Jet Drilling & OEM Honda Jet P/N's

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Wheelman-111
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Jet Drilling & OEM Honda Jet P/N's

Post by Wheelman-111 »

Jet Drilling Info

It's great to have a stockpile of jets lying around when tuning a carburetor, but not everyone wants to spend that kind of money. Jet's range in price from roughly $2.50 up to about $10 and sometimes you'll try quite a few of them to get the tune right. You may also need different jetting for summer or winter termperatures and other variables. If you own or work on more than one type of scooter or ever swap carburetors, the jets you bought tning the first carburetor may not work and then you're stuck spending more money on jet kits. There is an option that can save you money, and save you from waiting on the mail carrier to drop off your new jets.

Many carburetor jets can be drilled to get you in proper tune. Don't just go out and grab any drill bit that looks small enough to you. You'll need to get a selection of proper bits, most likely numbered drill bits. Here are a couple of links to affordable drill bits suitable for drilling jets.

Drill Bit City

Harbor Freight Tools

The chart below shows drill bit sizes by number, fractional standard, and metric units converted into actual size and metric jet size. There are more fractional and metric drill bits available, but this should cover most needs for small carburetors.

Bit Size Inches Millimeters Jet Size
#80 0.0135 0.3429 34.29
#79 0.0145 0.3683 36.83
1/64" 0.015625 0.3969 39.69
#78 0 .016 0.4064 40.64
#77 0.018 0.4572 45.72
0.5mm 0.0197 0.5 50
#76 0.02 0.508 50.8
#75 0.021 0.5334 53.34
#74 0.0225 0.5715 57.15
#73 0.024 0.6096 60.96
#72 0.025 0.635 63.5
#71 0.026 0.6604 66.04
#70 0.028 0.7112 71.12
#69 0.0292 0.74168 74.168
0.75mm 0.0295 0.75 75
#68 0 .031 0.7874 78.74
1/32" 0.03125 0.7938 79.38
#67 0.032 0.8128 81.28
#66 0.033 0.8382 83.82
0.85mm 0.0335 0.85 85
#65 0.035 0.889 88.9
#64 0.036 0.9144 91.44
#63 0.037 0.9398 93.98
0.95mm 0.0374 0.95 95
#62 0.038 0.9652 96.52
#61 0.039 0.9906 99.06
1mm 0.0394 1.0 100
#60 0.04 1.016 101.6
#59 0.041 1.0414 104.14
#58 0.042 1.0668 106.68
#57 0.043 1.0922 109.22
1.1mm 0.0433 1.1 110
#56 0.0465 1.1811 118.11
3/64" 0. .046875 1.1906 119.06
1.25mm 0.0492 1.25 125
1.3mm 0.0512 1.3 130
#55 0.052 1.3208 132.08
#54 0.055 1.397 139.7
1.45mm 0.0571 1.45 145
1.5mm 0.0591 1.5 150
#53 0.0595 1.5113 151.13
1/16" 0.0625 1.5875 158.75
1.6mm 0.063 1.6 160
#52 0.0635 1.6129 161.29
#51 0.067 1.7018 170.18
1.75mm 0.0689 1.75 175
#50 0.07 1.778 177.8
#49 0.073 1.8542 185.42
#48 0.076 1.9304 193.04
5/64" 0.078125 1.9844 198.44
#47 0.0785 1.9939 199.39
2mm 0.0787 2.0 200
2.05mm 0.0807 2.05 205
#46 0.081 2.0574 205.74
#45 0.082 2.0828 208.28
#44 0.086 2.1844 218.44
#43 0.089 2.2606 226.06
#42 0.0935 2.3749 237.49
3/32" 0.09375 2.3813 238.13
#41 0.096 2.4384 243.84
#40 0.098 2.4892 248.92
2.5mm 0.0984 2.5 250
#39 0.0995 2.5273 252.73
#38 0.1015 2.5781 257.81
#37 0.104 2.6416 264.16
#36 0.1065 2.7051 270.51
7/64" 0.109375 2.7781 277.81
#35 0.11 2.794 279.4
#34 0.111 2.8194 281.94
#33 0.113 2.8702 287.02
2.9mm 0.1142 2.9 290
#32 0.116 2.9464 294.64
3mm 0.1181 3.0 300
#31 0.12 3.048 304.8
1/8" 0.125 3.175 317.5
#30 0.1285 3.2639 326.39
3.3mm 0.1299 3.3 330
#29 0.136 3.4544 345.44
3.5mm 0.1378 3.5 350
#28 0.1405 3.5687 356.87
9/64" 0.140625 3.5719 357.19
3.6mm 0.1417 3.6 360
#27 0.144 3.6576 365.76
3.7mm 0.1457 3.7 370
#26 0.147 3.7338 373.38
#25 0.1495 3.7973 379.73
#24 0.152 3.8608 386.08
#23 0.154 3.9116 391.16
5/32" 0.15625 3.9688 396.88
#22 0.157 3.9878 398.78
4mm 0.1575 4.0 400
#21 0.159 4.0386 403.86
#20 0.161 4.0894 408.94
4.2mm 0.1654 4.2 420
#19 0.166 4.2164 421.64
#18 0.1695 4.3053 430.53
11/64" 0.171875 4.3656 436.56
#17 0.173 4.3942 439.42
#16 0.177 4.4958 449.58
4.5mm 0.1772 4.5 450
#15 0.18 4.572 457.2
#14 0.182 4.6228 462.28
#13 0.185 4.699 469.9
3/16" 0.1875 4.7625 476.25
#12 0.189 4.8006 480.06
#11 0.191 4.8514 485.14
#10 0.1935 4.9149 491.49
#9 0.196 4.9784 497.84
5mm 0.1969 5.0 500
#8 0.199 5.0546 505.46
#7 0.201 5.1054 510.54
13/64" 0.203125 5.1594 515.94
#6 0.204 5.1816 518.16
#5 0.2055 5.2197 521.97
5.25mm 0.2067 5.25 525
#4 0.209 5.3086 530.86
#3 0.213 5.4102 541.02
5.5mm 0.2165 5.5 550
7/32" 0.21875 5.5563 555.63
#2 0.221 5.6134 561.34
#1 0.228 5.7912 579.12

