drilling out carb jets

[Anonymous]

I want to experiment --i have a stock set od mains in a set af carbs that i have--they are about 102s i want to make them 160s--first of allwhat does the number 102 04 160 mean except that one is larger-i mean in what sort of measurment are the calculated with ??

 

[moto_dan]

Re: drilling out carb jets

I want to experiment --i have a stock set od mains in a set af carbs that i have--they are about 102s i want to make them 160s--first of allwhat does the number 102 04 160 mean except that one is larger-i mean in what sort of measurment are the calculated with ??

I think it's like this 160 = 1.60mm, but I wouldn't bet the farm. 1.60 mm = .062". Converting from mm to inches (mm /25.4). Then you have the jet kits that use their own scale. That's my guess...anyone else?

 

[SqDancerLynn1]

I would think part # it is more of a flow rate than a physical size

 

[Anonymous]

Well at least you guys are thinking of something--i can think of nothing

I found this info but it still doesnt answer my question

http://www.snowtechmagazine.com/articles/dontuse/dontuse.html

 

[Anonymous]

I just sent a letter to mikuni-maybe they will helpay be some sort of secret -- they may want us to know the gpm flow but not the physical size of the orfice--i remember seeing a set of thin wires for cleaning jet orfices --I wonder if any one has something like these to measure with??

 

[moto_dan]

Here's a little help...maybe

http://home.att.net/~tele1/jetsconversionchart.htm

 

[Anonymous]

Here's a little help...maybe

http://home.att.net/~tele1/jetsconversionchart.htm

THAT DIDNT HELP A BIT--IT TOTALLY ANSWERED MY QUESTIONTHANKS LOTS

 

[Anonymous]

Scotty, I was considering the same thing. I was rejetting my 850 and a friend gave me a box of different size jets to try. He had 4 full sets of 115's (stock) and I was thinking of trying to drill a set of them out. Dentist's drill bits are very small. I was going to ask my dentist next time I go for a cleaning if he had some old ones to play with. If I could match them up with some different size jets then you could make a set of jets any size you wanted, except they wouldn't have a chamfer on the edge.

 

[Anonymous]

Scotty, I was considering the same thing. I was rejetting my 850 and a friend gave me a box of different size jets to try. He had 4 full sets of 115's (stock) and I was thinking of trying to drill a set of them out. Dentist's drill bits are very small. I was going to ask my dentist next time I go for a cleaning if he had some old ones to play with. If I could match them up with some different size jets then you could make a set of jets any size you wanted, except they wouldn't have a chamfer on the edge.

Maybe this project is just wishfull thinking

 

[saaz]

No, it is not wishful thinking but reality!!

I have a number of sets of jets drilled out from standard to what I wanted. I had the standard ones plus some I bought to play with. When I did the motor up I needed some serious size increases.

Anyway, I had a carb place do it. Anyone who does performance mods to car carbs would do this all the time. If you know someone with the right size drills, use that.

I have a set of #95s drilled to #120s

Scotty, you are just froward thinking or rediscovering the past.....I have not mentioned this before because I thought everyone would have been advised about doing this when playing with jets......

 

[Anonymous]

A mate at work drills his own jets. He uses drills that are not size listed but numbered. He puts the drill bit in a holder and spins it between his fingers to enlarge the existing.

When I was building two stroke race motors back in the '70s I would enlarge jets with a piece of brake inner cable wire and grinding paste. Just find some thin cable wire the will fit the existing jet, dip it in the paste, and slowly work out the jet, experimenting until you get it big enough.

It sounds dodgy but we did some magic things to motors in those days with such home-made methods. Anyway, this method came from the famous Fred Bockle's bike shop in Wollongong where I used to buy my bikes and bits in my younger years. Fred was a master magician of motor bike engines, and his brother, Ari, the same with VWs.

Kim

 

[hoyterb]

Hi Scotty It's time you bought a set of "number" drills and a pin vise.Most auto parts stores can get them.I got mine from Snap-on tools years ago.When you drill use the smallest drill that won't go throught jet.Drill absolutely straight through jet.A slight wobble will give you inconsistent jet sizes.Have any questions just ask. Brian H.

