Trying to sort out my bogging down/hesitation problem in mid-range RPM or WOT conditions so I took the carbs apart yesterday and to my surprise, I have size 102 main jets, size 35 pilots. So the pilots are stock but what's up with size 102 mains when OEM size is 105 and the engine was previously overbored?

Can anyone see the logic?

 

race gas could be one reason

 

can't imagine why you would want to have a lean condition on a overbored engine. not even the use of race gas could explain that.

even if you left the engine stock and put a more open exhaust, you would still need to jet higher.

running jets lower than stock is a new one to me.

 

It's -possible- that they're DJ 102 jets or something of the sort; I think there's a chart somewhere that (supposedly) shows the size comparisons between regular Keihin jet sizes and DJ sizes. Maybe someone a long time ago put on a DJ kit, no pipe, no airbox mod, and used the DJ 102s to get about the same "effect" as the regular (stock) 105 jet.

But that's a lot of "if" crap. Since you're there, if you have some bigger jets, toss 'em in there and see what happens.

 

well even with the 102's in there race gas could be possible. you can run less fuel in a motor with race gas hense why the smaller jets.

 

Did some more investigating and I think even the 102's are stock. Looking through the parts on fiche finders, I found this:

24 JET, MAIN (#102) 99101-GHB-1020 (replaces 99101-393-1020)
24 JET, MAIN (#105) 99101-GHB-1050 (replaces 99101-393-1050)


...which tells me that some bikes may have come with 102's while others with 105's.

I don't have bigger jets on hand otherwise I would have thrown them in there and tested but I think I'll have to anyway. Now question: can I just change the main jets and nothing else? In other words, is it possible to just get a set of main jets without having to buy a whole kit (pilots, needles, etc) and what repercussions would it have?

Also, I might be looking for a way to create more restriction in the exhaust/pipe, mainly to dampen the sound a little (now I understand why ppl complain about the friggin loud D&D pipes). If I go this route, would it eliminate the need for larger jets?

Thanks for the input

 

Yes there is a difference in flow rates between Dynojet and Keihin. here is the chart, (hopefully it works)

Width------Kehein # -- 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

Also here are the Dynojet kits for the 87-89 and the 90 models. They deteail the jets that are supplied.

www.dynojet.com/pdf/1122.pdf
www.dynojet.com/pdf/1135.pdf

 

Main jet was 102 on UK models with KeihinVG22A carbs, and was 105 onVG20A (California) and VG21A (other US states) carbs, according to some specs I've seen.

 

hey


my bike was doing the same thing whin i mid range rpm, what i did was get4 hotter plug's and run it it, does way better burns the gas better too mine was jetted and i dident know itwhin i bought the bike