Above, 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.
This will help you visualize how small these drills and jets are!
Moped main jets range from 0.018″ (#77 drill) to 0.026″ (#71 drill).
Moped idle jets, like Tomos A55, are 0.011″ (smaller than #80).
An average human hair is 0.003″ (three thousandths of an inch).
So moped jet holes are 4 to 9 hairs wide!
Shaun’s well used drill container from 1987
Jet 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.
Drill Set USA-made
Set 1 China-made
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.
Jet Drills made in USA
Set 2 China-made
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
These drills are measured at the shank (the smooth part). At the cutting edge they are 1 or 2% bigger.
These wires are steel guitar strings, cut into 5 inch lengths.
“Metric” jets have a number that literally means hundredths of a millimeter, so a 64 jet is 0.64 mm.
inch mm/# price moped jets that it cleans
0.011 wire N/A Gurtner Motobecane diffuser – two idle holes (.013)
0.0135 #80 $6.00
0.0145 #79 $5.00
0.0157 0.40 $3.00 Dellorto 38 (.0162), Bing 42 (.0162)
0.016 #78 $4.00 Dellorto 40 (.0168), Bing 44 (.0167)
0.017 wire $0.50 Dellorto 42 (.0177), Bing 46 (.0175)
0.018 #77 $3.50 Dellorto 44 (.0186), Bing 50 (.0188)
0.019 —— $2.00 Dellorto 46 (.0194), Bing 52 (.0194)
0.0197 0.50 $2.00 Dellorto 48 (.0202), Bing 54 (.0200), “Metric” 51 (.0201)
0.0200 #76 $3.50 Dellorto 49 (.0207), Bing 56 (.0206), Gurtner 210=52 (.0210)
0.021 #75 $4.00 Dellorto 51 (.0215), Bing 58 (.0213), Gurtner 220=54 (.0220)
0.0225 #74 $5.00 Dellorto 55 (.0231), Bing 62 (.0229), Gurtner 230=56 (.0230)
0.023 —— $2.00 Dellorto 56 (.0235), Bing 64 (.0234), Gurtner 240=58 (.0236)
0.0235 0.60 $2.00 Dellorto 58 (.0242), Bing 66 (.0239), Gurtner 245=59 (.0239)
0.0235 0.60 $1.50 Dellorto 58 (.0242), Bing 66 (.0239), Gurtner 250=60 (.0242)
0.024 #73 $3.00 Dellorto 60 (.0247), Bing 68 (.0248), “Metric” 63 (.0248)
0.025 #72 $3.50 Dellorto 62 (.0255), Bing 70 (.0254), “Metric” 65 (.0256)
0.026 #71 $4.50 Dellorto 66 (.0268), Bing 74 (.0267), “Metric” 68 (.0268)
0.0275 0.70 x N/A Dellorto 70 (.0280), Bing 78 (.0280), “Metric” 71 (.0280)
0.028 #70 $4.00 Dellorto 72 (.0287), Bing 80 (.0287), “Metric” 73 (.0287)
0.0292 #69 $4.50 Dellorto 78 (.0306), Bing 84 (.0301), “Metric” 77 (.0303)
0.030 wire N/A Dellorto 80 (.0312), “Metric” 79 (.0311), Gurtner K80 (.0311)
0.031 #68 $4.50 Dellorto 82 (.0318), “Metric” 81 (.0319)
0.0315 0.80 $2.00 Dellorto 84 (.0324), “Metric” 82 (.0323)
0.032 #67 $3.00 Dellorto 86 (.0331), “Metric” 84 (.0331)
0.0325 —— $2.00 Dellorto 88 (.0337), “Metric” 86 (.0339)
0.033 #66 $4.50 Dellorto 90 (.0343), “Metric” 88 (.0346)
0.034 wire N/A “Metric” 90 (.0354)
0.035 #65 $3.00 “Metric” 92 (.0362), Gurtner MB (side mount) diffuser (.0358)
0.0354 0.90 $2.00 “Metric” 94 (.0370)
0.036 #64 $3.00
0.037 #63 $2.50
0.038 #62 $1.50
0.039 #61 $1.50
0.0394 1.00 $1.00
Deluxe 40-piece Micro Drill Set
Myron’s Mopeds two case deluxe micro drill set, 80 to 72 (small) and 71 to 60 (large) plus many in-between sizes.
Price none, sorry no more.
Slide clear top plastic until hole is over drill (and pointer is on desired drill number). Only lets one drill out at a time. Never take out more than one at a time, or they can get mixed. The case keeps them organized. If any get lost, dull, or broken, individual drills can be bought at some hardware stores for $3-$4 each.
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.
Here is a pin vise, a mini drill chuck, price $8
Other Tools for Cleaning Jets
Using a micrometer to measure a 0.017″ wire
Guitar string
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″.
Torch Tip Cleaner Set
Root Canal Files (say ahhh)
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).