1963 Volkswagen Karmann Ghia

Engine Performance problem
1963 Volkswagen Karmann Ghia 4 cyl Two Wheel Drive Manual

I get a very low vacumm reading, less than 5.
I checked compression, all cyl. Are over 100 lbs I cannot find any leaks in the intake manifold. Retighted the bolts I put my hand over the carb, almost lost my hand fromthe suction. Engine idles o.K. But under load it back fires. Vacumm does not advance.
I have run out of ideas
July 20, 2010.

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