Stumble @ 2500 rpm

I have a 77 KZ1000 with 12,000 miles on it, the bike has k&n pods on it and a mac 4 into 1 with a short glasspack instead of the mac baffle and the stock non accelerator pump carbs. i have 120 mains, the needle in the stock setting and 20 pilots in it. when in traffic the bike seems to have a slight dead spot right off idle and just loafing along it sputters at about 2000 to 3000 rpms, somewhere in that area. if you rail it open, it runs great and if you generally run it hard its fine, just going to work in traffic it gets to be annoying. i have the pilot screws out about a turn and a quarter and have tried them everywhere from a turn and a half out to half out, and tried 22.5 pilots and the stock 17.5 pilots. the 22.5 and 20 had similar results, the 17.5 pilots it wouldnt even harldey run. the carbs are synced and there doesnt seem to be any air leaks and the floats are set to 1 inch. the carbs are very clean, i had them off again yesterday. Any thoughts would be appreciated, i dont ride this bike much due to this problem and its not gonna sit out there takin up space, thanks guys.

If its just loafing along with small amounts of throttle input at that rpm it is the mixture screws, no matter what pilot you put in it.

Turn them out 1 at a time. Listening for the engine start to stumble, then turn that screw back in just until the idle comes back up/smooths out. All the misture screws should stumble around the same number of turns out (give or take 1/4 turn or so). If not, then you most likely have air intrusion from somewhere.

Check to make sure you have really excellent spark, and a vacuum syncronization would help alot.

Also be sure to set your dwell with some good feeler guages, or a meter, and set your points/timing with a gun - static timing is crap at best.

Good luck.

thanks for the reply, i will try the mixture screw business again how you said and see what happens. the carbs are vacuum synced and i will be doing them again if i ever get it to run right. the timing is spot on with a timing light and it has a dyna and 3 ohm coils and the spark seems pretty hot. thanks.

What is your compression like? New? ...or worn out old stuff?

Sometimes it helps alot to advance the initial timing a little (2-3 degrees) to restore some of your old girls bottom end power delivery.

Peace.

If not already done, would also assure that the timing advancer is functioning properly. By watching it under a strobe-type timing light and seeing it quickly move back and forth as rpm is varied by blipping the throttle. The advancer may require lubing, or both cleaning and lubing.

Meanwhile, Boo on me for suggesting that the carb pilot circuits are still imperfect regardless of the reported cleaning.

Oem carb pilot circuit looks like this:



May adapt the following pilot circuit cleaning method (illustrated with side-located pilot screw) to use on carb with bottom-located pilot mixture screw:



Wear eye protection!

Good Fortune!

"Jet Needle in the Stock position"
What does it do if you put it up a clip/ shim it? There is so many "Pod" threads, I think everyone of them ends up with the needle raised at least 1 notch/ shim. Have you tried this?

55fbomb wrote: I have a 77 KZ1000 with 12,000 miles on it, the bike has k&n pods on it and a mac 4 into 1 with a short glasspack instead of the mac baffle and the stock non accelerator pump carbs. i have 120 mains, the needle in the stock setting and 20 pilots in it. when in traffic the bike seems to have a slight dead spot right off idle and just loafing along it sputters at about 2000 to 3000 rpms, somewhere in that area. if you rail it open, it runs great and if you generally run it hard its fine, just going to work in traffic it gets to be annoying. i have the pilot screws out about a turn and a quarter and have tried them everywhere from a turn and a half out to half out, and tried 22.5 pilots and the stock 17.5 pilots. the 22.5 and 20 had similar results, the 17.5 pilots it wouldnt even harldey run. the carbs are synced and there doesnt seem to be any air leaks and the floats are set to 1 inch. the carbs are very clean, i had them off again yesterday. Any thoughts would be appreciated, i dont ride this bike much due to this problem and its not gonna sit out there takin up space, thanks guys.

Put the #20 pilots back in and lift the needle up one clip position. That's one clip position more, down from the top of the needle from where you are now.

