82 GPZ750 carb swap jetting

  • Tune-A-Fish
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82 GPZ750 carb swap jetting

09 Aug 2016 15:21
#738027
Hello all... I have recently purchased a nice GPZ750 and it came with a nice set of KeiHin CVK G488 ANFV carbs Look to be off of a ZR750

Pulled them down to inspect because of poor idle and rich plugs All looks clean and clear, but I can only get it to run on choke (rich plug and poor idle off choke) What I would like to know first is if anyone has done the mod and if so can I get your baseline jetting and air screw setting. I have the air box and filter setup, but running pods (K&N Big ovals) for tuning in the shop to get close, then I will swap to air box.

I also have the stock carbs, but the jets are not readable and may be aftermarket junk, they are also all apart with no rail.

Thanks in advance for reading and any thoughts forthcoming.
Tune
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Re: 82 GPZ750 carb swap jetting

09 Aug 2016 18:48
#738048
If it is a cvk32 carb set from a Zephyr zr750 then they "should" work pretty well with factory settings as the '82 motor is virtually identical in a mechanical sense to the zr750. (cams, compression...etc.)
So with factory jetting and an airbox it should work very well.

Factory settings are:
Cylinders 1 and 4 Main Jets: 88
Cylinders 2 and 3 Main Jets: 92
Idle adjustment screw: 2 1/2 turns out
Stock needles do not have adjustment.
Float Height: 17mm (this is important)
Check the vacuum diaphragms for small rips or tears.


You will not be able to road test this factory jetting setup with pods on!! It won't work at all....like at all!
So first (before you buy rebuild kits or anything for the cvk's) you need to try to make the stock gpz airbox work with the cvk32 carbs. If you can't make the airbox work you need to decide whether to find stock carbs, or invest in a Factory Pro Stage 3 kit (for the Zephyr 750) to use with the pods and the cvk32's. Otherwise they will never work properly and you run the risk of accidentally running lean and destroying your motor.

Just food for thought.
1990 zr550
kz750e
650/750 6-speed Transmission Swap


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Re: 82 GPZ750 carb swap jetting

09 Aug 2016 19:28
#738056
Daftrusty wrote: If it is a cvk32 carb set from a Zephyr zr750 then they "should" work pretty well with factory settings as the '82 motor is virtually identical in a mechanical sense to the zr750. (cams, compression...etc.)
So with factory jetting and an airbox it should work very well.

Factory settings are:
Cylinders 1 and 4 Main Jets: 88
Cylinders 2 and 3 Main Jets: 92
Idle adjustment screw: 2 1/2 turns out
Stock needles do not have adjustment.
Float Height: 17mm (this is important)
Check the vacuum diaphragms for small rips or tears.


You will not be able to road test this factory jetting setup with pods on!! It won't work at all....like at all!
So first (before you buy rebuild kits or anything for the cvk's) you need to try to make the stock gpz airbox work with the cvk32 carbs. If you can't make the airbox work you need to decide whether to find stock carbs, or invest in a Factory Pro Stage 3 kit (for the Zephyr 750) to use with the pods and the cvk32's. Otherwise they will never work properly and you run the risk of accidentally running lean and destroying your motor.

Just food for thought.

Thats awesome! I do have an air box for the carbs that fits with some moving of the battery box, the bike amazingly came with both air boxes. I am very aware of the pods and CV type carbs, typically pods dont provide anything more than esthetics or ease of carb remove/installs on street bikes. This is why I made it clear I'm not intending to run it open air with the k&N's.... unless I get a stage 3 kit, but Z1 didn't have it for this.
The mains are 110's, pretty fat compared to your #'s and couldn't read the pilot's.. did you have a pilot jet number btw?

: 1)Carb in question 2) stock carbs 3) PODS :)


Attachment cv1.JPG not found



Attachment StockCV.JPG not found



Attachment cv2.JPG not found





Thanks a ton mang!

Tune
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Re: 82 GPZ750 carb swap jetting

09 Aug 2016 19:44
#738060
Sorry,
The Pilot Jet is 35

Normally the Zephyr 750 carbs didn't come plastic diaphragm lids but the Zr-7's did. Is there a throttle position sensor on one side of the carbs? If so the specs I gave you are totally wrong.
1990 zr550
kz750e
650/750 6-speed Transmission Swap


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Re: 82 GPZ750 carb swap jetting

09 Aug 2016 19:59
#738065
After doing more research, you most likely have cvk32's from a 1985-97 zx600.
They are the exact same carb bodies just with a multitude of different needles, needle jets, main jets and pilot jets...etc.
More investigating is needed.
1990 zr550
kz750e
650/750 6-speed Transmission Swap


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Re: 82 GPZ750 carb swap jetting

09 Aug 2016 20:06
#738068
Daftrusty wrote: After doing more research, you most likely have cvk32's from a 1985-97 zx600.
They are the exact same carb bodies just with a multitude of different needles, needle jets, main jets and pilot jets...etc.
More investigating is needed.
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Re: 82 GPZ750 carb swap jetting

09 Aug 2016 20:08
#738071
Daftrusty wrote: Sorry,
The Pilot Jet is 35

Normally the Zephyr 750 carbs didn't come plastic diaphragm lids but the Zr-7's did. Is there a throttle position sensor on one side of the carbs? If so the specs I gave you are totally wrong.

Yes, It has a TPS sensor.
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Re: 82 GPZ750 carb swap jetting

09 Aug 2016 21:31 - 09 Aug 2016 21:34
#738081
Ah...TPS means they are from a zr-7.
Which is good as the zr-7 is identical to the '82 gpz750 mechanically and performance wise.
So the stock settings are as follows.

1990 zr550
kz750e
650/750 6-speed Transmission Swap


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Re: 82 GPZ750 carb swap jetting

10 Aug 2016 04:55
#738089
Ahhh well the 110's are closer then and with a 4-1 header (mac mega yosh header) I may even be lean when I get out on the road.

Still it's failing on the idle circuit so must need to look closer at the pilots and maybe give the needles a look the see if someone has botched things.

Thanks for diggin up the specs! beyond expectations,

Tune
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Re: 82 GPZ750 carb swap jetting

10 Aug 2016 04:57
#738091
Oh also I performed the usual 1.5 turns on the fuel screw so maybe the extra .25 will be magic! Highly doubtful tho :/
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Re: 82 GPZ750 carb swap jetting

10 Aug 2016 05:45
#738098
The more I thought about it...1 3/4 turns is very lean setting. And I remembered reading about the zr-7 "low speed stumble" and wondered if this was partially due to the factory idle speed setting and this is what I found.





Richening the idle mixture by turning out the screw may help.
But as you mentioned, I would recheck to make sure the previous owner didn't accidentally mix up the needles or the emulsion tubes as they are both different between the 1&4 and 2&3 cylinders.
I wish you the best of luck, as I also have a set of cvk32's to put on my kz750 when I finally get the motor back together. So your success will give me hope that I will also succeed.

Cheers
1990 zr550
kz750e
650/750 6-speed Transmission Swap


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Re: 82 GPZ750 carb swap jetting

10 Aug 2016 05:56
#738099
Yessir! I planned to pull them anyway for the pilots and I actually like tuning carbs, but always nice to have a known baseline to save a lot of guesswork.
As a side note beings that you are working on the same motor... My compression (cold open intake all plugs out) was 152 154 162 154 ish >< 1 for bad eyesight... Just so were comparing apples to apples, I will pull another comp test once I can get an idle with even cylinder temps.
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