Off idle mid range crapping

Stock `81 KZ1000. I've had the carbs apart and am sure the pilot circuit is clear. The one thing I haven't taken apart is the slide diaphragms and driven out the needle jets with a wooden dowel. Am I on the right track to cure this mid range crapping?

I've tried to choke each carb "by hand" as I drive to find the culprit. One seem to be lean but things happen so fast it's hard to tell.

Not sure what the problem is that is being asked about. Not sure what carbs are being asked about. Not sure what jetting is in the carbs. Not sure what the airbox or pipes are on the bike. Just a little info would sure help.

Sorry, I thought "stock" covered it. Guess not.

1981 KZ1000, BS34 carbs with original jets, airbox (removed for testing)and stock pipes.
The "stumble" at about 1,800 RPM to about 2,500. All I've read indicates the pilot circuit is at fault.

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. I'm ready to try them again in hopes I "jarred" something. Any advice?

Post edited by: tubbytwo, at: 2007/12/31 12:58

The KZ1000P had VM28 pumper carbs. Wasn't sure what bike was being discussed since model wasn't mentioned. The BS34s on your bike are sensitive to changes to the airbox. Since you don't have one on the bike, it won't run right... hard to start, lean and won't pull over 7K rpm or so. Suggest you free the mixture screws that are stuck and seat them 1 1/2 turns out from lightly seated and I would go ahead and replace the pilot jets as well. Cleaning pilot jets can be a frustrating project as the holes are so small, even if they seem to be unobstructed, old crud can cause poor fuel dispersion. Replace the orings on the all the pilot mixture screws.

Thanks for your answers. The two mixture screws are now broken. The top eighth inch broke off both. The two that were free were exactly 1½ turns out so I'm going to leave them as they are. The main were 130, so someone has been in there.

I had a devil of a time getting the carbs and airbox out. Those rubber boots were hard as rocks. (Wonder if brake fluid would soften them) Same with my 650, and the only reason for pods. It, by the way runs great, although different carbs.

The chain was dry and rusted so I'm in need of a chain/sprockets. I'm shocked at the prices. This $400 bike is getting expensive!

With 130 jets and two .020 shims (small brass washers) in each carb, and with pods I still had a slight stumble. I bought a 5-way "T" at Auto Zone (Dorman 47361)and connected all four carbs and the fuel shut off. This smoothed things out Problem solved. Well worth the $3.00



Post edited by: tubbytwo, at: 2008/01/20 00:29

tubbytwo wrote:

Sorry, I thought "stock" covered it. Guess not.

1981 KZ1000, BS34 carbs with original jets, airbox (removed for testing)and stock pipes.
The "stumble" at about 1,800 RPM to about 2,500. All I've read indicates the pilot circuit is at fault.

Not so sure. I had the same throttle stumble on mine between 2k and 3k RPM, and I kept going to richer pilot jets with small effect: then I moved the needle position one notch richer and had a huge improvement. You might try that and see.

The pilot system and the needle/main system both cross over in that region and the piston is starting to lift. If you can't go to another notch on the needle, try shimming it up a bit.

Post edited by: bountyhunter, at: 2008/01/21 14:37