Eg... Currently 3rd groove. Move to 4th. Then do a really good carb synch. [That advice presupposes that your fuel levels, valve lash and ignition timing are correct]

You're at the transition point where it's just coming on the needle. Pilot circuit, slide cut away & clip position all influence that point. It's the trickiest spot to nail down silky smooth once you remove the air box and bolt on a pipe. It can be more so with 30 year old carbs with worn parts. Give it a whirl before you do anything else and see...

A lot of times what happens is guys will get it near cured by dumping in too much fuel via the fuel mixture screws [underneath front of carbs]. Then the plugs turn sooty and it idles poorly on hot days.

This stuff passing for gasoline these days has changed the game a bit. I'm finding more situations where I have to set a richer clip position than I used to run.

Thanks everyone. the advance unit works correctly, i cleaned and lubed it and verified that it worked with a timing light. Im not about to say the pilot circuits are perfect but they flow carb cleaner everywhere it should go so i think they are ok, i cleaned the carbs and then cleaned em again, then i thought they were good to go so i cleaned em one more time to be sure lol. i believe what is happening is what cavanaughracing is describing because its worse on hot days and its not as bad when the bike isnt fully warmed up. i took tek9ines advice and it seems better, now i think i will take the rest of your advice and lift the needles one clip position and give that a run. i did find today that i had a drip of fuel hanging off the mixture screw for the #2 carb so i will be going through them again when i adjust the needles, thanks again everyone.

well, i tore everything back down and cleaned everything and reset the floats and made sure all passages are clean. the 20 pilots are in and about 1 turn outon the mixture screws, they still need fine tuning. i need to resync the carbs again too but so far it seems better. it felt like it was loading up at idle and the plugs were black so i cleaned the plugs and opened up the gap a little. but finally i think we are getting somewhere, thanks guys, i will let you all know as things shape up.

Well, finally got out this weekend and put about 100 miles on er this weekend and ran perfect. . . . . . . until i got back into town and got stuck in traffic. Is anyone here running stock pilots with pods? i have the 20s in it still at about .75 turns out and it still fat and loading up at idle it seems. if i get stuck in traffic it sputters once i get moving and belches out a bit of grey smoke when i first crack it open, then it clears up and is fine until i get stuck in traffic again. should i go back to the stock 17.5 pilots?

55fbomb wrote: Well, finally got out this weekend and put about 100 miles on er this weekend and ran perfect. . . . . . . until i got back into town and got stuck in traffic. Is anyone here running stock pilots with pods? i have the 20s in it still at about .75 turns out and it still fat and loading up at idle it seems. if i get stuck in traffic it sputters once i get moving and belches out a bit of grey smoke when i first crack it open, then it clears up and is fine until i get stuck in traffic again. should i go back to the stock 17.5 pilots?

have the 20s in it still at about .75 turns out --- perhaps pilot circuit is too rich. Side located pilot air screws should imo be set about 1.25~1.5 turns out from lightly seated.

If not already done, would also verify correct fuel level by performing the clear tube test.
A too high fuel level may result in an excessively rich mixture even in an otherwise perfect carb.

Reported issue can also result from overheating due to incorrect ignition timing or advancer function, or too tight valve clearances, or weak spark for whatever reason.

Good Fortune!

I also think that the pilots are rich but i cant figure out why, surely i shouldnt be using stock pilots with pods and a pretty much open 4 into 1? my carbs have the pilot screws in the float bowl area. i have set the floats, twice. is there a write up on this clear tube test? i looked around a bit but all i could find was people mentioning it but not how to do it. It doesnt seem to get overly warm, all my bikes are air cooled 4s and this one gets no warmer than the others. valve clearances should still be OK. i took the advance unit out and cleaned and oiled it and the spark should be fine, new plugs and caps, new wires and 3 ohm coils, and a new battery. timing is dead on with a timing light. the stumble seems to have moved to lower rpms now though, like right off idle. thanks guys.