Keihin vs Mikuni

[RIDE-RED 250r]

Can someone tell me if jetting sizes are universal/standard between the brands or do they each have their own size scale? Just wondering after discussing jetting with a friend about jet sizes in my R and his ds650. My R has settled on a 195 main with the bolt ons i have and his DS650 is running i think a 170. But as you know, my R has a Keihin and the DS runs a Mikuni. I was just wondering if the jet sizes are on the same scale or not. Thanks

[4cylinders]

hey, no, they both are sizes. not actual hole size, just a number.

[RIDE-RED 250r]

Ok, so you are saying the 2 brands have a different jet sizing scale? In other words a Keihin #195 isnt the same size as a Mikuni #195?

[4cylinders]

hey, correct.

[NOS_350X]

different brands different jets

[CoeShow]

Keihin jets are actually numbered as to their size. I believe Mikuni uses a "flow" method for their numbering system. In any event, your 195 main jet is actually 1.95mm. There is NO relation to size between Keihin and Mikuni jet numbers. They are completely different and non interchangeable as well.

[MonroeMike]

http://planetminis.com/community/topic/50970-finally-found-the-true-diameter-of-jets/

(Width = true hole diameter)
Width------Keihin # -- DynoJets # -- Mikuni #
0.0350---- 92.5--------- 92---------- 86.3
0.0360---- 95----------- 94---------- 88.1
0.0370---- 97.5--------- 96---------- 90.0
0.0380---- 100---------- 98---------- 91.9
0.0390---- 102.5------- 100---------- 93.8
0.0400---- 105--------- 102---------- 95.6
0.0410---- 107.5------- 104---------- 97.5
0.0420---- 110--------- 106---------- 99.4
0.0430---- 112.5------- 108--------- 101.3
0.0440---- 115--------- 110--------- 103.1
0.0450---- 117.5------- 112--------- 105.0
0.0460---- 120--------- 114--------- 106.9
0.0470---- 122.5------- 116--------- 108.8
0.0480---- 125--------- 118--------- 110.6
0.0490---- 127.5------- 120--------- 112.5
0.0500---- 130--------- 122--------- 114.4
0.0510---- 132.5------- 124--------- 116.3
0.0520---- 135--------- 126--------- 118.1
0.0530---- 137.5------- 128--------- 120.0
0.0540---- 140--------- 130--------- 121.9
0.0550---- 142.5------- 132--------- 123.8
0.0560---- 145--------- 134--------- 125.6
0.0570---- 147.5------- 136--------- 127.5
0.0580---- 150--------- 138--------- 129.4
0.0590---- 152.5------- 140--------- 131.3
0.0600---- 155--------- 142--------- 133.1
0.0610---- 157.5------- 144--------- 135.0
0.0620---- 160--------- 146--------- 136.9
0.0630---- 162.5------- 148--------- 138.8
0.0640---- 165--------- 150--------- 140.6
0.0650---- 167.5------- 152--------- 142.5
0.0660---- 170--------- 154--------- 144.4
0.0670---- 172.5------- 156--------- 146.3
0.0680---- 175--------- 158--------- 148.1
0.0690---- 177.5------- 160--------- 150.0
0.0700---- 180--------- 162--------- 151.9
0.0710---- 182.5------- 164--------- 153.8
0.0720---- 185--------- 166--------- 155.6
0.0730---- 187.5------- 168--------- 157.5
0.0740---- 190--------- 170--------- 159.4
0.0750---- 192.5------- 172--------- 161.3
0.0760---- 195--------- 174--------- 163.1
0.0770---- 197.5------- 176--------- 165.0
0.0780---- 200--------- 178--------- 166.9
0.0790---- 202.5------- 180--------- 168.8
0.0800---- 205--------- 182--------- 170.6
0.0810---- 207.5------- 184--------- 172.5
0.0820---- 210--------- 186--------- 174.4
0.0830---- 212.5------- 188--------- 176.3
0.0840---- 215--------- 190--------- 178.1
0.0850---- 217.5------- 192--------- 180.0
0.0860---- 220--------- 194--------- 181.9
0.0870---- 222.5------- 196--------- 183.7
0.0880---- 225--------- 198--------- 185.6
0.0890---- 227.5------- 200--------- 187.5



Keep this in mind---> From a Dynojet tech rep:

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 venture. 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
Research & Development
Phone: 800-992-4993 EXT. xxx
Michael@Dynojet

[Dirtcrasher]

Nice link Mike!!

[RubberSalt]

They are very different. Keihin is a longer jet and Mikuni is a shorter jet. As 3WW said, mikuni measure with a flow rate, the amount of fuel that jet can give out in a minute in milliliters. As that web site states, its retarded because a bunch of stuff determines the flow rate. Dynojet and keihin are smarter about it, they use the size of the hole as the jet number. Easier to drill a jet up when jetting. Also, i strongly prefer keihin carbs over mikuni :-p

Wish i had me a 30-32mm keihin flat slide right about now.. lol

[RIDE-RED 250r]

Thanks everybody for the good info! Its something I have wondered about for quite some time. Wasnt looking to put Mikuni jets in a Keihin carb or vice-versa by any means! LOL!