Jet drills are tiny drill bits used for cleaning, drilling, and measuring jets. They have numbered sizes. #80 is smallest and #60 is largest.
Useful for sizing to tell how big a jet really is (sometimes they’re drilled out or labeled wrong).
Useful for cleaning varnish or corrosion coating the inside of an old jet. It doesn’t really clean out any other way. The drill is used as a file, held with a needlenose pliers.
Useful for drilling jets to make a new size, as an alternative to buying ones. The drill is held with a needlenose pliers, and the jet is rotated with your fingers, with a drop of oil. To go down in size, fill the hole with solder and re-drill it smaller.
How small are moped jet holes? Moped main jets range from 0.018″ to 0.026″ (18 to 26 thousandths of an inch). Moped idle jets, like Tomos A55, are 0.011″ (11 thousandths of an inch). An average human hair is 0.003″ (three thousandths of an inch). So moped jet holes are 4 to 9 hairs wide!
1. A Tomos A55 idle jet (M4 thread) is physically bigger than a Puch Maxi main jet (M3.5 thread), but the hole size is much smaller. The photo shows how the #25 jet, 0.011″ (eleven thousandths of an inch), will allow the thinner wire of the wire wheel to pass through the hole, but not the thicker wire of the wire brush. This is a useful cleaning technique.
2. Shaun’s well used drill container from 1987
1. Drill Set USA-made
2. Set 1 China-made, only 2 of 20 are correct
3. Jet Drills made in USA
4. Set 2 China-made, only 6 of 20 are correct
USA-made Drills: All through the late 1980’s and 1990’s, Shaun (at Royal Cyclery and later at Myrons Mopeds) used the USA-made jet drills to service carburetors. The drill sizes are an American wire gauge. They did not vary in size. Those 20-piece Drill Sets 61 to 80, cost $40 in 2015, $33 in 1998. and $29 in 1987. Some are in clear plastic round dome containers, and some are in conventional metal drill set boxes.
China-made Drills: In the 2000’s there were many China made tools sold in “surplus” tool stores. The China made 20-piece Drill Sets 61 to 80, sell for $7 to $10, or one fourth as much. They have an excellent blue plastic container, that only lets out one at a time. But the drill sizes are all wrong. From about 2010 to 2014, Myrons Mopeds sold these inexpensive drill sets, not knowing that the drill sizes were inexact, to say the least.
So although the China sets cost one forth as much, they only have about seven or eight different sizes, and they lack the smaller sizes below 0.4 (or sometimes 0.6) mm. Each set is different.
Some have poorly made drills, twisted funny, bigger at the cutting end, or lumpy, varying in thickness. Some have poorly made cutting tips, so they might wander, grab and break, or not cut well.
Despite the poor quality and inexactness, the inexpensive drills are still useful for cleaning purposes, but not for measuring and maybe not for drilling. Fortunately, brass carburetor jets are the easiest thing to drill, with a drop of oil and a pilot hole already there.
Micro Drills and Wires for Sale Individually
Drills are measured at the shank. The cutting edge is 1 or 2% bigger.
Wires are steel guitar strings, cut into 5 inch lengths.
“Metric” jets say hundredths of a millimeter, so a 64 jet is 0.64 mm.
Dellorto and Bing aftermarket jets are “Metric” jets.
