, I like the pod look. I will also drill the stock mufflers with 6-1/2" holes around the main outlets. That is all the mods the engine will receive.

I've drilled lots of auto carb jets without problems and have lots of drill sizes. I figure why bother to go through the hassel of ordering jets when I can easily open up what I have. I just don't know what size to open them up to.

What would be a good ballpark pilot/main jet size for this (or leave the pilots alone as mentioned?)?

They are not measured in size. They are measured in flow rate. size 100 = 100cc/min. That is on the Mikunis. Iam not kidding when I say that no one knows how the Kaihins are numbered. It is not just the size of the hole because three or four sizes might have the same hole but the length of the hole is different and the taper on each side is different. That is how the jets are fine tuned. On the average the difference between sizes is approximately .001" To give you a perspective, a #58 (.042") bit would be a 110 jet but the length of the hole now is the other variable, and that is if you ignore the tapers at each end.

loudhvx wrote:

Z1 sells the Dynojet kit. It's expensive, but you pay for the research. It includes 4 adjustable needles for easier tuning.
www.z1enterprises.com/detail.aspx?ID=4038

If this guy wants to drill jets, he dose not want to spend the $8 on the four jets. How do you expect him to spend $100 on a Dynojet kit. :ohmy:

otakar wrote:

polkat wrote:

110 is stock? Okay, does anyone know the actual diameter of 110 jets?

The bike is a 1982 KZ750H3 four. It is bone stock, although I am doing a few bobber mods. I want to go to pods as I want the space that the airbox uses for something else, and because frankly, I like the pod look. I will also drill the stock mufflers with 6-1/2" holes around the main outlets. That is all the mods the engine will receive.

I've drilled lots of auto carb jets without problems and have lots of drill sizes. I figure why bother to go through the hassel of ordering jets when I can easily open up what I have. I just don't know what size to open them up to.

What would be a good ballpark pilot/main jet size for this (or leave the pilots alone as mentioned?)?

They are not measured in size. They are measured in flow rate. size 100 = 100cc/min. That is on the Mikunis. Iam not kidding when I say that no one knows how the Kaihins are numbered. It is not just the size of the hole because three or four sizes might have the same hole but the length of the hole is different and the taper on each side is different. That is how the jets are fine tuned. On the average the difference between sizes is approximately .001" To give you a perspective, a #58 (.042") bit would be a 110 jet but the length of the hole now is the other variable, and that is if you ignore the tapers at each end.

knowing this, it escapes me how someone can do a bike build and try to cheese out at every corner....no offense,
but ya got to cut loose with some cash if you are going to be successfull....if the cash isnt there, wait till it is.....