The diaphragm failed on my 1959 Dexta while using it. The revs just kept going higher and higher even with the throttle shut to idle. I removed the diaphragm and found a massive split in the old leather. I ordered a new one from Agriline Products, cleaned out all the old muck and debris, applied some oil to the linkages and refitted the diaphragm.
Now I can't rev the engine past 1,200 RPM and the engine cuts out when I return it to idle. I have tried unscrewing the stop screw which allows the throttle to open more but it only increased the revs to around 1400. The new diaphragm didn't have a pip notch in the aluminium outer ring but I assume this is to stop the diaphragm from twisting during assembly and doesn't affect the operation? I made sure the leather was central and hadn't twisted before reassembly. Has anyone else used a diaphragm from Agriline Products with success?
mybe with the diafram fixed it means something eles is not working propley,
have you cleaned out the air bath filter gauge and the little gauge filter on the pump
, also mybe fuel tank filter may be blocked, just thinking outside the box
Yes cleaned the little round gauze filter on the side of the pump. Air filter is clean. New Fuel filter, new lift pump, new fuel tank tap and pipe from tap to pump. Fresh diesel and tank is spotless inside.
Update - I removed the air cleaner pipe to manifold, got just 200 rpm more. I removed the inlet manifold and cleaned out all the carbon from it and checked that the butterfly is opening fully. I now have 1600 RPM MAX but this is still too slow. I disconnected the vacuum pipe going to the diaphragm and started the engine and it revved to 2600. I tested the diaphragm as per the workshop manual by operating the cut out and checking it holds vacuum.
My thoughts are that either the vacuum spring is too weak or the leather diaphragm is not stretching or needs stretching? Has anyone else had trouble getting maximum RPM?
this really is a puzzler , when you took off the oil bath filter did you get the wire gauze
inside compleatly clean, some even boil it to get the oily gunk out of the wire mesh
this can restrict the revs big time, if this is all good then it must as you say something to
do with diafram ect
Skyblue my air cleaner is new and shiny with no gunk to block it
I think I may have found the problem. I removed the new diaphragm and compared it to the old one. The movement is huge compared to the old one.
This must mean it can pull the fuel rail shaft twice the distance inside the pump to cut the fuel quicker?