 

[Anonymous]

Guys, I've tried to hold back but I can't resist any more....drill your own jets? WHY??? I mean, sure it's possible, but....First, the jets you buy are darn near perfectly machined. No burrs, no wobbles, no oblong holes. By hand there's a pretty good chance at least one out of the four won't have the same flow rate as the others. And what happens if you drill too big? You'll have to go buy more jets, which I assume is what you were trying to avoid in the first place. And then how do you identify the jets you've drilled out? You could wind up with a couple of sets that don't match the markings on them...very confusing...!!!! All to save a few bucks? I'd rather be riding!!!

Just go buy a couple sets of the next few sizes and move on to the next project!!

 

[Anonymous]

Guys, I've tried to hold back but I can't resist any more....drill your own jets? WHY??? I mean, sure it's possible, but....First, the jets you buy are darn near perfectly machined. No burrs, no wobbles, no oblong holes. By hand there's a pretty good chance at least one out of the four won't have the same flow rate as the others. And what happens if you drill too big? You'll have to go buy more jets, which I assume is what you were trying to avoid in the first place. And then how do you identify the jets you've drilled out? You could wind up with a couple of sets that don't match the markings on them...very confusing...!!!! All to save a few bucks? I'd rather be riding!!!

Just go buy a couple sets of the next few sizes and move on to the next project!!

We like to play Bill--some of us couldnt do it when we were younger. Believe me its not a money thing--a good drill bit costs almost as much as a jet

 

[Anonymous]

Okay doky, if you're experimenting for the joy of experimenting, and not expecting miracles....But here's my 2 cents worth for going about it. I would make a little fixture to clamp in my drill press to hold the jet very securely. Accurately position the jet under the drill press, using a drill bit that matches the existing hole. Then drill it out with the new bit....keep drill RPM very high, and light pressure, maybe kerosene for a cutting fluid. The fixture would position each jet uniformly and accurately. .... Gotta avoid getting burrs. After all 4 are drilled, I'd maybe even rig up a test on each jet to see how much flow you get through each one. Maybe a bottle suspended a foot or so above the jet and plastic tubing to the jet ....run kerosene through the jet, to see how long it takes for a quart of kerosene to empty out through the jet. That'll give you a fairly decent idea of the flow rate for each jet. Maybe do the bench test on the original jets first, just for comparison. I'd use kerosene instead of water for the flow test, it'd match the fluid properties better. Gasoline is too flammable for me when trying these kind of experiments. Good luck. 8)

 

[saaz]

Easier way is to drill until you get the size right, then invest in the right jets. Saves having to try a few sets of jets before you get the combination right. mIne are drilled out, have been dyno tuned and are ok after 18 years or so.

 

[Anonymous]

drilling jets

drilling jets

Drilling jets ??? Are you guys loonie ? At $2.50 a piece why bother . One day you may want the old size again. Besides these are precision made pieces that you could not hope to duplicate consistently unless you had a very good quality lathe to work with, not a hand drill or drill press. Any motorcycle shop will be able to supply them or find you mikuni distributor in the yellow pages or www.sudco.com online or ride with four totally different jet sizes . And you guys thought tuning was hard with the right parts

 

[Anonymous]

You sound like an engineer, Nashville Bill. :wink:

I also like to experiment, and would rather pay 25 bucks to find something out for myself, than to pay 12 bucks to have someone do it for me! 8)

A fixture in the drill press is a great idea, but a lathe is a better one, if it is available. That way, the hole will be centered all of the time.

As far as measuring the existing orifice goes, machinists use pin gages (the look like drills but are smooth) They come in sets, and are generally sized in .001" incriments. They are usually .0001 smaller than the size marked, so you can actually fit it into the hole you are measuring.

Regarding drill sizes, they generally come in three size designations, numbered (or letter for big ones), fractional (ie 1/8"), and metric. If you really want to dial in the flow, don't limit yourself to just numbered drills. Looking at my chart of standard drill sizes, it reads as follows:

#80 (.0135")
.35mm (.0138")
#79 (.0145")
1/64 (.0156")
.4mm (.0157")
and so on

Smaller drills are available too. They might come under the heading of Jewlers Drills or Watchmakers Drills. I'm not familiar with standard sizes below #80.

If you really want to get fancy, you can order a reamer ground to within .0001" of any diameter you want. Of course this isn't going to be cheap, but it is possible.

You could also pick up a countersink and add a chamfer, like the Mikuni factory jets. But without a lathe, it would probably be hard to get the chamfers on all four jets close to the same size.

A store that sells machine shop equipment and supplies can set you up with whatever you need. McMaster Carr is usually a more convenient source, and they have a web site.