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Jetting for 76 kz900ltd

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QITMAN
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Jetting for 76 kz900ltd

#1 PostAuthor: QITMAN » Fri Jan 12, 2018 2:16 pm

Hi all
Just wondering if any of you can shed some light on what jets I would need for my above bike. The carbs are std ones and the bike ran well with my old V&H and Harris exhausts on, but I’ve got the 4-4 ones on now and it seems not to pull so well.
I’m going to put it on a rolling road in the spring and would like to save costs by putting in jets which will work with out the tech having to pull the carbs off to rejet
Any ideas
Thanks
Mike
Z900, Tuono RSV 1000, YZF1000R, XL600R, DT100, GSXR750 SLABSIDE

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ZedHead
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Re: Jetting for 76 kz900ltd

#2 PostAuthor: ZedHead » Fri Jan 12, 2018 2:40 pm

Standard Z900 jetting

jet needle 5DL31-3
needle jet 243 0-6
main jet 115
slow jet 17.5

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Re: Jetting for 76 kz900ltd

#3 PostAuthor: zed1015 » Fri Jan 12, 2018 2:44 pm

If the 4-4 pipe is a pattern one it's very likely that the problem is with the pipe and no amount of re-jetting etc will sort it out.
I've had at least 10 zeds through my hands lately that wouldn't pull the skin off a rice pudding and struggled to reach a ton and all of them only had this trouble after the pattern 4-4's were fitted.
It appears that many pattern 4-4's have been made with very restrictive internals and the choice is either go for stock looks with the 4-4 or performance with a decent 4-1.

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Re: Jetting for 76 kz900ltd

#4 PostAuthor: PAULJAC47 » Fri Jan 12, 2018 5:16 pm

/Interesting that re the 4/4,s...how recently have those pipes been problematic? last couple of sets i fitted seemed fine!purchased 2 yrs back...
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Re: Jetting for 76 kz900ltd

#5 PostAuthor: ZedHead » Fri Jan 12, 2018 6:12 pm

The pattern 4 into 4 exhausts should be no more restricted than the original Z900, which were slightly more restricted than earlier Z1.

I was wondering if it was possible that the jetting on quitman's z900 had been increased to compensate for a weak mixture caused by a freer flowing 4 into 1? The reverse presumably would result in rich running and incomplete combustion.

Ultimately, a Dyno test will probably indicate that some improvement can be gained from re jetting. It may be prudent to wait and see what the tests say.

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Re: Jetting for 76 kz900ltd

#6 PostAuthor: zed1015 » Fri Jan 12, 2018 6:16 pm

PAULJAC47 wrote:/Interesting that re the 4/4,s...how recently have those pipes been problematic? last couple of sets i fitted seemed fine!purchased 2 yrs back...


Some of the bikes had 4-4's fitted a few years back as part of long term resto's and others more recently.
I don't know the dates of purchase so don't know if it's a particular batch or an on going thing.
All suffered with shite performance beyond around 70 mph which most owners (especially the resto's who never ran the bikes with anything other) didn't realise was not normal until pitched against another comparable bike with full power while out on a club run etc
After pulling out all the stops to gain a few mph here and there non of the bikes would break the ton even with determined thrashing.
They were all revs but no guts and felt strangled.
As soon as an alternative pipe was tried they would sail way past the ton with the arm pulling ease that they should.
Apparently ( so i'm told ) some of these pattern 4-4's have internals modelled from one particular year which is more restricted than the rest.
The trouble with a lot of this pattern stuff is that it's more about the "look" than the function.

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Re: Jetting for 76 kz900ltd

#7 PostAuthor: kev edwards » Sat Jan 13, 2018 8:16 pm

What Carbs Air screw or pilot screw, 26mm or 28mm?

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Re: Jetting for 76 kz900ltd

#8 PostAuthor: QITMAN » Sun Jan 14, 2018 2:15 pm

26mm
The bike was never as fast as the models with the larger carbs bu went up to 120 with ease.
Just feels sluggish now. Think I will wait for the dyno run and see what happens.
PS it probably doesn’t help riding the Tuono :D
Thanks for the replies
Mike
Z900, Tuono RSV 1000, YZF1000R, XL600R, DT100, GSXR750 SLABSIDE


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