Dynojet - Mikuni - Keihin jet sizes conversion

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When you're jetting your carbs you will notice that the same size jets from different suppliers have different numbers. The following chart will give you an idea of which numbers are the same for the different companies. Remember, though, that this will only put you in the ballpark. Plenty of trial and error will be needed to get it right.

A note from Dynojet

  • We are often asked for a "cross reference" sheet that compares our main jets to Mikuni or Keihin. The fact is you cannot directly interchange the jets for a given size. Many things affect fuel flow through a jet of the same orifice size. The entry and exit tapers of our main jets differ from those of other companies. Due to this, the fuel flow changes as a function of velocity through the carburetor venturie. This means that two jets of equal orifice size will have a different fuel flow curve relative to intake air speed. At a certain speed the two may flow equally, but a change in velocity changes the flow characteristics. The Dynojet main jet hole size is measured in millimeters. For example, a DJ142 has a 1.42mm hole.
Michael Cory
Dynojet Research & Development

Available jets

You never know what kind of jets you might find at your local shop when you try to find new jets. Wes says to just ask for jets that will fit in a Harley. That keeps the sales droid from having to think too much. Asking about Ninja 250s causes all sorts of confusion. Having this chart, and knowing what will fit and how they compare to each other, will help you figure out if they have what you can use.

There are four current sources of main jets which will fit the Ninja 250:

1) Keihin - OEM main jets - Jets are measured using an unknown convention in steps of 2 or 3. Available from Kawasaki dealers 2 sizes larger and 2 smaller than the Ninja 250's stock #105 main jets.

2) Dynojet - Measured in mm. Dynojet numbers are simply the hole diameter. A 140DJ main has a 1.40mm (0.055") diameter hole in it at the threaded end. Available in .02mm increments. Marked with a 'DJ' on the jet.

3) Precision Engineering - Also sold under the names 'RD Precision Engineering' and 'Freeman Automotive' - All are marked with an 'AB' on the jet. Like Dynojet, measured in mm, but come in .025mm increments.

4) Mikuni - Made for Mikuni Carburetors, but will also fit Keihin. Available in 2.5 increments. Mikuni uses yet another measurement convention - reportedly based on flow rate. The result is that Mikuni's sizes are vastly different from the other makers'.

The different manufacturers' jets will have a slightly different taper to the orifice, which can affect flow. This means that there will most likely be very slight differences between the same diameter jets from different makers.

The measurements in this chart are from the actual measured orifice size, in millimeters. Keihin 105 is the stock main jet.


unknown = Not yet measured
n/a = This size not available from this manufacturer

Measured mm Keihin Dynojet Precision (AB) Mikuni

(unconfirmed)

Flow

(cc/second)

.94 unknown DJ094 n/a 87.5 2.19
.95 n/a n/a AB95 n/a 2.24
.96 unknown DJ096 n/a 90 2.29
.975 n/a n/a AB97.5 n/a 2.36
.98 100 DJ098 n/a n/a 2.38
1.00 102 DJ100 AB100 92.5 2.48
1.02 105 (stock) DJ102 n/a 95 2.58
1.025 n/a n/a AB102.5 n/a 2.61
1.04 108 DJ104 n/a 97.5 2.69
1.05 n/a n/a AB105 n/a 2.74
1.06 110 DJ106 n/a 100 2.79
1.075 n/a n/a AB107.5 n/a 2.87
1.08 unknown DJ108 n/a n/a 2.90
1.10 unknown DJ110 AB110 102.5 3.02
1.12 unknown DJ112 n/a 105 3.13
1.125 n/a n/a AB112.5 n/a 3.16
1.14 unknown DJ114 n/a 107.5 3.25


Again, the chart is fine to use to get you in the ballpark. However, once you start zeroing in on the correct jetting specs, you should be basing your jetting changes based on what the bike is telling you--not what someone else (who isn't testing with you) says is right for your bike/situation. There aren't really any shortcuts to getting jetting right.

Read the rest of the information in the jetting section of the FAQ, then get out there and do some testing.

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