Fuel pump test
Low fuel pressure often has this symptom: Engine idles fine, but when you "give it the foot" it runs poorly, backfires or runs slows down. High fuel pressure can cause poor fuel economy or flooding (raw fuel running down throttles).

1. Pressure test: Use a tee line to tap your pressure gauge into the fuel line near the carb. Pressure with engine running should be 2.4 psi or slightly more

- If the pressure is significantly higher with the stock A12 fuel pump, replace the pump

- If the pressure is low, replace the pump

2. Volume test: disconnect line from carb, put in quart/liter container. Start engine and run at 1,000 rpm for one minute (use a stopwatch). 450 cc or more should be pumped

Caution: don't let the gas spill!

If this pumps less than 450 ccs, try without the fuel filter:

- If it improves, replace the fuel filter
- If it doesn't the pump is likely bad. It could also be a clogged line, but this isn't too common unless the car has been sitting for years without running

reference