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Start with a tune up. Spark plugs, wires, cap & rotor. & air filter.
Finish with rebuilding or getting the Qjet carb sent off and rebuilt correctly....then to go through all the obvious setups on timing/etc....need know the miles on the car before more suggestions....also about the driver train....tranny/rear diffy ratio...all these things on a for sure basis....old cars have lotsa hotrodding done over the years/decades...so all this need be proven to know for sure where to go....at 7.x mpg it's really poor, I would go for the Qjet along with the above tune up's....
Personally I would look at some things before I started tearing anything apart.
There are some basic questions I would look for.
Do you smell any fuel when you start the car, shut it off or while driving it?
How is the car performing?
Do you know what rear end is in the car?
Remove the air cleaner, do you see fuel stains on the intake. Carb leaking
Look under the rear of the car on the exhaust, do you see any brownish color stains? Fuel Tank leaking.
Inspect the area around the fuel pump for a leak.
Is there any smoke coming out of the car?
Pull the plugs and inspect them. See if you have fuel fouled plugs, carbon on the tips, brunt electrodes etc. Read the spark plugs, they will always tell a tale.
Eliminate the obvious first before you start pitching money out the window.