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Mon Apr 20, 2015 7:15 pm

Hey all-

I came upon an older thread the other day that referenced my 30 PICT-3 carb with 227-1 modification state (for use on an autostick) as supposing to have a 112.5 main jet, 140z air correction jet, and 65 idle jet. My main and idle jets are correct, but the air correction jet is the more common 125z, and I can't find the 140z anywhere (probably not too many of them floating around.)

Would it be a problem for me to just drill this jet out to a 140z size? (As I understand it the number here refers to size of the hole in hundredths of millimeters, so a 125z would be 1.25mm, and the 140z would be 1.4mm.)

This carb along with my AE DVDA distributor has always seemed to work quite well, but I did still get the occasional flat spot on takeoff, and am wondering if having the correct air jet would compensate for this. Thx

Mon Apr 20, 2015 8:07 pm

sb001 wrote: but I did still get the occasional flat spot on takeoff

Possible Vacuum leak?

Mon Apr 20, 2015 8:11 pm

Hnoroian wrote:
Possible Vacuum leak?

I guess maybe, but if so it's so small it's not really an issue. It idles fine, takes off line fine, just sometimes a small flat spot through acceleration.

Tue Apr 21, 2015 2:02 am

Do you own a jet drill set? If you don't, I can almost guarantee you that you will screw up the jet, and who knows what size it will end up. I am not trying to pick on you, but the ability to accurately drill out a jet is an art form, and requires special tools. You could probably buy 20 different jets for the price of a jet drill set. Even then, you WILL screw up the first 5-20 jets that you try, unless you can feel the vibration of a mosquitos wings from 20 paces.

Of course you can always solder them closed when you screw up and re-drill them :shock:

Tue Apr 21, 2015 2:17 am

The flat spot won't be affected by the air correction jet anyway - that's more a top-end jet. And enlarging it will be leaning the top end slightly.

Tue Apr 21, 2015 7:24 am

Guess I'll just be leaving the 125z in there then--thanks for all the info!

Tue Apr 21, 2015 9:38 am

Micro-Mark sells 'precission drill bits'. If you want to go smaller the jet can be filled with solder and drilled out agian.

http://www.micromark.com/

Tue Apr 21, 2015 7:25 pm

Yes that site sells micro drills, but I didn't see any drills that would be considered JET drills. If you are going to drill out jets, then you need a set of bits that will correspond to known jet sizes. In todays market there is virtually no reason to drill jets. Back in the day (pre internet) you might show up at the track and find that the humidity level meant a jet change. If you didn't have the right jets, you drilled out what you had to work for that day.

Unless you have a HOT motor tuned to the nth degree, there is absolutely no reason to drill jets.

Tue Apr 21, 2015 8:44 pm

Precision drill bits change size in specific intervals as do jet sizes. How could jet manufactures guess the exact size jet my custom engines needs will land on? Weber and other vendors advise against it to sell more jets.

Wed Apr 22, 2015 12:57 pm

TSP,

You can do what ever you want in regards to drilling jets, but for the average person it is foolish. The first picture is of the jets for my Baja, it has a mild 2010 and I am running dual Solex 40PIIs. These jets are for that engine alone (notice the notes).

Then I have my 2110 DD 69 that is running dual webers 44s. I also have a 2 liter type 4 engine in my Squareback that is running dual ICTs (soon to be upgraded to 40 DCNFs) Each engine has its own set of jets. After that I have my 6 dirtbikes, Some of the engines run Mikuni carbs and some run Keihin carbs. Each brand has its own style of jets, so my jet collection is rather large. So since I have SOO many different engines that each require different jetting, why don't I just drill out existing jets and save money? Because 99% of the time when you drill out a jet, it will not come out to the size you desired. In the vast majority of the cases, the jet will be drilled out larger then expected, it may be egged shaped or totally wallowed out. Plus you have the cost of buying THE CORRECT JET DRILL SET.

Did I mention that I have a pretty good selection of drill bits? Well here they are.

Yet not a single one has ever touched a jet.

Thu Apr 23, 2015 10:20 am

I dunno about these but the Mikuni jets used on the Suzuki bikes I've had are rated based on flow on a test bench rather than diameter of the hole. As mentioned, with that small of a hole the tiniest imperfections anywhere nearby affect the flow.

Thu Apr 23, 2015 10:26 am

How do you plan to hold the jet still while running a drill bit through it?

A CNC mill with a machinist's small vise is the best, holding it in your hand is the worst.

Seal your leaks to eliminate your flat spot. Buy new jets if you must change them so you can go back if it doesn't help.

Thu Apr 23, 2015 11:43 am

Harleyelf wrote: How do you plan to hold the jet still while running a drill bit through it?

A CNC mill with a machinist's small vise is the best, holding it in your hand is the worst.

That is why I replied to this thread (maybe a little harshly). Most of the jet drill sets are essentially just steps of precision bits with a pen holder, and are designed to be used by hand. However, just like anything else, many of the sets that are sold today are junk. There is more to a drill bit then most people realize. You have terms like point angle, lip relief angles and clearance angle. All of these angles combined add up to how the bit will drill.

Since the jet is a soft material, once the drill bit has grabbed it will cut in the direction in which the bit was started. So cutting by hand in many cases will lead to the problems I described earlier.

Have I ever drilled jets - Yes guilty as charged. Have I ever screwed up jets when drilling them - Yes guilty as charged. However, this was back before Al Gore invented the Internet and now getting new jets has become an overnight solution.

Thu Apr 23, 2015 12:04 pm

Quote: How do you plan to hold the jet still while running a drill bit through it?

I used a regular nut to hold the jet and regular visegrips to hold the nut. :D I read a tutorial on how to redrill jets because I did not have the size I needed narrowed down and wanted to keep cost down. The whole process worked well. I kept cost down and I got my carbs fuel circuits where I wanted them.

Thu Apr 23, 2015 12:07 pm

aren't you putting the cart before the horse :wink:
unless you are keeping a secret.

Thu Apr 23, 2015 1:50 pm

All of the warnings and precautions of drilling out jets in my experience did not pan out.The sun rose the next day and so on.I wouldn't use one factory jet in one barrel and then use a drilled to size jet on the other though. The holes I drilled appeared to fit the shank of the bit well so I did not go any further than that for quality control. In other situations, chamfering the hole does not make a big difference so I did not heed any attention to it.

Thu Apr 23, 2015 5:35 pm

Harleyelf wrote: How do you plan to hold the jet still while running a drill bit through it?

A CNC mill with a machinist's small vise is the best, holding it in your hand is the worst.

Seal your leaks to eliminate your flat spot. Buy new jets if you must change them so you can go back if it doesn't help.

As I stated earlier the 140z I'm supposed to be using is impossible to find. Show me a link where I can buy one I might try it, otherwise I'm just putting the 125z back in and calling it a day. And I shouldn't have even mentioned the flat spot--it's really nothing. All I was wondering was whether the car would run better (and maybe why) with the correct jet.

Hell I can't even find anything to confirm it's the correct jet- it's just something I read in a thread on here:

http://www.thesamba.com/vw/forum/viewtopic.php?t=489336&start=0

Thu Apr 23, 2015 5:36 pm

60ragtop wrote: aren't you putting the cart before the horse :wink:
unless you are keeping a secret.

Wouldn't it be prudent to have everything else ready to go?