28mm Pumpers ?

I'm looking at some Mikuni 28mm accelerator pump carbs. and looking at the photos, it doesn't have the 3-screw Vacuum Sensor Cover mounted. Apparently it is missing ? Is it needed for the carbs. to operate ?

On those 28mm pumper carbs all are cast for the sensor but not operational. The 1980 ST I had was a bare open receptacle for the sensor but not completely milled or operational. No leaks there and no need to cover. I believe the FSM is where i found this detail. BTW, the pumper carbs are a useless PIA. it only dumps gas to avoid a lean idle circuit. the little check valves, clips and ball bearings are a PIA too. Find some regular bowls or non pumper carbs ard re jet IMHO.

R

Nothing is missing on those 28's.
The pumper float bowl is a common casting to both the 26mm and 28mm carbs however both diaphragms were only used on the 26mm ones .
On the 28's this diaphragm is not used so the casting in that area remains un machined and no cap fitted.

Now that I have that ruled out about the casting cap, I'm wondering if I'm just wasting time focusing on the pumpers whether something better for my engine build with a 1075 kit and possibly head and cam work ?

29 Smoothbore's are unaffordable but BS34's are ? Just not sure about a CV carb. as oppose to a slide type ?

Those 28 pumpers are the best of all the zed slide carbs.
If they are good condition at the right price I would snap them up.
It's the 26mm pumpers that are shite not the 28's.
Don't bother with CV's and 29 smoothies won't have any advantage and can be much harder to set up.

Agree but I'd like to see what we're talking about.
Steve