Drilling Jets Size Question

Alright so finally got some mini drill bits in, and got the other set of stock jets out and cleaned em up and got em ready to drill. Now I have a few Questions Im running a kz550ltd with harley mufflers and pod filters and the tk carbs, so what size main and pilot should I shoot for. From what I read I should probably go up to a 37 pilot from a 34 correct? so I would use a #79 bit? Now about the main what size should I shoot for a #96 main or more? My bits only go from 61-80, so what size bit should I use and what size does it correspond too?

If you are talking about the C model LTD, then you have the TK-22 carbs.

Stock pilot jets are #32 (.32 mm). Your #80 bit is about .34mm. Your #79 bit is about .37mm. I don't really know what harley mufflers are like, and which pods you have, but 34 or 37 will probably work. Turn the mixture screws out to about 1.5 to 2 turns out.

Your stock mains are #92 (.92mm). I'd start out with drill size #62. That's about .965mm or a #96.5 jet.

The #61 bit will get you to #99 main jet.

If you bought the K&L rebuild kits, you should have adjustable needles now too. I'd go to the third slot from the top on the needle if you feel hesitation at steady 60mph cruise in top gear. (That is, with a rock steady throttle position.)

Oh, Brother, Here we go again. What is so hard about spending $12 on a set of original jets. This subject must have been covered in a minimum of half dozen threads with in the last year. For the umtenth time, It is not just the size of the hole but the length of it and the angle of the taper on each side. Once you drill the hole, you must flow Gas threw it at 10psi to see what the flow rate is. Yes it must be gas because there is no other liquid with the same specific gravity. This was all covered in past threads. Just buy the right jets from Z1 and do it right. You will have to do it anyways after you have drilled yours.

otakar wrote:

Oh, Brother, Here we go again. What is so hard about spending $12 on a set of original jets. This subject must have been covered in a minimum of half dozen threads with in the last year. For the umtenth time, It is not just the size of the hole but the length of it and the angle of the taper on each side. Once you drill the hole, you must flow Gas threw it at 10psi to see what the flow rate is. Yes it must be gas because there is no other liquid with the same specific gravity. This was all covered in past threads. Just buy the right jets from Z1 and do it right. You will have to do it anyways after you have drilled yours.

No one is changing the length or the taper or anything but the orifice diameter. What is so hard to understand about drilling a hole? That's all it is. It does not take a machine shop to make a hole a few thousandths of an inch bigger. The tapers etc all stay in tact.

I've been doing this for ten years and I've done the testing with a wideband o2 sensor to confirm AFR. My data is on KZR. Go look at it.

And for the umpteenth time, my response is: give me a link to TK-22 pilot jets or main jets that are bigger than stock. I notice everyone suddenly gets quiet after that.

And don't give me some Keihin replacements that look completely different, because you already stated that you can't use jets that use different length etc.

loudhvx wrote:

otakar wrote:

Oh, Brother, Here we go again. What is so hard about spending $12 on a set of original jets. This subject must have been covered in a minimum of half dozen threads with in the last year. For the umtenth time, It is not just the size of the hole but the length of it and the angle of the taper on each side. Once you drill the hole, you must flow Gas threw it at 10psi to see what the flow rate is. Yes it must be gas because there is no other liquid with the same specific gravity. This was all covered in past threads. Just buy the right jets from Z1 and do it right. You will have to do it anyways after you have drilled yours.

No one is changing the length or the taper or anything but the orifice diameter. What is so hard to understand about drilling a hole? That's all it is. It does not take a machine shop to make a hole a few thousandths of an inch bigger. The tapers etc all stay in tact.

I've been doing this for ten years and I've done the testing with a wideband o2 sensor to confirm AFR. My data is on KZR. Go look at it.

And for the umpteenth time, my response is: give me a link to TK-22 pilot jets or main jets that are bigger than stock. I notice everyone suddenly gets quiet after that.

And don't give me some Keihin replacements that look completely different, because you already stated that you can't use jets that use different length etc.

Im with you there. That was my problem no jets locally, but I have extra stock jets, so I figured why not. Ive drilled dirtbike jets before so I know drilling them at home is perfectly fine.

