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MG MGA - Testing vacuum advance diaphragm

How can you test the vacuum advance on the distributor to ensure that the diaphragm is working and not damaged. I put a Mitivak tubing on the inlet nipple of the top of the vacuum unit and it did not hold a steady vacuum but leaked down fairly quickly. Is this OK?

Andy Preston

Andy, you could use a timing light and pull the vacuum line off while running and you should see the spark timing change. This may not show up a small leak though
A Pearse

There should be no vacuum leakage from the advance unit.
Cheers - Dave
David DuBois

This sounds terrible but I use my mouth to suck on the vacuum unit, after removing the vacuum line. I then hold the vacuum by placing my tongue on the inlet. There should be no leakage.
I warned you it was a bit odd, but it works and it is quick. I started working on cars over 50 years ago with a hammer and a pair of pliers and haven't progressed much.
On my MGA 1500 I set the valve clearances by feel, but invested in a set of feeler gauges when I bought my Twin Cam in 1964. Still had the fastest mga twin cam in the State of South Australia and hadn't even heard of a stroboscope.
I now do all my work on my modern car with a laptop computer.

M F Anderson

Hi Mick - it's not just me then - I have always used to suck it and see method too - cheers Cam
Cam Cunningham

This thread was discussed on 05/02/2009

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