That seems simple enough, but unfortunately it gets a little more complicated and confusing. Apparently different manufacturers use different rating methods for their jets. DynoJet is supposed to be the actual size of the jet (100 = 1.00mm), although the numbers on every chart I've seen are close to accurate there, but not 100% correct. Mikuni is said to use flow numbers rather than actual size for it's ratings (100 = 100cc per minute). I've been unable to find any good information on how Keihin determines it's jet sizes. Keihin jets have been very close to actual size from my experience.

The way a jet is made changes the amount of flow it is capable of as well. Meaning, a jet from one manufacturer that is tapered or chamfered in a different manner could flow more or less than another manufacturer's jet of the same diameter. For this reason, it is said that no exact comparisons can be made with this data. This chart is intended to get you on the right track, but may not be completely accurate.

CLICK HERE FOR A PRINTABLE VERSION OF THIS CHART.

Diameter (in) Mikuni DynoJet Keihin
0.035 86.3 92 92.5
0.036 88.1 94 95
0.037 90 96 97.5
0.038 91.9 98 100
0.039 93.8 100 102.5
0.040 95.6 102 105
0.041 97.5 104 107.5
0.042 99.4 106 110
0.043 101.3 108 112.5
0.044 103.1 110 115
0.045 105 112 117.5
0.046 106.9 114 120
0.047 108.8 116 122.5
0.048 110.6 118 125
0.049 112.5 120 127.5
0.050 114.4 122 130
0.051 116.3 124 132.5
0.052 118.1 126 135
0.053 120 128 137.5
0.054 121.9 130 140
0.055 123.8 132 142.5
0.056 125.6 134 145
0.057 127.5 136 147.5
0.058 129.4 138 150
0.059 131.3 140 152.5
0.060 133.1 142 155
0.061 135 144 157.5
0.062 136.9 146 160
0.063 138.8 148 162.5
0.064 140.6 150 165
0.065 142.5 152 167.5
0.066 144.4 154 170
0.067 146.3 156 172.5
0.068 148.1 158 175
0.069 150 160 177.5
0.070 151.9 162 180
0.071 153.8 164 182.5
0.072 155.6 166 185
0.073 157.5 168 187.5
0.074 159.4 170 190
0.075 161.3 172 192.5
0.076 163.1 174 195
0.077 165 176 197.5
0.078 166.9 178 200
0.079 168.8 180 202.5
0.080 170.6 182 205
0.081 172.5 184 207.5
0.082 174.4 186 210
0.083 176.3 188 212.5
0.084 178.1 190 215
0.085 180 192 217.5
0.086 181.9 194 220
0.087 183.7 196 222.5
0.088 185.6 198 225
0.089 187.5 200 227.5

Alright, so you've got your new drill bits and you're ready to start tuning, but how do you drill a jet? There are two pretty common methods used for drilling jets, hand drilling and using a drill press.

