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81 KZ750 with Airbox Jetting Question 24 Jul 2014 18:21 #641292

  • Mid life crisis
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Hi there.

I have been looking around the forums and see many jetting options. I have a 1981 KZ750-E2 with stock airbox and filter with a Vance and Hines 4 into 1.

It starts easily, idles well, and the bike responds to the choke setting, so I think my pilot circuit is fine. The issue I have is that the bike seems to be starving for fuel and stutters at cruising speed. The valves are in spec and the compression is fine. The fuel height has been checked and the carbs are clean.

I have all stock jets, except the secondary mains are 135s. Should I be changing the primary mains as well? I have the Keihin carbs.

Basically, I would like to know what other people are running with stock airbox and the 4 into 1 exhaust. I know this question has been asked many times, but I am unsure where to go next.

Thanks for any help on this.
1981 KZ750E2

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81 KZ750 with Airbox Jetting Question 14 Aug 2014 21:54 #644010

  • Zephyrrider
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Hey,
I run completely standard parts on my bike 94 ZR 750 :
Standard Motor -
Stock Airbox - K & N filter.
Formula 1 - 4 into 1
Keihin CVK 32 -
pilot Jet - #35
main - 1 and 4 - #88
2 and 3 - #92
2 turns out air screw
Always starts first time , runs beautiful
What are your air screws set at ?
I mucked about with the pilot jets years ago but didnt improve things in my case anyway,
Hope that helps in some small way.
Mick
1994 ZR750 Zephyr C4.

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81 KZ750 with Airbox Jetting Question 19 Aug 2014 18:27 #644545

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I think I finally have it sorted (or at least close to it). I have replaced the main jets with 140 secondary and 68 primary (I have the CV34 carbs). The bike now pulls nicely through all the gears. My frustrations have turned into smiles!

I have the screw out 2 turns, but I may play with that a bit.

Thanks for the suggestion. I appreciate the help.
1981 KZ750E2
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81 KZ750 with Airbox Jetting Question 19 Aug 2014 23:28 #644567

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2 turns out on the air/mixture screw works perfectly for me - good for a base/start point.
I used to have a Dynajet kit in my old CV 32's and air screws were 2 and a half out.
Thats bloody great to hear how your bike is now. Its a sweet feeling alright.
Mick
1994 ZR750 Zephyr C4.

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81 KZ750 with Airbox Jetting Question 20 Aug 2014 11:18 #644612

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Yep, it is a great feeling for sure! I still have a few tweaks to make (I will try 130 and 135 secondary mains), but at least I know that the bike can run well and that all the messing around is worth the effort. :woohoo:
1981 KZ750E2

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81 KZ750 with Airbox Jetting Question 20 Aug 2014 15:55 #644631

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Those smaller secondaries are a good idea for a try,
How does the bike feel just cruising at town and highway speeds and how is it out of a corner or up a hill under load?
Well worth the effort !
Looks like you would have some beautiful scenic roads where you are.
Mick
1994 ZR750 Zephyr C4.

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81 KZ750 with Airbox Jetting Question 20 Aug 2014 16:06 #644634

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I can cruise at 80-100 km/h with no issue. Doesn't seem to bog at all. I have been up a few hills and didn't notice any real issues. I will go out and put the bike through a couple of scenarios to see how well it performs at the top end under load. I will then change out the secondaries and see if there is a change.

So far, the bike runs well at cruising speed. I will go out and take a look at that great scenery tomorrow! I used to live in Australia, so I know that you have INCREDIBLE scenery. Lucky dog!
1981 KZ750E2
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81 KZ750 with Airbox Jetting Question 21 Aug 2014 14:16 #644722

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Sounds like you are getting very close to me. No surging or hesitation.Enjoy your Fine tuning. Does Canada use the metric system ,as you mentioned km/h.
Where i live is not very picturesque - a lot of sunburnt land , but i am not far from real nice rainforest country .
Mick
1994 ZR750 Zephyr C4.

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81 KZ750 with Airbox Jetting Question 22 Aug 2014 11:58 #644802

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It is nice to be close. It will take some time before I receive the jets, but at least I can ride around before the winter sets in.

I lived in Melbourne, so I was more used to the rain than sunburnt land! I did get a chance to travel of of your great country. I would like to bring my family some day.

Oh yeah; metric is what we use.
1981 KZ750E2

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81 KZ750 with Airbox Jetting Question 22 Aug 2014 14:55 #644816

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I would very much like to live in another country for a while ( Canada at top of list ) but the only drawback for me - No riding in winter.
Live in town of @12,000 - lots of sun , rarely rains so fairly different to Melbourne and ride all year round.
I would be very interested to see how you go trying the other jets . Enjoy your test riding.
Mick
1994 ZR750 Zephyr C4.

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