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Have you checked for a blown PV? You really need to rule that out. Your jetting doesn't sound that fat for the carb, although a 750DP isn't ideal for your car. A reduction in jetting might help the problem but I think its a partial bandaid for whatever else might be wrong. Might you have 50cc accelerator pumps on it? (instead of 30's, at least on the primary)
Do you drive with a reasonably steady foot?--DP's can kill MPG if the driver is a constant pedal modulator!!!
Thats a pretty big cam if you don't have say at least 9:1 compression to match.
Is your 4-6 mpg number accurate or might it really be 6-8? Is your odometer accurate or does it read 'slow'?

just random thoughts



I have 30's all the way around. I normally don't have a steady foot but I cruised a full tank out on the highway and the mpg didnt change.

The compression figures out to 9.3
My speedo is slow by 10mph never thought of that