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TOPIC: Carb jetting

Carb jetting 01 Dec 2019 13:43 #814811

  • Trytobuildkzcafe
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I have a 80 kz750e with keihin carbs I believe are stock untouched and I’m going to put pods and Mac 4 to1 full exhaust. As far as changing the jets do I have to clip the slide springs and drill the slides ?or would I be able to replace main jets primary jets and and adjust mixture screw ( pilot jet ?) and adjust needle? Any help on this matter would be greatly appreciated since this will be my first attempt jetting a set of carbs.

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Carb jetting 01 Dec 2019 16:25 #814815

  • TexasKZ
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Leave the springs alone.
If Dynojet makes a stage three kit for that model, that will be the easiest way to start. Whatever you do, carefully save all the stock parts you take off in case you decide to go back. Otherwise, somebody else will need them.
1982 KZ1000 LTD parts donor
1981 KZ1000 LTD awaiting resurrection
2000 ZRX1100 not ridden enough

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Carb jetting 01 Dec 2019 16:56 #814817

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Ok don’t touch the springs! Thank you. As for drilling out the slides air displacement hole should I leave that alone too ?or does this need to be done?

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Carb jetting 01 Dec 2019 19:12 #814821

  • Nessism
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Buy the Dynojet kit and if they tell you to drill the slides, do it.

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Carb jetting 01 Dec 2019 19:42 #814823

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I had K&N pods and a mac 4 into 1 on my 1980 kz750 e1 for years with the primary main jets at 70 and the secoondary mains at 140. Cant remember how many turns out on the pilot mix screws.

Whatever route you take use good pods like K&N or APE. Some cheap pods block the air jets on the intake side
1980 kz750E1, Delkevic exhaust

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Last edit: by JR.

Carb jetting 02 Dec 2019 17:23 #814855

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I have a jet kit from 6sigma racing it came with step by step directions which are good but I’m a little confused because it says I’m drilling the slide to match the new spring tension after cutting it . If I’m not doing anything to the spring should I not drill the slide I have a tech support email I just haven’t email them yet? I was gonna get a stage 2 kit but it said if I use pods I need a stage 3.I have checked the pods, they do not block the ports so I’m good there! Thanks for the info everyone it is greatly appreciated!

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Carb jetting 02 Dec 2019 17:58 #814856

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Jr I have pretty much same set up 68 primary’s 137.5 for1&4 140 for 2&3 and I did check the pods they don’t block the air ports not sure what brand but they seem to be of good quality!

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Carb jetting 03 Dec 2019 03:56 #814868

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Trytobuildkzcafe wrote: I have a jet kit from 6sigma racing it came with step by step directions which are good but I’m a little confused because it says I’m drilling the slide to match the new spring tension after cutting it . If I’m not doing anything to the spring should I not drill the slide I have a tech support email I just haven’t email them yet? I was gonna get a stage 2 kit but it said if I use pods I need a stage 3.


As a rule, it is best to follow manufacture recommendations. The 6Sigma kits seem to have a good reputation, though I have no experience with them. Drilling the slide and lightening the springs are ways to quicken throttle response. However, I recon the spring cutting is based on relatively new spring strength, and yours are decades old and may not be close to new tension. If the springs end up too weak, the slides can flutter, giving you all sorts of headaches when trying to dial in the carbs. I have that T-shirt.
If that is what the Stage 3 kit calls for, then I would try it, but be aware of the pitfalls and be prepared to search for another set of springs if it does not work out.
1982 KZ1000 LTD parts donor
1981 KZ1000 LTD awaiting resurrection
2000 ZRX1100 not ridden enough

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Carb jetting 05 Dec 2019 10:32 #814954

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Talk with tech support from 6 sigma they said drilling slide and cutting spring is optional! Said these steps are used mainly in racing but it isn’t a necessary procedure for regular street riding thanks for the help every one

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Carb jetting 05 Dec 2019 22:41 #814970

  • loudhvx
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Drilling the slide just lets it open faster. If you don't care about maximum performance, it's not necessary. A smaller hole makes the slide more stable, but slower to react.

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Last edit: by loudhvx.

Carb jetting 07 Dec 2019 16:39 #815055

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Yea don’t think I’m ready to dig into it that far yet , took carbs apart today , don’t really know how the bike was running as well as it was carbs were very Dirty. Getting ready to put them back together with the new jets however the directions (a little confusing) say replace main jets with 137.5 1&4 and 140 2&3. If still lean go up one size. This I understand but after that it says replace pilot jets. The kit didn’t come with pilot jets. Does this mean replace pilots if it’s running lean? Or do I have to replace the pilot jets because I changed the primary and secondary jets?

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