There are three different pumps,one for the AVS and two for the AFB.AVS is larger in diameter,AFB uses two different length pumps,AVS on right,AFB's on left.The AFB pumps have a check valve in the bottom of the pump,the AVS does not.If you have the correct pump,the pump length adjustment is correct,the connecting link is not installed backwards,the check valve in the driver side bowl to pump well is good,correct fuel level and the needle under the discharge nozzle is in place you should have no problem regardless of what pump you use if it is in good condition.I have been playing with these thing for 40 + years and can honestly say I have never had a pump problem if all the above are correct.I have went as far as soaking dried up leather pumps in oil and reusing them with no problems.