Main jet

Kiddynamite8
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Main jet

28 Sep 2019 10:26

Hi guys. Need some help.
1978 kz650. I'm cleaning up the carbs because it ran like crap, and ultimately just failed to start.

I have 117.5 Main jet. The only mod done to the bike was a vance and hines 4-1 exhaust (previous owner)

Does that jet size sound right? I read that 112.5 was the stock size?

As always, any help is appreciated. Thanks.

1978 KZ650

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Warren3200gt
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Re: Main jet

28 Sep 2019 10:55 - 28 Sep 2019 10:58

#811473

Some 4 -1 dont need re jet others do.
Dont think V & H do but never had one so not 100%. What do your plugs look like?

Z1000J2 somewhat modified!

Last edit: 28 Sep 2019 10:58 by Warren3200gt.

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martin_csr
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Re: Main jet

28 Sep 2019 10:57 - 28 Sep 2019 11:04

#811475

I don't know what size the stock main jets would be, but 112.5 sounds too big & 117.5s might be too large for just the 4-into-1 exhaust.
With the 4-1 & individual pod filters those 2 sizes would be in the ball park. The KZ650.Info site has quite a few carburetor stickies, including a jetting guide The diagrams at Partzilla list 4 sizes for the 1978 KZ650-C2 >> 92.5 to 107.5.

ps: good pic.
...

1981 KZ650 Competition Sports and Road

Last edit: 28 Sep 2019 11:04 by martin_csr.

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Kiddynamite8
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Re: Main jet

28 Sep 2019 12:05

#811480

The plugs were pretty blacked up.
The bike has the stock airbox.

If this setup would work with pods, that would save the headache of reinstalling!

So do you guys ageee that the 117.5 is too big for the stock airbox and the V&H exhaust?

I'd love to figure out the right combo.

Thanks guys!

1978 KZ650

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SWest
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Re: Main jet

28 Sep 2019 12:20

#811481

When was the last time the valves were adjusted? V/H only needs two steps on the pilots and one on the main or more with the comp. baffle.
Steve

Z1b1000 1975 Z1b
kzrider.com/forum/11-projects/598262-kz-...-will-it-live#672882
kzrider.com/forum/2-engine/597654-poser?start=240#704229

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gd4now
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Denco where did you go?
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Re: Main jet

28 Sep 2019 14:10

#811485

I think 117.5 main would be too large. Stock carbs for 78 were either vm24ss or vm22ss . The 24's came with 102.5 mains and the 22's came with 90 mains. I have a 77 B1 with the stock vm24ss carbs and am running pods and a Denco 4 into 1 and have 17 pilots and 110 mains and it may be a little fat.

1977 KZ650 B1
Pods and Denco header

OLD KAW OWNERS SMILE ALOT

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Kiddynamite8
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Re: Main jet

28 Sep 2019 15:04

#811486

Thanks for the info! A fellow kzrider member showed me that I have vm24s.

I think I'll try the 110 mains with the 17 pilots and see if that makes things right.
Thank you.

1978 KZ650

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650ed
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Re: Main jet

28 Sep 2019 18:45

#811487

I highly recommend you keep that airbox on it. Ed

1977 KZ650-C1 Original Owner - Stock (with additional invisible FIAMM horn)

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SWest
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Re: Main jet

28 Sep 2019 18:51

#811488

AGREED

Z1b1000 1975 Z1b
kzrider.com/forum/11-projects/598262-kz-...-will-it-live#672882
kzrider.com/forum/2-engine/597654-poser?start=240#704229

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Kiddynamite8
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Re: Main jet

28 Sep 2019 21:24

#811493

100% keeping the stock air box.
I will listen to the pros!

Also, gonna try running the 102.5 Mains and see what happens.

You guys have no idea how valuable your knowledge is to a noob like myself. THANK YOU.

1978 KZ650

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hardrockminer
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Re: Main jet

29 Sep 2019 05:41

#811495

You may want to also consider replacing the needle jets and the jet needles. Most people don't realize that they wear over time. A new set will bring your carburetors back to original function. You can probably buy complete new kits (I like Keyster) from Z1 enterprises.

I have several restored bikes along with a 2006 Goldwing with a sidecar. My wife has a 2019 Suzuki DR 650 for on and off road.

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650ed
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Re: Main jet

29 Sep 2019 06:02

#811496

hardrockminer wrote: You may want to also consider replacing the needle jets and the jet needles. Most people don't realize that they wear over time. A new set will bring your carburetors back to original function. You can probably buy complete new kits (I like Keyster) from Z1 enterprises.

I guess I'm one of those folks. My bike still has the original Mikuni needle jets and jet needles and with 62,000 miles they still work like they did when the bike was new. Ed

1977 KZ650-C1 Original Owner - Stock (with additional invisible FIAMM horn)

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