JETS-R-US: ORIFICE SIZE, CARB SWAPPING CONVERSION
AND
CONVERSION FOR KEIHIN TO MIKUNI TO DYNOJET
This chart is a rough approximation, it is an aid to conversion. There is no way to accurately match flow rates between different manufacturers.
Question, I am swapping a Keihin carb for a Mikuni carb, what jet do I use? The table below may give a place to start. For example lets suppose that a Mikuni carburetor has a size 100 main jet in it, the equivalent Keihin jet would be a 110. After the carb swap to a keihin carb start with keihin 110 jet. The chart will not be a perfect match because there are many variables, for example, different carb flow characteristics, different needles, orifices etc. but it is a starting point.
Question, I have some dynojets and would like to purchase Jets R Us jets, how do I compare the sizes? Dynojet does not produce numerically matched jets. Because dynojets are not manufactured 100% the same as mikuni and keihin there is not an exact comparison between the two, flow rate will be different.
Note that Keihin jets cannot be placed in Mikuni carbs and vice versa.
The table below is an approximation, results in the carburetor will vary, due to fluid dynamics these will not be exact equivalent flow rates.
| Diameter | Keihin | Dynojet | Mikuni (uses tapered holes to achieve flow rate, table below not accurate) |
|---|---|---|---|
| .025 | 70 | 74 | 70 |
| .026 | 72 | 76 | |
| .027 | 75 | 78 | 72.5 |
| .029 | 78 | 80 | 75 |
| .030 | 80 | 82 | 77.5 |
| .031 | 82 | 84 | |
| .032 | 85 | 86 | 80 |
| .033 | 88 | 88 | 82.5 |
| .034 | 90 | 90 | 85 |
| .035 | 92 | 92 | |
| .036 | 95 | 94 | 87.5 |
| .037 | 98 | 96 | 90 |
| .038 | 100 | 98 | 92.5 |
| .039 | 102 | 100 | |
| .040 | 105 | 102 | 95 |
| .041 | 108 | 104 | 97.5 |
| .042 | 110 | 106 | 100 |
| .043 | 112 | 108 | |
| .044 | 115 | 110 | 102.5 |
| .045 | 118 | 112 | 105 |
| .046 | 120 | 114 | 107.5 |
| .047 | 122 | 116 | |
| .048 | 125 | 118 | 110 |
| .049 | 128 | 120 | 112.5 |
| .050 | 130 | 122 | 115 |
| .051 | 132 | 124 | |
| .052 | 135 | 126 | 117.5 |
| .053 | 138 | 128 | 120 |
| .054 | 140 | 130 | 122.5 |
| .055 | 142 | 132 | |
| .056 | 145 | 134 | 125 |
| .057 | 148 | 136 | 127.5 |
| .058 | 150 | 138 | 130 |
| .059 | 152 | 140 | |
| .060 | 155 | 142 | 132.5 |
| .061 | 158 | 144 | 135 |
| .062 | 160 | 146 | 137.5 |
| .063 | 162 | 148 | |
| .064 | 165 | 150 | 140 |
| .065 | 168 | 152 | 142.5 |
| .066 | 170 | 154 | 145 |
| .067 | 172 | 156 | |
| .068 | 175 | 158 | 147.5 |
| .069 | 178 | 160 | 150 |
| .070 | 180 | 162 | 152.5 |
| .071 | 182 | 164 | |
| .072 | 185 | 166 | 155 |
| .073 | 188 | 168 | 157.5 |
| .074 | 190 | 170 | 160 |
| .075 | 192 | 172 | |
| .076 | 195 | 174 | 162.5 |
| .077 | 198 | 176 | 165 |
| .078 | 200 | 178 | 167.5 |
| .079 | 202 | 180 | |
| .080 | 205 | 182 | 170 |
| .081 | 208 | 184 | 172.5 |
| .082 | 210 | 186 | 175 |
| .083 | 212 | 188 | |
| .084 | 215 | 190 | 177.5 |
| .085 | 218 | 192 | 180 |
| .086 | 220 | 194 | 182.5 |
| .087 | 222 | 196 | |
| .088 | 225 | 198 | 185 |
| .089 | 228 | 200 | 187.5 |