Off idle mid range stumble

5558 Views 21 Replies 7 Participants Last post by mike toon, Jan 20, 2008

mike toon

Discussion Starter · Jan 1, 2008

I've had this 1981 KZ1000 CSR for two weeks now and I can't get rid of the stumble just off idle to about2,000 RPMs.

BS34 carbs with original 130 jets, airbox (removed for testing) and stock pipes.
All I've read indicates the pilot circuit is at fault. Carb cleaner and compressed air used.

Float level is ¼" down from top. Pilot jets have been removed and cleaned. I have removed the needle jets and cleaned but no obstructions. Needles are non adjustable (one groove) Two air screws are frozen but appear open because a good stream of carb cleaner comes out when sprayed in their holes. The other two are at 1½ turns out. Bike idles and top end (above 3,000 RPMs) is OK. Anything I may have missed?

1 - 20 of 22 Posts

A2rider

· #2 · Jan 1, 2008

Put the airbox back in and see what happens.

mike toon

Discussion Starter · #3 · Jan 1, 2008

A2rider said:
Put the airbox back in and see what happens.

The problem was there when I got the bike. I took it off to cure the problem. I would expect it to run lean but not "miss" without the airbox.

My KZ650 is basically the same, had one plugged pilot jet and after cleaning, ran fine......lean, but fine.

A2rider

· #4 · Jan 1, 2008

I have a KZ750 that runs on pods. Have it jetted correctly, but it has a slight stumble also. There will be someone on here soon that may be more help than I am. All I can think of is to keep messing with the jets, mixture screws.

Stormdragon

· #5 · Jan 1, 2008

It shouldn't have that stumble, I don't remember them having it originally. First question is have you had the valves adjusted and the carbs synched? That's one thing that should be done, just to rule out possible problems. I'd also suggest you get the frozen air screws fixed, since you have no idea what the settings are. In fact, I'd do that before synching the carbs as they would throw that off if you fix them afterwards. You could also look into an ultrasonic cleaning of the carbs, as that won't eat the gaskets, or require a full disassemble. You can also look into either getting a set of needles from Canada, which should have 5 positions AND a different taper to them, or find some really thin washers that you can slip under the stock needles, thus raising them a bit. It's really not the 'right' fix, but hey, if it works, it works.

elr658

· #6 · Jan 1, 2008

Well I don't know a darn thing about these bikes. Nothing. You have a better chance of seeing Courtney Love on a piece of rye toast than getting that ****er to run without an airbox. Now, back when I was young and stupid I tilted at windmills attempting to make the motorcycle in my signature go fast for cheap. K&Ns were my magic bullet. Now I am the smartest person I know. No lie. You need an engineering degree to play with me. Until a SAGE, BRILLIANT mechanic named Charlie Stoffa explained to me the relationship between a carburetor and its airbox about thirty years ago. The carburetor uses the differential pressure between the airbox and the slide chamber to LIFT the slides. NOW, no filter, or a pod CHANGES the relationship between the pressures and the SLIDE DON'T LIFT! ANYTHING that affects vacuum will DESTROY slide lift. What are the three things that will do that? Airbox, ignition timing, and VALVE LASH. Set to LOOSE side of the tolerance. Tolerances on that motor are .002-.006, set them so a .006 FALLS THROUGH and a .007 will not. Put the airbox back on after a real carb clean. Ignore the advice of a person who has used that EXACT motor for almost thirty years at your peril.

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95 Zx6R 2 GsXr

· #7 · Jan 1, 2008

wow,

almost made me want to do that to my bike and its completly diffrent bike, you should be a lawyer:shock:

elr658

· #8 · Jan 1, 2008

GSXR, haven't seen you around here. Where have you been? It is an accepted fact that "Modern Motorcycles" are tuned to within an inch of their lives. The days of picking up 10-25% with a pipe and a set of K&Ns are over. You need flatslides ($1200) a genius like me and a dyno. Kawasaki engineers are gearheads and leave NO easy HP as a matter of pride.

mike toon

Discussion Starter · #9 · Jan 1, 2008

Are we to assume anyone getting a KZ1000 to run properly with pods (+1 jetsize) and no other modifications, is doing the impossible?

Alizard

· #10 · Jan 2, 2008

mike toon said:
I've had this 1981 KZ1000 CSR for two weeks now and I can't get rid of the stumble just off idle to about2,000 RPMs.

BS34 carbs with original 130 jets, airbox (removed for testing) and stock pipes.
All I've read indicates the pilot circuit is at fault. Carb cleaner and compressed air used.

