TOPIC:

Are you saying you have not split the carbs apart, pulled the slides and all that?

missionkz wrote: Are you saying you have not split the carbs apart, pulled the slides and all that?

I have not. What would that possibly accomplish? I'm not having a bulk fuel delivery issue, or leaky fuel transfer fittings, or anything like that. Since I can't gain anything by splitting the carbs, all it can do is cost me when something breaks.

zukdave wrote:

jackleberry wrote: [Have already done this with Seafoam.

Maybe if you used some real carb dip like Berrymans and not snake oil
you might just get them clean. Myself I'd break them down and find a shop that has a sonic cleaner
and have them cleaned right.

Can't deal with caustic right now. Besides, I'm not at all convinced that cleanliness is the problem. The pilot circuits pass both air and carb cleaner and the idle mixture screws have the intended effect. To me, this indicates quite clearly that the passages are not blocked. Clean is clean, is it not? You can't get any cleaner than that.

Are the diaphragms hard?
Steve

swest wrote: Are the diaphragms hard?
Steve

No, they're in great shape and the slides move just as freely as the ones in the other bike, as far as I can tell.

jackleberry,

I was poking around the forum and found a couple of great Tech articles you might find of guidance on your persistent flat spot off idle.
Lots of good information. Good luck. I feel your pain. The initial start-up of my 1994 KZP1000 once I finished a ground up rebuild of the bike, was brought to a halt due to rough idle and limited performance. Most of my issues were due to having added air pods and a 4 into one header which required rejetting of the carbs as well as bumping up the pilot jet size. took me a bit to dial it in but end result is a great running bike. Hang in there, you will figure it out!

Helpful links: www.kzrider.com/articles/technical-tips/123-carb-cleaning-101
www.kzrider.com/articles/technical-tips/124-carb-cleaning-102

Copbike1000 wrote: jackleberry,

I was poking around the forum and found a couple of great Tech articles you might find of guidance on your persistent flat spot off idle.
Lots of good information. Good luck. I feel your pain. The initial start-up of my 1994 KZP1000 once I finished a ground up rebuild of the bike, was brought to a halt due to rough idle and limited performance. Most of my issues were due to having added air pods and a 4 into one header which required rejetting of the carbs as well as bumping up the pilot jet size. took me a bit to dial it in but end result is a great running bike. Hang in there, you will figure it out!

Helpful links: www.kzrider.com/articles/technical-tips/123-carb-cleaning-101
www.kzrider.com/articles/technical-tips/124-carb-cleaning-102

Thanks. I've been methodically richening the idle mixtures 1/8th turn at a time starting from highest vacuum and test riding. It just started getting interesting because I dipped into 'too rich' territory and had to raise the idle via the curb idle screw (which changes the dynamics of the whole thing). It's weird. I can feel the the performance shift around through this process what with the different warm up times, backfiring vs popping, etc, but the feeling of flatness or powerlessness of the throttle off idle seems constant. I think I'll keep going (richening and raising the idle to compensate) for a few more cycles and see what happens. However, I have my doubts, because I bench sync'd the carbs on both bikes in exactly the same way, and used exactly the same dynamic mixture tuning and carb sync methods & tools.

So far what I'm planning for the next serious step is just to take the carbs out again and replace the stock pilot jets with the next size up and try threading some mono-filament or guitar string all the way through the pilot circuit passages. I think I'll measure the slide springs too, although I have no idea how long they're supposed to be (and don't have a strong enough reason to pull the carbs on the other bike again and measure those).

FWIW, the bike idles smooth, runs smooth, everything is perfect except for feeling like a 250cc motor for the first little twist of the wrist. I'm basically all out of things to replace/tune up at this point...

The cop bikes are are geared low. The bike might have some taller gear now. Also since everything is stock and having done multi synchs, carbs cleaned and adjusted, check the linkage not worn out. Return spring stretched out or not on right and butterflies have snappy opening and close.

Olajoe wrote: The cop bikes are are geared low. The bike might have some taller gear now. Also since everything is stock and having done multi synchs, carbs cleaned and adjusted, check the linkage not worn out. Return spring stretched out or not on right and butterflies have snappy opening and close.

It has a 2.33:1 gearing ratio (530 sprockets and chain). I thought perhaps that was the problem and spent a lot of time and money getting the ratio on this bike closer to the other (2.20:1) hoping that the gearing would move/cover up the flat spot in the throttle response, but the changes in gearing really had no effect on the issue.

The throttle linkage and spring is tight and strong.

Replacing your pilot jets with the next size up sounds like a good plan. I have a funny feeling that you are now on the right track to solving this. Keep us posted........

P.S., As I am sure you might have already figured is that, you will more than likely need to bring the adjustment screws back down to a base-line setting and go from there with the larger replacement pilots. Good luck!!!!

I had the same issue with idle to quarter throttle response. I bought a 1982 gpz 750 last August. The seller had the carbs rebuilt, wgcarbs out of Texas. The bike has pods and pipe installed, previous owner always had to start bike with ether and choke to keep it running. I found out pilot jets were turned out 1.5 turns out, Throttle response was non existent from 1dle up to quarter throttle, opened up pilot jets to 2.5 turns, not totally dialed yet because of winter conditions, but a major improvement in throttle response. Quarter up throttle was never and issue, I would surmise at this point you have narrowed down where your problems lie. Before the pilot adjustments I had to rev the engine enough to take off, Now I can just easy the clutch to take off,it was too lean runs off of choke much better after opening up pilot.Good luck

OK. It's been a while but I finally had some positive results: here's a brief rundown.

No amount of cleaning the carbs made any difference at all.

I reset everything to stock, and then replaced the pilot jets with the next size up.

Then I set the idle mixtures by various methods again, finally ending up using the Color Tune to set the mixture to orange (too rich).

When set like this, the bike ran better when warmed up, but still took too long to warm up and (here's where it gets interesting) coughed off idle if driven off with the choke on anything but full. It would continue to cough for a while unless the choke was on full even after the point where the engine would stall if idled at that choke setting.

So, to me this was a clear indication that the needle was too lean. The interesting thing is that this coughing behavior didn't happen at leaner idle mixtures. It just felt powerless off idle in that case. So here using a too rich idle mixture severed as a diagnostic method.

Anyway, I pulled the carbs again and put one shim back on the needles (0.5mm), and set the idle mixtures back to just to the blue side of orange with the color tune.

Now the bike is running well, it seems to have enough power off idle and at the low end without feeling like it's bogging down. The warm up/choke behavior is now more in line with my other bike.

I suspect that adding another shim back might give a little more power at the low end--but it's so close to perfect right now I'm not going to mess with it.

Mileage is around 33 MPG in the twisties.

Conclusions:

Probably could have gone up two sizes on the pilots and 1mm worth of needle shims.

The important take-away here, I think is that you may be able to determine conclusively that your needle is too lean by setting the idle mixture too rich. If the carbs cough a lot and it runs better with the enricher on, then you may need to shim the needles. Much more of a solid symptom than the vague 'feels flat' symptom had at leaner idle mixtures.