I bought a small section of .5mm Nitrile diaphram rubber from REGLIN in Melbourne .This stuff isn't cheap ...but I now have enough to last me . I also got a bit of .3mm for carby diaphrams .
I dissasembled the Lucas unit to find the original diaphram as hard as a rock . No wonder it wasn't moving. You carefully use a screwdriver and lever up the edges ..Be patient and it will be OK .
There are variations in the lever/rod that actually moves the plate around . The 54 dated one I rebuilt has a arm . But a 56 dated one has a spring type arrangement .
To test the unit , I have a neat tool called a MITYVAC , it developes a measured vacuum . But you can use a syringe from a chemist and plastic tubing from Bunnings and a few T joins for a gauge if you want to .
The numbers stamped on the unit mean:
7 18 12
7 inches of vacuum is when it begins to move ....18 degrees is the max advance at 12" of vacuum .
It's important to have this unit working in order for the motor to develope its low rev horsepower .
Theroretically, the advance weights inside the dissy don't do anything unitil about 1200 rpm , so, if the vacuum unit isn't working, then the engine only has the static advance to use, hence it will be rather gutless at low revs .
The hex nut is soldered onto the housing unit and it tends to come loose , so I had to solder it back on . Also , the screw in end of the hex unit that holds the pipe from the carby , tends to leak , I had to use plumbers teflon tape on the thread to effect a good seal .
One thing when assembling the unit, the arm that attaches to the dissy plate, has to be in the same position as it was originally , otherwise the pin on the arm end will not align with the hole in the plate . Once the diaphram is sealed up, you cannot change the arm position ..BEWARE !
After its all together and in the dissy , apply vacuum to the carby end of the pipe with your syringe and the dissy plate should move around . It should start to move at 7" of vacuum. And, importantly, it should hold the plate there , if the plate slowly moves back, you have a leak somewhere that has to be fixed
Master
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