VM28 Pump Plunger

Is the weight and check ball installed in all the bowls. Possibly the oring that seals the ball and weight slipped out of place.

Mikaw wrote: Is the weight and check ball installed in all the bowls. Possibly the oring that seals the ball and weight slipped out of place.

Ball, then weight, then clip holding them into the hole in the float bowl.

The spray nozzle has an O-ring but it's not big enough to seal against the passage in the float bowl. Honestly though, I would think the float bowl gasket would keep fuel inside but NO. I'm missing something (obviously.)

Is there any chance the spray nozzles are plugged and the fuel doesn't have anywhere to go?

Nessism wrote:

Mikaw wrote: Is the weight and check ball installed in all the bowls. Possibly the oring that seals the ball and weight slipped out of place.

Ball, then weight, then clip holding them into the hole in the float bowl.

The spray nozzle has an O-ring but it's not big enough to seal against the passage in the float bowl. Honestly though, I would think the float bowl gasket would keep fuel inside but NO. I'm missing something (obviously.)

Correct im sorry the spray nozzle O-Ring. I heard the right size is hard to get. I got mine in the Keyster kit and havent noticed any issues. DOHC has a good point.

The nozzles are open.

I put a second O-ring in, around the first small one and it's better, but still leaks on 3/4 bowls. I'm getting a nice spray on 3/4, and pretty sure the last one not spraying is because so much fluid is leaking. Only thing I can think of is that I need a much fatter O-ring than what I've got now, and what come on the carbs when I received them. The O-ring has to be fatter than the float bowl gasket thickness so it's got room to crush.

I gave up for today but will look at it again tomorrow. This one's got me flumoxed. I wonder if the float bowls are all warped?

Not sure this will help because I do not know the size of the O-ring.

Almost certain the problem is the O-ring. I put a small straight edge across the gasket surface and the O-ring sits below this surface which means it can't seal against the pump feed through the float bowl. Going to have to order some small but fat O-rings. Z1 suggests the size is 2.7mm x 1.8mm which sounds right. McMaster Carr has 2.8 x 1.9 which should be close enough.

Nessism wrote: Almost certain the problem is the O-ring. I put a small straight edge across the gasket surface and the O-ring sits below this surface which means it can't seal against the pump feed through the float bowl. Going to have to order some small but fat O-rings. Z1 suggests the size is 2.7mm x 1.8mm which sounds right. McMaster Carr has 2.8 x 1.9 which should be close enough.

Sounds like a good choice. Good luck.

I used a 2mm cross section by 3mm inside diameter., also been scrutinizing the carbs and manuals and they are the same as the Thou A3a models and probably others of the same time.

Installed the 2x3 O-rings and they look better, although they still don't sit above the gasket by much. Fingers crossed.

Got some photos of the pump linkage and the frankinknod. Getting close.

BTW, how is the pump supposed to be adjusted?

Another shot of the KZ550 knob. I drilled the hole in the back on a lathe then used a punch to separate the knob from the threaded rod. Then the knob was pressed in place in the VM28 rod after slathering 3M DP420 epoxy on the parts. Good fun.

Between the two lines needs to be 10.7 - 10.9 mm, once i set mine up there i made a threaded adjuster that is the same length as exposed thread and original adjuster and put that on instead, so now my adjuster is flush with the bottom of the rod at correct adjustment.