vm28ss...can't get the accelerator pump to work

I have 2 choices for the pump float bowl...1 has the triangular extra diaphragm, 1 has this extra diaphragm section plugged. I am assuming that if I use the bowl with the triangle diapragm plugged I should be able to bench test the pump and see gas squirting out of the squirters, correct? And that the bowl that includes the triangle diaphragm needs to see engine vacuum before the accelerator pump will operate, correct?
Next possible problem...I have removed the tiny clips that hold the check ball and restrictor for cleaning and I have noticed that there is a nearly microscopic groove in the well for the clip. If you get the clip into the groove properly it allows the restrictor and check ball to rattle around in there quite a bit. Is this necessary for the accelerator pump to operate? It seems almost impossible to get the clips back into the groove. Those stupid little clips have been flying all over my shop and of course are then impossible to recapture.
Also, is the pump circuit even of any benefit? Can these carbs be tuned to operate adequately without the pump circuit?

Oh yeah, these are going on a '78 kz1000 with Andrews 2x cams and ported cylinder head...

Many people disable the pump and just rejet as necessary. They report the bike runs fine that way, and is more consistent.

Thanks. I was expecting the pump to be beneficial to throttle response, but it seems like no one can be bothered to get it working properly.

My 81 KZ650-CSR has VM24 carburetors w accelerator pump. The vacuum sensor is factory disabled --- the orifices for it are either plugged or not drilled. I installed a new K&L kit a few years ago. All of the little parts are present for each carb (balls, rods, & clips).

To test the accelerator pump the manual says to quickly operate the throttle pulley & check that fuel squirts from each nozzle without hitting the carb bore walls & the quantity ejected from each nozzle should be the same.

Bench testing: the amount of fuel ejected is dependent upon how vigorously the throttle pulley is actuated: slowly = small amount of fuel & quickly/vigorously = a good squirt.

Here's a cutaway diagram of the VM accelerator pump w vacuum sensor.

Is there anywhere to buy the tiny clips (part # 13 in the diagram) for the check balls besides buying the whole pump diaphragm kit to get just one?

The clips are NLA. The K&L AP kit includes the little parts. Other than the kit or eebbaay, as far as I know the clips aren't available anywhere. Spring clamp/clip (92037-1123) --- $1.99 & $5+ shipping. ouch .

Since your bike is a KZ1000 & it has had some performance stuff done to it, perhaps you should check further as to whether or not disabling the AP would be the thing to do. ??? I think the pump was added to address a lean condition under heavy throttle or something --->>> perhaps as a consequence of the lean jetting mandated by the EPA. ???

The AP is reportedly prone to clogs and difficult to keep perfectly clean.

As Martin suggested, would consider disabling the AP and compensate with non-AP jetting.

Good Fortune!

martin_csr wrote: ... I think the pump was added to address a lean condition under heavy throttle or something --->>> perhaps as a consequence of the lean jetting mandated by the EPA. ???

That's what I suspected as well.

Jetting richer for acceleration meant it was richer for moderate cruising. So to keep it lean for cruising, they jetted it lean and added the pump for acceleration only.

My buddy's ST ran so much better after he ditched the pump and rejetted.

It's more or less a waste of time getting the pumps working unless you ride year around. If the carbs sit more than a month what happens is the gas evaporates and the pumps will never pump any gas. I fought this on my KZ1000s, same thing happens on both of them, after sitting the pumps go dry and won't work. They just pump air. If gas finally works its way in and the pump more or less gets primed, it works fine, but I guess mine at least would never prime after sitting dry. The orifices never were clogged, just no gas would pump.