Accelerator Pump

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Ray
Posts: 19
Joined: Sat Feb 22, 2020 1:30 pm

Accelerator Pump

Post by Ray » Fri May 29, 2020 11:35 am

My P3 75 Carburettor is a 30 PAAI_2
Droplets of fuel can be seen exiting the nozzles without touching the accelerator. Does anyone know the most likely cause of that? I would replace the accelerator pump complete but I have not been able to find one. Regards, Ray

Ray
Posts: 19
Joined: Sat Feb 22, 2020 1:30 pm

Re: Accelerator Pump

Post by Ray » Tue Jun 09, 2020 2:39 pm

I have disconnected the linkage to the accelerator pump but droplets are still exiting the nozzles when the engine is running.
The float bowl is full to the brim but the float valve is working OK. (new)
I assume the bowl is being fed by some alternative path.
Does anyone know how that might happen ?
Thanks in advance
Ray

TonyG
Posts: 128
Joined: Mon Sep 07, 2015 4:38 pm

Re: Accelerator Pump

Post by TonyG » Tue Jun 09, 2020 6:45 pm

Pretty amazing if your car is making its own petrol! However, I think it’s safe to assume that the fuel is coming from the tank via the float bowl. I do not have this type of carb on any of my cars, but If the float chamber is full to the brim, perhaps the valve is being forced open by the pressure of the pump and, in turn, pressurising the delivery of petrol through the carb. Hence the droplets of fuel you see. So, the question is, have you recently fitted a new fuel pump or modified the feed in some way? If you have an electric pump I seem to recall it needs to be low pressure of about 3-5psi and it is possible to fit a pressure regulator in the fuel line to achieve this. I used to have an Austin Healey that used to overflow from the float chambers on tick over because the pump pressure was too great for the valves.

Just a thought.

Tony.
Tony Gilbert

P1 12 Tourer
P2 12 6 Light Saloon
Discovery 3
Discovery Sport

Ray
Posts: 19
Joined: Sat Feb 22, 2020 1:30 pm

Re: Accelerator Pump

Post by Ray » Thu Jun 18, 2020 7:44 pm

I think the fuel level in the bowl, being full to the brim, was a one of.
It is now stopping at 0.71 inch from the brim, which seems too low.
Anyway, I removed the accelerator pump and tried blowing, using a short tube, back into the outlet. It was free to flow. I think this means that the ball is not seating properly.
I found that the stem of the diaphragm assembly is holding the ball off its seat. That is, no back flow when diaphragm assembly/stem is removed.
Does anyone know if this is normal ?
Regards, Ray

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