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Accelerator pump ball valve blockage - Fuel System/Carbs - The Lotus Forums #ForTheOwners Jump to content

Accelerator pump ball valve blockage

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While waiting for parts to arrive to reset my dizzy I had a closer look at my re-built carb while it was out of the car. I used a rebuilt kit from SJ and also replaced the idle jets, main jets and accelerator pump nozzles (Eurocarb sourced). So far so good. So sitting and waiting for parts I decided to test the accelerator pumps and sure enough discovered that they were only working on one carb. Strip and evaluation revelead that culprit was the non-serviceable one-way valve at the bottom of the carb atop the pump diaphragm. This is a turbo specific issue. There are 2 one-way valves in the bottom plate: one is part of a removable screw and shuts while the pump is triggered thus ensuring the fuel goes up and out through the accelerator jets eliminating backflow. The other (non serviceable part 34 in the page manual) valve shuts the pump reservoir fuel intake when the turbo kicks in and pressurizes the carbs. The only way for fuel to get into the pump chamber below is through this valve...

mine had an issue. I could hear the ball rattle around in it so had had no choice but to drill the press-fit top out to get to the bottom of it. Out comes the valve ball but no sight of the spring... where had it gone? Well, it turns out it was stuck in compressed state (!) and cacked in old fuel residue. Careful probing with a needle pried it loose and popped it open. More cleaning got the valve reset, the spring was in surprisingly good condition, no rust, just caked in light brown residue. With the cleaning all done, I had to remake a new press fit top using a piece of brass repurposed from the old pump diaphragm piston, size and shape it correctly and press it back into it. Worked. The only way to dry test this valve is to use a needle, insert it into the centre of the keyhole opening and carefully press down. There should be about 1.5 to 2mm motion on the ball and the ball should always come back to top stop. There should be no rattling of the ball when you shake it. Always check that on both carb bottom plates and with these valves. Mind you, It's the only way for fuel to get to the pump. If that valve is blocked or partially blocked like on mine, there are issues. Getting this fixed might just have cured my stumble off idle (I'll update you on that in my other pending thread)


Correctly working valve & Rebuilt valve



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Forgot to add that I had full accelerator jet spray function on all jets after fixing this :-) so when you rebuild or service your carbs on Turbo cars, always check those valves in the process...

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