Anyone ever drill out jets to the size needed?

[rscotth]

Like most people here I can't leave anything stock and love to modify "vehicles" of any type. While sitting around waiting for my jets and other items to come in I found a guy that mentioned he has drilled out jets in the past with much success.
I am a firm believer of getting the right parts and tools for the job but if your careful it can be done professionally. What really helps is a small drill press and "Wire Gauge" drill bits. I couldn't find a lot of common sizes like 112, 115, 125 ect but here's what I have collected so far and maybe it will help someone get their grounded scoot on the highway a little sooner.

The first column is the stamped jet size.
Second column is the wire gauge drill bit size
Third is in mils and the fourth is in millimeters (for our Asian and European colleagues).



Regards
RSH

[dannomanno]

Thank You!!!!! I am a machinist in training and I was lookin for this exact thing. Thank you again!

[skuttadawg]

Why bother to go through the headache when jets are only a few bucks . Thats cheaper than the time you spend doing it and prevent you from having a " aw man " mistake and the jets should be smooth not course inside

[2wheelxtreme]

yea i agree dont bother with drilling it out to the size needed just pay 10 dollars or less to have a new one of the right size shipped to your home.

[super8504t]

Couldnt find a jet for my super 8, drilled it out (buddy did actually) and it runs SO much better. He said its easy to screw it up if you dont know what your doing though.

[dude]

Just to let you know some companies the jet # stamped on the jet is a different inside dia.
49ccscoot.com/printcomparison.html

[mainepeace]

Really? Interesting. How was that information collected? Just someone measuring a bunch of jets? I'd be curious to see if the reason there is a different number stamped is because it's more related to FLOW rather than actual hole size. The jets are pretty simple, but I'm sure there are minor variations in the jet design which all affect fuel flow. It would be an interesting experiment to swap out jets from different manufacturers to see how they relate to each other.

Greg

[rscotth]

The main reason I posted was for convenience. I happened to have a bunch of jets from my old RD and RZ but if I didn't I would wait two days to a week for them to be delivered to my door.

I am a mechanical engineer that specializes in gas turbine power plant maintenance so drilling a jet is absolutely no problem for me to execute.

Carb jets 101- Carburetor jet sizes are measured in hundredths of a millimeter not flow. For example, a 107 jet has an opening that is 1.07 mm in diameter and a 120 jet has a size of 1.20 mm.
Regards
RSH

[dude]

I am guilty of drilling jets. But a drilled jet flows different then a non drilled jet.

[2wheels4ever]

So; an altered hole in a little brass screw will throw the fuel supply, float mechanism, atomizer, throat venturi, all the way down the path and out the exhaust and thereforth the universe, into a state of irreversible catastrophe? Sigh. The tradeoffs of fattening up a F/A mixture

[mainepeace]

IF you have a way of properly drilling the hole then it should be fine. Vice grips and a handheld power drill is NOT the proper way. You'll end up making the hole wider than necessary and you WILL alter the flow characteristics. If you look into a jet you will see it's not just a simple hole. It is flanged and has a certain shape to it that has been designed for specific flow characteristics.

Greg

[rscotth]

Your right about jets being tapered. I did a little research and found this link: www.doghouserepair.com/store/item/3018/

Cool kit and a specific jet gauge measuring tool is also available.

I have also spoken to a few people that have drilled out jets on small engines for years with great success. I wouldn't do it on my supercharged Cobra but my scooter- probably.

RSH

[lbo]

Nice chart, thanks for posting it.

I have drilled my main out 2X, once when I added a tuned pipe and just recently when I modded my intake. Actually had my scooter dealer do it (they have a set of these bits), they have hand held "pin vise' that the jet would just twist down to open up or drill out bigger. The chart is a good reference.

[scooterman150]

I have a TGB303RS That I upgraded to a 72cc and had to modify the jet several times in order to achieve the best performance. Unfortunately I was unable to use different size jets at random because they were to hard to find at the time. What I did was start off with a larger bore to the jet.
The down fall was that I could not go smaller after drilling. Dumb, but it could save your engine from seizing due to being to lean. My trick to re drilling the jet to a smaller size was a simple idea. I soldered the jet closed with a typical electronic soldering gun and re drilled down to the next size. Solder sticks well to brass. I did this 3 times with the one jet and finally got that baby running sweet at 50 MPH. Yes it was time consuming but well worth it.
Check out this page I posted about it. www.drxmedia.com/drxsoftware/303RS/TGB303RS.htm
Click on the carb mod link..

good luck!

[timelancer]

I actually have ran drilled jets in all five of the Gy6 engines I have owned. MY 82cc required a jet mulitiple sizes larger than a #95 main, which to my knowledge is the largest they make for a 50cc stock carb. My current 90cc build is running a 125cc carb and I couldn't get a jet smaller than a 105, stock in the carb was a 110 and running both of them was spewing fuel all across the road. I filled one of my 105's with solder and drilled away until i got the right size. I'm sure they flow differently, but hey they don't make em for me so I build em

[trex90]

I wouldn't drill the jet. I do my own but I use reamers. Much better finish

[timelancer]

that actually doesn't sound like a bad method either, next time i'm in the woods for a different size jet i'll have to give that a try.

[carasdad]

Drilled many jets.....just know.....when you drill it to be a #85...according to drill bit size......it will come out larger....due to the 'slag' that builds up around the bit...making the hole bigger....you never know what you will end up with..... I found this out by using 'music' wire...to check hole size.......the #78 was actually an #84....and the #85 was actually a #90.... also you must have it aligned perfectly as you drill.....cause even slightly off center....and your orifice will become 'egg' shaped and not work properly..... Trust this old Native American 'Savage'.....and you shall see as well...

[carasdad]

Also must agree with Greg 'Mainepeace'.....jets are not measured by hole size......but by how much they flow. I have a friend who worked for Rousch racing...(Ford).....back in the day before EFI....they carried a small box of jets for their Holley carbs...because each track.....each elevation required something different....there is no 'Holy Grail' for jet size.......even engines of the same displacement.....will need a different jets.... btw Greg.....your site is looking great....good prices...and now a tech question link.....kick some azz bro.... heyachie a sumina deka laiiata tongo...<--our God does not gives us everything we want...only what we need to succeed.....and I think you will do well white skinned brother.......

[trex90]

Using cutting oil will help drills cut on size. Keeping it straight is another problem. Can be hard unless u have access to a lathe.