TOPIC:

KZ1000P with BS34CV carbs, stock everything.

I've had my carbs out at least a a dozen times trying to get rid of this flat spot off idle.

Here are the symptoms:

Bike feels a little powerless just off idle, with most of the torque coming in at 3k RPM.

The powerless feeling is most noticeable after decelerating (with engine braking) to a near stop and then taking off again (as at stop-light that turns green just in time).

I've gone both rich and lean on the idle mixtures with no real effect (other than the usual symptoms of running rich or lean). I've also shimmed the needles with no effect.

It is a pretty subtle effect, so there are times I'll go on a short test ride and think it's gone, but later a longer ride reveals the problem again.

In fact, it's so subtle that I probably would have just gotten used to it if I didn't have another identical bike which always pulls hard from idle on up to 7-8K.

Does anyone have any ideas? I've sync'd everything a hundred times. The plugs, of course, look perfect. Ignition is good. It's not missing, stumbling, surging or bogging in any obvious way. There's just a lack of power off idle.

Different springs weights on the carb slides? or some kind of vacuum leak. If it's worse after being on the over run are the slides somehow sticky after being closed for that period. Certainly a strange one. You could always try swapping the carbs between the bikes to see if the problem persists or follows the carbs.

redhawk4 wrote: Different springs weights on the carb slides? or some kind of vacuum leak. If it's worse after being on the over run are the slides somehow sticky after being closed for that period. Certainly a strange one. You could always try swapping the carbs between the bikes to see if the problem persists or follows the carbs.

Hmm. I suppose a difference in the springs is a possibility, but I'd think if that were the case then shimming the needles would have helped. Definitely not a vacuum leak--all new rubber, been over it a dozen times. As to the slides sticking. I thought that might be the case, so I lubed them with teflon dry lube. They move smoothly when off the bike anyway.

Yeah. I could swap the carbs, but that wouldn't really help me narrow down the issue any further. Both bikes are tuned up, valves adjusted, timing correct, advance mech lubed, coil modded etc.

The "off idle" stumble can be a needle position issue.

When mine was doing that, it was some very thin slits (almost invisible) in the carb piston rubbers. That makes the piston rise a little slower and starves for fuel.

jackleberry wrote: KZ1000P with BS34CV carbs, stock everything.

Aftermarket pipe?

Make sure you have the right pilot jets. Some of the bike's got lean jets for emission control.

How far open are the pilot screws? Have you set them to achieve the highest idle? If the bike hesitates then it's likely it's a little lean. I'd try 3 turns open at minimum.

What kind of voltage do you get at the coils? Should be at least 11 volts. What about the ignition wires and plug caps? If they are original you may want to update them as part of maintenance.

I concur with Nessism, I had my carbs rebuilt by wgcarbs, pilot needle setting at 1.5 turns out , bs34cv carbs, GPZ 750. i noticed I needed about quarter throttle before it would accelerate, sync carbs and reset pilot jet setting. After opening up to 2.5 turns on pilot I had much improved off of idle, and cruising speed at partial throttle was much improved no more surging at freeway cruising speed. Carbs were rebuilt with pipe and pods in mind as far as jetting.

bountyhunter wrote: The "off idle" stumble can be a needle position issue.

When mine was doing that, it was some very thin slits (almost invisible) in the carb piston rubbers. That makes the piston rise a little slower and starves for fuel.

Rubbers are intact.

bountyhunter wrote:

jackleberry wrote: KZ1000P with BS34CV carbs, stock everything.

Aftermarket pipe?

Make sure you have the right pilot jets. Some of the bike's got lean jets for emission control.

Stock everything. Including pipes, airbox, jets, needles. I do have the next size larger pilot jets to try, but but since I'm not at the limit of the mixture screw adjustment range, I doubt it would make a difference.

Nessism wrote: How far open are the pilot screws? Have you set them to achieve the highest idle? If the bike hesitates then it's likely it's a little lean. I'd try 3 turns open at minimum.

What kind of voltage do you get at the coils? Should be at least 11 volts. What about the ignition wires and plug caps? If they are original you may want to update them as part of maintenance.

Pilot screws vary. Right now, set by highest vacuum, they're around 1.75 to 2.5.

I wouldn't say that what it's doing is hesitating. I've tried going richer too (maybe too rich?) but the problem never goes away.

Battery voltage minus 0.2Volts at the coils. New plugs, wires and caps.

What kind of air filter? Stock?

I'd set the pilot screws to 3 turns open and see if that helps.

Nessism wrote: What kind of air filter? Stock?

I'd set the pilot screws to 3 turns open and see if that helps.

Yes, stock air filter. Stock EVERYTHING.

I have had the pilots at 2 (all) 2.5 (all) and 2.25 - 3.25 (mixed, set with Colortune) with no difference as far as the flat spot goes (changes the amount of time spent on 'choke' and the stability of the idle speed after long runs though). If I set them all to 3 turns, then a couple would be too rich (orange flame on Colortune).