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Discussion Starter · #1 ·
Hi.

Im new to the forum so hello to everyone especially fellow ZX9R owners.

My ZX ownership started very recently when a couple of weeks ago i brought my very first ZX9R. Its a 98 C1 model in fairly good condition with 34k on the clock. It has some lovely add ons including a full Akrapovic system with K&N filter and Harris rear sets amongst others but i have a problem that I'm hoping someone on here will be able to help me with.

The bike pulls very well and has nice precise gear changes but at around 2.5k rpms in any gear the bike kind of stutters and shudders when held at that rpm.

It's very off putting when laying the bike down into a corner at that rpm and makes the otherwise excellent handling feel a little unstable.

Has anyone else experienced this?

I haven't checked anything mechanical on the bike yet but just wondered if anyone could give me some pointers.

I appreciate your time.

Thanks.
 

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All too well. It's called surging. That's the fueling transition zone between the carb's pilot fuel circuit and the mid-range circuit (jet needle). Most carb'ed bikes will experience what you describe in the 2,500 - 3,000 RPM range and most noticeably after mods are completed that effect the bike's breathing (air filter & pipe). The cure is well documented in the 9R section, if nothing else. It will require cleaning the circuits and the jetting be adjusted to add slightly more fuel to the pilot circuit or the jet needle to smooth things out AND just as importantly the carbs have their pilot air screws set evenly before being synchronized.

It's a compromise and it's not perfect, but it does go a long way in making the bike more civil to ride in that RPM range.
 

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All too well. It's called surging. That's the fueling transition zone between the carb's pilot fuel circuit and the mid-range circuit (jet needle). Most carb'ed bikes will experience what you describe in the 2,500 - 3,000 RPM range and most noticeably after mods are completed that effect the bike's breathing (air filter & pipe). The cure is well documented in the 9R section, if nothing else. It will require cleaning the circuits and the jetting be adjusted to add slightly more fuel to the pilot circuit or the jet needle to smooth things out AND just as importantly the carbs have their pilot air screws set evenly before being synchronized.

It's a compromise and it's not perfect, but it does go a long way in making the bike more civil to ride in that RPM range.
+1He's 100% correct.:smile
 

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Discussion Starter · #4 ·
Thanks for the quick reply e1_ZX-9r.

I see. Well explained thanks. I was worried it was something more serious. It feels very similar to an old fuel injected bike i had that was made to run lean at around 3.5k rpms to get it through emission regs test.

I suppose the only other thing to do is to ride around it and take the corner in a higher gear and avoid that area. Otherwise what you said.

I will sync the carbs, check plugs/spark and air filter when i get a chance just to make sure none of that is adding to the problem.

Have you or do you know of anyone using a Morgans Colourtune? Results?

Thanks a lot.
 

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my bike is a little older than yours, and it had the 3k transition issues as well. I richened up the floats (were 14mm now 12 - 13mm) and it significantly helped.
 

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my bike is a little older than yours, and it had the 3k transition issues as well. I richened up the floats (were 14mm now 12 - 13mm) and it significantly helped.
Oh yeah, duh! That too.

Morgan CarbTune Pro 4, search ZXF for Carburetor synchronization and select the 45-minute how-to from the results.
 

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If you really wanna be fancy spring for the #40 Pilot Jets (Kawasaki Part #92064-1108) instead of having the #38's turned out an extra 0.5 turn :evil
 

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Discussion Starter · #10 · (Edited)
Right guys, I'm just about to get the tank up and get those carbs off. Im not putting in new jets, just going to modify whats there.

Whats best? Richen up the floats by a mil or two like Rick S said or turn out the pilot screws by 0.5 of a turn like D-CON said?

Also it may sound like a stupid question but how do i make sure the pilot air screws are set all the same before i sync the carbs? Wind them in to work out how many turns and then wind them back out and make sure they are all the same? i have a Haynes manual.

Thanks guys. Your advice is greatly appreciated.
 

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Right guys, I'm just about to get the tank up and get those carbs off. Im not putting in new jets, just going to modify whats there.

Whats best? Richen up the floats by a mil or two like Rick S said or turn out the pilot screws by 0.5 of a turn like D-CON said?

Also it may sound like a stupid question but how do i make sure the pilot air screws are set all the same before i sync the carbs? Wind them in to work out how many turns and then wind them back out and make sure they are all the same? i have a Haynes manual.

Thanks guys. Your advice is greatly appreciated.
Last edited by Big Green Mean Machine.; 07-05-2012 at 05:26 AM. Reason: spelling..
Float height or turns on the pilot air screw? It may be both and if you're pulling the carbs out of their boots, I'd advise you record the settings for both and compare them to your Haynes.

The air screws are recorded as you said, turning gently until they seat.

And thank you Big Green for checking your spelling, it's much appreciated. Few things are more distracting when trying to advise someone than having to weed through an unpunctuated incoherent 20 row run-on sentence full of misspellings and no capitalized words. :mfclap
 

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Discussion Starter · #12 · (Edited)
Thanks e1.

Well this afternoon I got well acquainted with my 9r. I took each carb to bits and cleaned them including all the jets, checked each float level which were all at 13mm which according to the Haynes manual is correct. I then checked all the pilot air screws and each one was different so I've set them all at 2.5 turns out. Standard setting is 2 turns. I then synced the carbs and so far so good...

I now have an issue with my neutral light that wont come on and i can only start the bike with the clutch pulled in!

I'm hoping I've just pinched a wire or disconnected something somewhere...
 
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