Don't know if its true, but heard a 120 Dynojet is equivalent to a 122 Keihan.
Anyone out there confirm this or tell me exactly what the difference is between Dynojet and Keihan jets?

I found this on the net a while ago, not sure how accurate it is though:

Main Jet Equivalents:

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

DJ dynojet main jets are longer that a stock Keihin main jets. Bore size to bore size this means a dynojet jet will always be richer. There are two types of dynojet jet tho, the DJ and CJ. The CJ is much shorter and is closer to a Keihin Jet. DJ jets are the most common type of dynojet tho.

I'd try to always use genuine Keihin jets, they're better made and more relevant when comparing to stock jetting figures.

How do they differ aesthetically?

I just pulled mine out and they are 125 all round. They are round with a flat screwdriver slot in the top, have a groove on the external side running all the way around, the number 125 stamped on the top but no keihin star logo anywhere?

The primarys have the number and the Keihin star stamped on them, so that is a no brainer.

But I am curious about the mains??

Thread revival coming up...

RVF wrote:DJ dynojet main jets are longer that a stock Keihin main jets. Bore size to bore size this means a dynojet jet will always be richer. There are two types of dynojet jet tho, the DJ and CJ. The CJ is much shorter and is closer to a Keihin Jet. DJ jets are the most common type of dynojet tho.

I'd try to always use genuine Keihin jets, they're better made and more relevant when comparing to stock jetting figures.

If RVF is still active, could he explain what the bit in bold means, or could anyone else? Does it mean that if I want to try 118K jets, then although 112DJ is listed here as equivalent hole size, I should start by trying 110DJ? I ask because my friendly local DJ centre keeps, you guessed it, DJ jets in stock. We have already had a little misunderstanding where they sold me a set of 120DJ jets, which turn out to be equivalent to 128K and if this comment above means what I think it does, maybe they're even richer than that.

999Gomerz wrote:How do they differ aesthetically?

The DJ main jets have a thicker/higher head, and just the number is stamped on the top. Keihin jets have a shorter/thinner head, and the number is stamped on the side along with a star logo.

Some manufacturers calibrate the jet in cc/min and others just quote a diameter in mm so you need to use like for like. I had the problem when i went from a DJ main to a Mikuni and the dyno guy thought i was nuts cause the bike was mega rich, ended up with the same size jet (number) but the new was about 10 bigger than the old.

Little sleepy on this one but since the DJ jets are longer they sit closer to the fuel?

Perhaps this has an effect too?

Failling to see exactly how at the moment.

Always chucked DJ jets though, Kehin can be had cheap and everybody knows where they stand.

Neosophist wrote:Little sleepy on this one but since the DJ jets are longer they sit closer to the fuel?

Perhaps this has an effect too?

Failling to see exactly how at the moment.

Always chucked DJ jets though, Kehin can be had cheap and everybody knows where they stand.

I can't work it out either.

I would rather work with K jets, but since my dyno centre only stock DJ jets, I am pretty well stuck. They have offered to exchange jets which are no good, so it's not worth me buying K jets which are non-returnable, when they will offer to exchange for me.

Fair enough... then can't you just take the bike down there and do a few runs, it shouldn't take more than 3 or 4 runs to get the best mains?

I've done a bit of looking around on some of the forums I use.

I found a quote from Zimm on zxrworld whose really quite knowledgable with 400's/

DJ jets are longer, so sit lower in the float bowls. This can mean needing a slightly diff float height compared to keihin jets... dont know which is "better" per se... part throttle at under 5k isnt really relevant on a tuned 400

A quote from DJ themselves, although how much of this is marketing 'hype' and how much of it really happens I don't know, and dont' have the jets nor equipment to verify.

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

I seem to recall dynojet jets needing the dynojet needles too in order to 'flow' at their best. Never had good results with either though, but people have so it's not impossible, especially if you have a dynocentre full of them! :)

Perhaps start with one size down from what you would buy from Kehin and go from there?

Interesting thread........

Going from the recommendations on this site, I changed the original 110 mains for RO 115/118 - all other settings are stock.
Ever since, the bike rides great but I have a feeling that it's a bit rich. A dyno run will tell.

If it is a bit rich do I go for 115/118 Keihin or go for smaller RO jets (are they dyno jets?
It is surprising how rejetted bikes on here run hideously rich......

Phil