Float level is ¼" down from top. Pilot jets have been removed and cleaned. I have removed the needle jets and cleaned but no obstructions. Needles are non adjustable (one groove) Two air screws are frozen but appear open because a good stream of carb cleaner comes out when sprayed in their holes. The other two are at 1½ turns out. Bike idles and top end (above 3,000 RPMs) is OK. Anything I may have missed?

I can tell you I had the exact same problem on my 1979 KZ750 when I put on new headers. Increasing the pilot jet had a small improvement, but going two slots richer on my needles cured it and now it goes like a rocket.

You may want to buy a second set of needles and experiment with cutting new slots.

Alizard

· #11 · Jan 2, 2008

mike toon said:
Are we to assume anyone getting a KZ1000 to run properly with pods (+1 jetsize) and no other modifications, is doing the impossible?

No, but considering the time I wasted screwing around dialing in a set of MAC headers, we can probably assume the man with new pods has a hobby that will devour all of his free time.

Alizard

· #12 · Jan 2, 2008

elr658 said:
GSXR, haven't seen you around here. Where have you been? It is an accepted fact that "Modern Motorcycles" are tuned to within an inch of their lives. The days of picking up 10-25% with a pipe and a set of K&Ns are over. You need flatslides ($1200) a genius like me and a dyno. Kawasaki engineers are gearheads and leave NO easy HP as a matter of pride.

Even the car makers are getting hip and scooping up all the "low hanging fruit" when it comes to squeezing ponies out of an engine. My Cavalier has a 132 CID four banger that puts out 150HP stock trim (no turbo) and employs a tuned resonator on the intake side to maximize flow. Bikes really are tweaked to the max to get that kind of power out of the small displacements they run.

mike toon

Discussion Starter · #13 · Jan 2, 2008

bountyhunter said:
You may want to buy a second set of needles and experiment with cutting new slots.

No, but tell me the distance between slots and I'll try shims.

elr658

· #14 · Jan 2, 2008

The United States model J derivatives (KZ1000J,K,M,P,R all KZ1100s except GPz) use the EXACT SAME BS34 CV carb. The KZ1000R came with a FACTORY Kerker KR with a superbike baffle. (I put my bike together out of the crate) It ALSO came with the EXACT jetting that one with a stock pipe had. As long as the stock airbox, with stock air filter is retained, the stock jetting is the best. This is the case as a 998, 1075, 1089 or a 1260. My bike has run a 10sec 1/4 mile on stock jetting and airbox. Now, if you persist in your vain attempt to install K&Ns just throwing a set of needle shims (HD part #6048W to be exact)
you will succeed in wearing the emulsion tubes out because the needles can't float anymore. NONE of that is available anymore.

A2rider

· #15 · Jan 2, 2008

Holy Crap! 10 sec. 1/4 on a stock 25 year old bike? Sheesh, guys on ZX-14's can't do that. I might even take my POS 750 to the track next summer.

Alizard

· #16 · Jan 2, 2008

mike toon said:
No, but tell me the distance between slots and I'll try shims.

about .030" to .040"

StarGate

· #17 · Jan 2, 2008

mike toon said:
Are we to assume anyone getting a KZ1000 to run properly with pods (+1 jetsize) and no other modifications, is doing the impossible?

It may not be "impossible" but thats where my vote would go. I tried, off and on, for about 10 years of the almost 27 I have owned this one and finally gave up. I'm now running factory exhaust/airbox again and happy about it. I was able to get different variations, low/mid/high range, to run great but never all 3 at the same time. There was always something not quite "right" with the way it ran (mostly low end). As for the shims under the needle clips, mine came factory with 2 under each and they are back in there as well. The biggest and most noticeable problem that I lived with during that time was the lack of throttle response/smoothness when under 2k rpm that you mentioned. Not a lot of fun on gravel.

elr658

· #18 · Jan 3, 2008

Honey, my bike ain't stock. Hasn't been since 1982. Ran a 10 in 1983.

A2rider

· #19 · Jan 3, 2008

elr658 said:
Honey, my bike ain't stock. Hasn't been since 1982. Ran a 10 in 1983.

OK, you said stock jets and box. So we're talking exhaust, gearing, chain, sprockets, turbo. I know you wouldn't NOS it!

I can't blow this up any more, but I don't think I can see a turbo. You are very stingy with pictures of your bike. I can't afford a plane ticket to where you're at, so this will have to do me.

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elr658

· #20 · Jan 3, 2008

That's not my bike. That one belongs to my friend Kevin.
1325cc, 13.5:1, 118 octane leaded gas, BIG cams degreed to 108 lobe centers, 130 lb pro rider, SERIOUS weight reduction, rear wheel widened by Kosman, slick, struts and wheelie bar. Front suspension tied down. MSD ignition.

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