79 kz1000 initial throttle response

Hello, I'm getting poor throttle response at low rpm, and I have to really ride the clutch to start moving. I believe plugs are carbon fouling as well. It's a 79 kz1000a3a, vm28ss, 4-1 kerker, uni pods, 15 pilots, 110 mains, air screws at 1 1/8 turns out. Float levels and accel pump are good, I think, and they're synced at 22cm Hg.

Also, as far as the vacuum nozzles on the carb bodies...#1 doesn't have one, #3 goes to petcock switch, ok. #2&4 have always been capped, but are they supposed to be open vents?

I'm having another issue, but I'll post that in electrical. Thanks to all. Elliot

Post edited by: elwood, at: 2007/09/07 21:12

Elwood, are those vents or vacuum ports? If vacuum ports they will make it run like you describe.

I think at least on the #3 it serves as a vacuum to the petcock switch. Something tells me #2&4 should be open to vent, but maybe when the airbox was removed they got capped instead. I'll pull the caps and take it for a spin to see what happens.

elwood wrote:

... #3 it serves as a vacuum to the petcock... #2&4 should be open to vent....

Confirming your thoughts:

Yes - tube from #3 serves as vacuum to petcock, and hoses from #2&4 are open to vent.

The posted diagram doesn't show the clip at the end of hose 45 which helps secure the hose to the petcock fitting.

2 and 4 are vents as noted. These vents are brass fittings and if you noticed, attach to the adjacent carb via a rubber hose. On both the 1 and 2 carbs, the external vent leads to internal passageways in the carb bodies and to holes in the top of the bowl chamber. This vent allows the bowls to breathe and not get vacuum locked. If vacuum lock occurs, the floats don't work as they should. Gas will either not flow or will not stop flowing. Most folks put hoses on the vents and route the hoses over the swingarm. In the event he bike tips over, gas will pout out the vent fittings which, as you recall, are connected directly to the float bowls. Having gas pour on your hot engine with your leg possibly trapped beneath doesn't seem like a good idea; thus the hoses, routing gas away. The main thing is that the vents not be obstructed or plugged. The fitting on the #3 carb is a VACUUM fitting. It is connected to a passageway at the bottom of the #3 carb venturi. The vacuum is used for actuating a petcock. If not used, it MUST be plugged or the extra air will mess up your bike's idle. See the VM Carb Connections link on our website under "wg's Tech Stuff Index" for pics and further explanation.

Wow! I removed the caps and ran the vent tubes, and it runs much smoother. Can't believe I've suffered this long. I haven't repeated vacuum sync. It still lacks power until you open it up more than about 1/4 throttle. It has that baah sound, it doesn't sound tight, and although the backfires have decreased, they haven't stopped.

I've had the bike a little over ten years, and the #3 cylinder has always been unreliable. The plug is always the first to foul, the exhaust pipe is always a little cooler, and sometimes I lose #3 all together. I've always thought it was an electrical demon, but just in case it could be carb related I thought I'd include it here.

Thanks for the help to date, any other input would be greatly appreciated. Elliot