Hand drilling simply involves holding the drill bit in your hand and gently turning it to drill the jet. Hand drilling is pretty simple on most common brass carburetor jets, but may not work on jets made from harder materials. Don't try to force the drill though the jet. Spin it carefully and don't push it into the jet. Small drill bits are very fragile and break off easy. If you break a bit off inside of a jet, you may not be able to get it out, and even if you do you just broke the drill bit that you need.

If you wish to drill the jet with a drill press, you need a vice or clamp capable of holding the bit at a 90 degree angle from the jet. It is very important to drill straight in order to get an accurate jet size. If a jet is drilled at an angle or if the bit wobbles the jet will actually be larger than the size you are aiming for. Just as hand drilling, apply only gentle pressure. Let the drill bit work it's way through the jet to avoid breaking the bit.

If you go too far when drilling a jet, it is possible to go back to a smaller size. Brass jets can be heated with a torch and then solder can be used to fill the jet. Once the jet is filled, simply re-drill it to the size you want.

If possible, it is a good idea to keep a stock jet or two around just incase.

Submitted by OdinXXiX
Wheelman-111
Most of my money is spent on scooterparts. The rest is just wasted.
"ISO": '03 Vespa ET4 Malossi187 74MPH
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mousewheels
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Re: Jet Drilling Contributed by OdinXXIX

Post by mousewheels »

The table copied into this thread is available at this link and is easier to read.
http://www.49ccscoot.com/jetdrill.html

Info noted:
  • Keihin and Mikuni jet numbers do not map to orifice size in mm.
  • Keihin and Mikuni jets are calibrated differently, a 130 Keihin is sized like a 115 Mikuni
  • Mikuni has more than one jet numbering scheme
----- Hondaspree's table ----
To improve upon the external table these changes are made:
  • Corrected decimal/inch errors
  • Added a drill size column
Image


-- Related and Supporting info
1) Dynojet replacements are sized by orifice size (mm x 100). Thus a '92' DynoJet is 0.92mm.
* The Dynojet main jet hole size is measured in millimeters. For example, a DJ142 has a 1.42mm hole.

Michael Cory
Dynojet Research & Development
2) The Inch diameter column in the table posted at top of thread is not accurate. Diameter goes up *exactly* 0.001 inch for every 0.02mm.

Error: that is a rounded value. The decimal inch change for 0.02mm is 0.000787. Rounding created an accumulating error in the table.

3) Mikuni Jets: The Mikuni jet used in the TM series carb (4/042) is calibrated differently from other Mikuni jets. It does not line up with the Mikuni column in this thread. The link below gives conversion info to get to that carb's jet size.
http://www.ozebook.com/compendium/t500_files/mikuni.pdf
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Re: Jet Drilling & OEM Honda Jet P/N's

Post by mousewheels »

Bear45-70 has provided a list of factory jets for the Honda OEM carbs. The original table provides prices, about all were around $6 - $8 from his source.

Link to original thread viewtopic.php?f=3&t=14110


-- mousewheels << 05/27/2012>>
Members report fit issues with the -GHB jets. Only -GHB jet I can find which crosses to a PA carb is the 99112-068 jet.


--- << Bear45-70 writes>>

IMO, drilling jets is a poor practice at best. Jets are flow rated and not just a hole of a specific size. If you look at an unmolested jet it is chamfered (tapering into and out of the hole). Drilling destroys the smooth flow. Order jets form Honda or better yet one of the aftermarket guys.

Here is a list of the 99101-187-0XX0 jets available from Honda.
Honda_PA_Carb_Jets.GIF
Honda_PA_Carb_Jets.GIF (13.71 KiB) Viewed 19366 times
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