Tools you'll need:
- Jet gauges
- Jet reamers
- Pin vise to hold reamers (mine came with the reamers)
- Dial calipers (to measure the reamers)
- Electronics "helping hand" or bench vise
- Soldering gun/iron (I prefer the Weller on-demand guns as opposed to constant hot irons)
- Solder (not sure if it matters what kind, I just use the same as I do for electronics)
- Flat, fine file
- Welding gloves (to handle the hot jet if you need)
- Carb cleaner
- Sewing needle and string
First off, clean the jet you're going to resize. The carb cleaner and some needle and thread work great for getting rid of any varnish in the jet. I don't know if this matters, but it can't hurt when considering the solder needs to "bond" with the brass.
Next, gauge the jet so you know what you're working with! Many are not sized as marked. Here's what I started with...marked a 115, it's really about a 140.
Assuming you want to downsize the jet, you'll need to solder the hole partially closed. Obviously if you want to upsize, you can skip the whole soldering part and simply ream. When soldering, make sure you heat the jet and don't melt the solder and try to dribble it in the hole. It won't stick. Hold everything about like this, that's the tip of the soldering gun on the right:
Once you feel it's melted into the hole nicely, let it cool just a bit and then heat and melt it from the other side of the jet to make sure all sides are sticking nicely. It will look something like this when done:
Next, file the solder flat with the jet. If you didn't get enough heat throughout, you'll end up with ugliness:
I reheated and refiled and when the surface looked flawless I was happy.
Now it's time to ream! I like to use a reamer slightly larger than the hole I want. The thicker ones are easier to use as they don't wobble as much. You'll have to use the dial calipers to find the size reamer you need. I was after a 115 (1.15 mm) jet, so I picked a reamer that measured 1.20 mm.
Try and get the reamer as near center and straight on as you can. I don't think perfection is necessary, but I like my work to be neat. Be gentle when reaming. Some of the reamers are very thin and bend and wobble quite a bit when any downward pressure is applied. This will lead to crooked and wallowed holes, something you don't want!
Ream a bit, measure the hole, ream a bit more until you get the size you want. At this point I like to see how far in the reamer went before the hole went through. I figure if I get about 5 mm of solder lengthwise inside the jet, that's enough. If not, I'll start over.
When you're there, file the surface down flat and ream again to get a nice, smooth opening. I like to use one of the large reams to then slightly chamfer the edge of the hole.
After you're done, clean the jet thoroughly! Compressed air (your mouth), carb cleaner, and the needle and thread again will help get any bits of solder or brass out of there. No sense running that junk through your engine.
If your jet was marked, now's a good time to remove the marks (unless they are now correct). A dremel is good for that. It's nice to remark them with an awl or something similar, but a handy storage/organizer case and the gauges work also.
That's really about it. If your carb is hard to find jets for, this is the ticket. Good luck. Hopefully this helps, let me know if you have any questions or suggestions.
Kyle
