Jet Needles / Main Jets / Gas Mileage
- otakar
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74 Z1-A stock
76 KZ-900 Totaly stock vice MAC pipe
77 KZ-1000A stock
78 Z1-R 100%MINT 500 original Mi.
78 Z1-R Yoshi 1103 kit stage 1 cams Yoshi pipe. Etc
79 KZ-1300 (1400)
80 KZ-1300
81 Scratch built GPz1150R
82 KZ1000
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- bountyhunter
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1979 KZ-750 Twin
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- andy9802gt
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- If it tastes that good, eat it yourself.
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'78 KZ1075 LTD
stage 1 head by Larry Cavanaugh
race built crank by John Pearson
Mikuni rs34's
k410 cams
back cut tranny
8" over D&G swinger
proving once again that age and treachery is better than youth and enthusiasm
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- WABBMW
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- Let The Good Times Roll !
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The only thing that puzzles me, is that the gas mileage is still the same, at about 43 MPG, as it was with the 4 mm. shimming. I have made the same run at least 50 times, and can usually predict the mileage within 5 MPG. The way I was riding, it was averaging in the low 50s before with stock Main jets and jet needles in the original single clip position. And I was riding easy - not over 1/4 throttle. I am surprised that 1 mm. hurt the mileage that much. Maybe there is something else going on, but I don't have a clue what it might be. Any ideas out there?
Thanks for all the replies.
Bill Baker
Houston, Texas
1982 KZ650 CSR
2008 Yamaha FZ1
2006 Yamaha FZ1
1977 Honda Supersport 750 four (sold)
1984 Honda Nighthawk 650 (sold)
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- larrycavan
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I changed the shims under the jet needles from 4 mm. richer than stock, down to 1mm. richer. The bike was definitely too rich before. It runs much more crisply now, still with good power. I still have the Main jets at 2 sizes richer than stock. Pulls really hard at WOT.
The only thing that puzzles me, is that the gas mileage is still the same, at about 43 MPG, as it was with the 4 mm. shimming. I have made the same run at least 50 times, and can usually predict the mileage within 5 MPG. The way I was riding, it was averaging in the low 50s before with stock Main jets and jet needles in the original single clip position. And I was riding easy - not over 1/4 throttle. I am surprised that 1 mm. hurt the mileage that much. Maybe there is something else going on, but I don't have a clue what it might be. Any ideas out there?
Thanks for all the replies.
If the airbox is still on the bike and the exhaust system is stock, you shouldn't need to go up 2 on the main jets.
You might try leaving the needles where they are and going back down to the main jets you had before.
The thing with fine tuning jetting is you have to try and see what's best.
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- 9am53
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- homebrew, and some bbq
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'84 GPz900r
'71 CB350
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- WABBMW
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I changed the pilot jets several years ago, from 37.5 to 40.0, and the gas mileage still averaged 53 to 57 MPG afterward.
I modified the exhaust slightly, but this was a couple of years ago. Gas mileage both before and after this modification stayed the same 53 - 57. The motorcycle did seem slightly lean after the MOD. All I did to the stock 4 into 2 system, was to weld in a smooth "Y" fitting between the pipes from cylinders 1 & 2, and also between 3 & 4. The original had an almost right-angle intersection where the pipes meet. Also the pipe exiting the "Y" toward the muffler is about 1 3/4". Mufflers have stock baffeling.
My gas mileage with the BS32 carbs always seemed to be higher than most other KZ650s, and I attributed this to what I thought was very lean jetting when stock. Then with the exhaust work, I decided to go 2 jet sizes richer on the Mains. This may have been a mistake, but I would think that it would not even come into the picture until about 3/4 throttle and above.
I still wonder if the larger Main jets are impacting the mileage and making the overall mixture richer. I have deliberately kept the throttle open no more than 1/4 at any time during this testing.
More comments and opinions are very welcome. Thanks.
Bill Baker
Houston, Texas
1982 KZ650 CSR
2008 Yamaha FZ1
2006 Yamaha FZ1
1977 Honda Supersport 750 four (sold)
1984 Honda Nighthawk 650 (sold)
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- TeK9iNe
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- What did you do!?!
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GL!
Motorcycle Shop Owner/Operator
79 Kawie Z1000 LTD
81 Kawie Z1000 CSR
83 Honda VT750C A
85 Kawie GPZ900 A2
86 Zukie GS1150 EG
93 Yamie XV1100 E
Lucky to have rolled many old bikes through my doors
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- 9am53
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- homebrew, and some bbq
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'84 GPz900r
'71 CB350
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- WABBMW
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Bill Baker
Houston, Texas
1982 KZ650 CSR
2008 Yamaha FZ1
2006 Yamaha FZ1
1977 Honda Supersport 750 four (sold)
1984 Honda Nighthawk 650 (sold)
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- Patton
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An incorrect fuel level will impact otherwise perfect jetting and fuel metering.
Good Fortune!
1973 Z1
KZ900 LTD
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- mark1122
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- Keep twisting it
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76 KZ, frame gusset work,1200CC.Ported by Larry Cavanaugh, 1.5mm.over intakes, Carron Pipe, ZRX12 rear end, and seat,96zx9 front end.
01 CBR600F4i Track bike.
Cobourg, Ont. Can.
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