inch mm/# price what jets it cleans
inch mm/# price 00 Dellorto 000 Bing 000 Metric 000 Gurtner
0.011 wire none Gurtner Motobecane diffuser – two idle holes (.013)
0.0135 80 0 $6.00
0.0145 79 0 $5.00
0.0157 0.40 $3.00 38 (.0162) 42 (.0162)
0.0160 78 0 $4.00 40 (.0168) 44 (.0167)
0.0170 wire $0.50 42 (.0177) 46 (.0175)
0.0180 77 0 $3.50 44 (.0186) 50 (.0188)
0.0190 000 $2.00 46 (.0194) 52 (.0194)
0.0197 0.50 $2.00 48 (.0202) 54 (.0200) 51 (.0201)
0.0200 76 0 $3.50 49 (.0207) 56 (.0206) 00 (.0000) 210=52 (.0210)
0.0210 75 0 $4.00 51 (.0215) 58 (.0213) 00 (.0000) 220=54 (.0220)
0.0225 74 0 $5.00 55 (.0231) 62 (.0229) 00 (.0000) 230=56 (.0230)
0.0230 000 $2.00 56 (.0235) 64 (.0234) 00 (.0000) 240=58 (.0236)
0.0235 0.60 $2.00 58 (.0242) 66 (.0239) 00 (.0000) 245=59 (.0239)
0.0235 0.60 $1.50 58 (.0242) 66 (.0239) 00 (.0000) 250=60 (.0242)
0.0240 73 0 $3.00 60 (.0247) 68 (.0248) 63 (.0248)
0.0250 72 0 $3.50 62 (.0255) 70 (.0254) 65 (.0256)
0.0260 71 0 $4.50 66 (.0268) 74 (.0267) 68 (.0268)
0.0275 0.70 none 70 (.0280) 78 (.0280) 71 (.0280)
0.0280 70 0 $4.00 72 (.0287) 80 (.0287) 73 (.0287)
0.0292 69 0 $4.50 78 (.0306) 84 (.0301) 77 (.0303)
0.0300 wire none 80 (.0312) 00 (.0000) 79 (.0311) K80 (.0311)
0.0310 68 0 $4.50 82 (.0318) 00 (.0000) 81 (.0319)
0.0315 0.80 $2.00 84 (.0324) 00 (.0000) 82 (.0323)
0.0320 67 0 $3.00 86 (.0331) 00 (.0000) 84 (.0331)
0.0325 000 $2.00 88 (.0337) 00 (.0000) 86 (.0339)
0.0330 66 0 $4.50 90 (.0343) 00 (.0000) 88 (.0346)
0.0340 wire none 00 (.0000) 00 (.0000) 90 (.0354)
0.0350 65 0 $3.00 00 (.0000) 00 (.0000) 92 (.0362)
0.035 65 0 $3.00 MB (side mount) diffuser (.0358)
0.0354 0.90 $2.00 00 (.0000) 00 (.0000) 94 (.0370)
0.0360 64 0 $3.00
0.0370 63 0 $2.50
0.0380 62 0 $1.50
0.0390 61 0 $1.50
0.0394 1.00 $1.00
Tools for Cleaning Jets
1. Myron’s deluxe drill set, Price none, sorry no more.
2. Pin vise, a mini drill chuck, price $8.
3. Guitar string 0.017″
Guitar Steel Strings in the smaller sizes are excellent tools for cleaning small holes. Here is a 0.0170 inch steel wire guitar string, perfect for cleaning out a 1974-85 Tomos stock jet size 46 that has a 0.0175 inch hole. A Honda Express NC50 (Keihin) carburetor, has a long brass idle jet tube with a tiny jet hole at the far end, too far for a drill to reach. For that, only a 2 or 3 inch piece of 0.010″ steel guitar string will reach to clean it. Ultrasonic cleaners, carb spray, or soaking are not effective for that. Other examples are a Sachs 52 jet 0.0190 would be cleaned by a 0.018″ wire, or a Motobecane 230 jet 0.023″ would be cleaned by a 0.022″ wire. The wire has to be a little smaller than the hole. Plain steel strings range from 0.008″ to 0.017″ in steps of 0.001″. Wound strings range from 0.017″ to 0.065″.
1. Using a Micrometer to measure a 0.017″ wire
2. Torch Tip Cleaner Set
3. Root Canal Files
Welding Torch Tip Cleaners are another excellent tool for cleaning small holes. The tip has a cutting surface but not the sides. So it is made to clean the hole without widening it.
Wire Feeler Gauge Sets: There are also wire gauge measuring sets that look the same as the torch cleaner set shown.
Dentist’s Root Canal Files are also good for cleaning small holes. Color coded files range from 0.06 to 1.10 mm (0.0024 to 0.0433 inch).