I don't recognize those jet numbers, but here is where I get my jets: Try Z1 first. If they don't have them, Pat's small engine supply had the biggest selection of jets I ever saw.

www.z1enterprises.com/

www.psep.biz/store/mikuni_pilot_jet.htm

www.psep.biz/store/mikuni_main_jet.htm


www.allensperformance.co.uk/mikjets.html

Z1 does not have them. Mikuni does not make them.
The closest are Keihin mains, which I have no problem using. But they considerably different from the TK jets. They work but are different. I have not yet found a Keihin pilot close enough.

Either way, it doesn't matter because I have a slew of stock TK jets. If they work drilled, why not use them?

Did you guys try SUDCO? Also I believe that the ZR750 Keihin carburetors have the same spread as the 550. That is if you want to find carbs which you can find parts for. I do apologize for the previous posting. 1) I did not realize that we were talking of anything other than Mikuni. 2) I also did not realize until now that TK is so difficult to find parts for. MY BAD :blush: Open mouth-Insert foot, I am good at that sometimes.

otakar wrote:

Oh, Brother, Here we go again. What is so hard about spending $12 on a set of original jets. This subject must have been covered in a minimum of half dozen threads with in the last year. For the umtenth time, It is not just the size of the hole but the length of it and the angle of the taper on each side. Once you drill the hole, you must flow Gas threw it at 10psi to see what the flow rate is. Yes it must be gas because there is no other liquid with the same specific gravity. This was all covered in past threads. Just buy the right jets from Z1 and do it right. You will have to do it anyways after you have drilled yours.

what is wrong with you guys? Otakat is right. even if you have a really good drill press you will never achieve what the carb company's achieve. the drills you can buy are never going to give the accurate orifice size of a factory jet. just buy factory jets.

hoghaterkaw wrote:

otakar wrote:

Oh, Brother, Here we go again. What is so hard about spending $12 on a set of original jets. This subject must have been covered in a minimum of half dozen threads with in the last year. For the umtenth time, It is not just the size of the hole but the length of it and the angle of the taper on each side. Once you drill the hole, you must flow Gas threw it at 10psi to see what the flow rate is. Yes it must be gas because there is no other liquid with the same specific gravity. This was all covered in past threads. Just buy the right jets from Z1 and do it right. You will have to do it anyways after you have drilled yours.

what is wrong with you guys? Otakat is right. even if you have a really good drill press you will never achieve what the carb company's achieve. the drills you can buy are never going to give the accurate orifice size of a factory jet. just buy factory jets.

Ok, I will type it once again.
There are no factory jets available other than stock.
If someone can provide a link, that'd be great.

Also, EGA tests and wideband o2 sensor tests have shown that +/- one jet size is virtually undetectable, and the margin for error on drilling will less than that as long as you don't sit there for more than a second with the bit.

Also:

A .92mm jet created using a #62 drill bit does not have to flow EXACTLY the same as a 92 mikuni/kehien/ect factory jet. Technically...it doesn't even have to be close.

It just has to flow what you need. If you are lean, increase the jet size until you get the result you are looking. Who cares whether it flows the same as the factory jet with a comparable number.

I've drilled jets for years and never had a bother with it. It seemed to work just fine, and I did it for many clients who asked and seemed fine with it as well.

Until one day I met a guy who knew exactly why he would'nt drill them ever again.

This friend had an electronic thermister system on an engine that used complicated peltier cooling units (voltage controlled cooling). Individual precise electronic thermometers all over the place.

He couldn't account for small variations in the voltage required for the peltier units. no matter what he did, it didn't matter. he could syncronise everything just fine. Produced lots of smooth power, and no issues at all.
But it had to be perfect!

Then he remembered... he was using press drilled jets.

Installed OEM jets, and SNAP. The units voltages were literally identical.

I don't drill jets anymore. But not because it doesn't work, or is risky or anything. I can afford new jets (who cant really), and I'm a stickler for small variations.

Many schools of thought, none wrong per say. But this story has had a 100% new jets purchase rate from all of my clients whom I tell this story! :laugh:

Cheers to all!