Possibly the advance isn't functioning. Most likely the vacuum advance, I
would think. Check the hose first, and then the diaphragm would be your
next suspect. If you disconnect the line at the carb end and suck on it,
you should be able to see the distributor plate move (that is if you
remembered to remove the distributor cap). If it doesn't, and you get a
mouthful of funky tasting air and hear a whistling sound, the diaphragm
is toast. I'm afraid the blighter is a little pricey, too. Check the
manual for instructions on disassembly. Good luck.
Robert Sexson had this to say:
> Today I have been trying to tune my 74.5 B. It will not run smouth when
>the timing is set at 10 btdc, increace the timing to 20 degrees and it will
>smouth out. Has anyone had this problem before?
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'66 MGB GHN3L76149
If you're near Mountain View, CA,
it's the red one with the silver bootlid.