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Jet needle improves acceleration. 09 Jul 2011 18:17 #461912

  • calvin17d
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Disregarding the plug readings, the transition to the main from the needle was in fact progressive and has been impressive since the increase on the needle height. The acceleration seems to have improved with the jet needle up, but I would give it an overall rating of weak. I don't feel I could get the front end up yet but it's getting close and very fun to ride.
1976 Kz900 A4

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Jet needle improves acceleration. 09 Jul 2011 21:17 #461933

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I went about trying this method and spent about twenty mins riding around in first gear. I pulled over and idled while I took a quick stretch. I must have started to foul the plugs because my exhaust was now smoking like never before.

The finding was not backfiring at all but rather my bike is surging as you suggested. This might explain my rich plug chop from this morning at 1/8-1/4 throttle.

Rich 17.5 (stock) pilots with pod filters?
1976 Kz900 A4

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Jet needle improves acceleration. 09 Jul 2011 23:54 #461950

  • DoubleDub
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I have a basically stock Kz900 also, with pods, and a 1075 kit. I had to go to the 120 mains also, but found that raising the needle created the same issues you are reporting. I went back to stock location, synch'd the carbs, tuned the idle air screws, and everything runs great. I'm pretty sure the idle/pilot mixture does not need to be touched for pods with the VM26's on these bikes - they were pretty rich from the factory.

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Jet needle improves acceleration. 10 Jul 2011 00:05 #461953

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DoubleDub wrote: I have a basically stock Kz900 also, with pods, and a 1075 kit. I had to go to the 120 mains also, but found that raising the needle created the same issues you are reporting. I went back to stock location, synch'd the carbs, tuned the idle air screws, and everything runs great. I'm pretty sure the idle/pilot mixture does not need to be touched for pods with the VM26's on these bikes - they were pretty rich from the factory.


Man... The raised needle Was helping with the poor acceleration. I had a feeling this was contributing excess fuel. I don't know the first thing about tuning in the needle and needle jet which is sounding like where the problem is. Is there ant reason why going to a 15 pilot would be less suitable then going for an alterernate taper?

I am wondering what the effect will be with needle at stock position and a larger pilot?
1976 Kz900 A4

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Jet needle improves acceleration. 10 Jul 2011 00:08 #461955

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Have you verified all other factors? Ignition timing, compression, valve clearances, etc.

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Jet needle improves acceleration. 10 Jul 2011 00:29 #461958

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DoubleDub wrote: Have you verified all other factors? Ignition timing, compression, valve clearances, etc.


Yes multiple times each. I triple check all my work in a very methodical manner.

I will have to replace the needle and run through that driving pilot test again. That worked quite well.
1976 Kz900 A4

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Jet needle improves acceleration. 10 Jul 2011 01:46 #461972

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Dont forget to correctly "tune" your mixture/air screws.

With pod filters, they wont be at the same "X" number of turns out.
Just about a half turn leaner from when you can produce a rich stumble on the mix screws (and not less than 1/2 turn from closed), is where the point of easiest combustion is. Highest idle note.

Turn the screw richer till the engine becomes noticably stumbly/rpms drop 200 or more, then turn it back 1/2 turn.

You will find that the screws will all be at slightly different postitions - because they should be.

Good luck.

B)
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Jet needle improves acceleration. 10 Jul 2011 11:14 #462018

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[quote
Man... The raised needle Was helping with the poor acceleration. I had a feeling this was contributing excess fuel. I don't know the first thing about tuning in the needle and needle jet which is sounding like where the problem is. Is there ant reason why going to a 15 pilot would be less suitable then going for an alternate taper?

I am wondering what the effect will be with needle at stock position and a larger pilot?[/quote]

that is a good question and u should try it. this is a great way to learn how each adjustment affects the bike.

But, before u do though, i would play with the pilot jets some more. since u said it felt better with more needle , i would not abandoned that setting yet.
what do your notes say about the 20 min of testing in 1st gear? did it stumble at first and then get better with each new adjustment until it fouled? Did u try it at dif rpms and take notes?
adjusting the pilots as Tek9 suggested is the normal way to start tuning the pilots. u adjust them 1 at a time to achieve the highest rpm at idle note. if u have to go less than a 1/2 turn out or more than 2.5 u would change to the next size pilot jet.
76 kZ, frame gusset work,1200CC.Ported by Larry Cavanaugh,This email address is being protected from spambots. You need JavaScript enabled to view it., 1.5mm.over intakes,.ZRX12 rear end,and seat,96zx9 front end.
01 CBR600F4i Track bike.
Cobourg,Ont.Can.

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~ (k) / (z)

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Jet needle improves acceleration. 10 Jul 2011 11:50 #462029

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Driving in first and observing engine performance I noted surging most noticeably at 2K rpm's. It was however present at 1-3 & 4K as well. Approaching 5K the surge went away. I assume this was where a transition was occurring. Prior to heading out, I did in fact tune the mix screws as suggested. After Finding the optimum rpm at idle how would one begin tuning after a driving test that revealed a rich condition?

Lean all screws an 1/8 a turn and try the riding test again?

If I understand this, we are saying that a good idle tune of the mix screws may not directly translate to a good tune under load?
1976 Kz900 A4

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Jet needle improves acceleration. 10 Jul 2011 12:14 #462039

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calvin17d wrote: Driving in first and observing engine performance I noted surging most noticeably at 2K rpm's. It was however present at 1-3 & 4K as well. Approaching 5K the surge went away. I assume this was where a transition was occurring. Prior to heading out, I did in fact tune the mix screws as suggested. After Finding the optimum rpm at idle how would one begin tuning after a driving test that revealed a rich condition?

Lean all screws an 1/8 a turn and try the riding test again?

If I understand this, we are saying that a good idle tune of the mix screws may not directly translate to a good tune under load?


i feel that way.

as u richened the pilots during the 1st gear test, was it obvious that the bike was running smoother/better at some rpms? how many turns out were the srews before and after ther 1st gear test ?
76 kZ, frame gusset work,1200CC.Ported by Larry Cavanaugh,This email address is being protected from spambots. You need JavaScript enabled to view it., 1.5mm.over intakes,.ZRX12 rear end,and seat,96zx9 front end.
01 CBR600F4i Track bike.
Cobourg,Ont.Can.

~ ~ ~_@
~ ~ _- \,
~ (k) / (z)

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Jet needle improves acceleration. 10 Jul 2011 12:31 #462044

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I did not get a chance to make any adjustments to the first run on the first gear test. I was unclear on how this should be done? If I had a rich result (surging) during my first gear test, would I simply turn the screws out uniformly?
1976 Kz900 A4

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Jet needle improves acceleration. 10 Jul 2011 12:34 #462045

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I did not get a chance to make any adjustments to the first run on the first gear test. I was unclear on how this should be done? If I had a rich result (surging) during my first gear test, would I simply turn the screws out uniformly and test again?
1976 Kz900 A4

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