need help - MAF problem?

[aaron-san]

i have a 76 280z. when i bought it, it had an adjustable risistor on the wire that i believe tells the computer how much fuel to send. but it was broke and would flip out sometimes so i found what ohm it was at when it was running good and just put a resistor in place. me and my ad looked at it and figured the mass air flow sensor was probably messed up, plus it looked like it had been taken apart before. my car was running fine though, just rich, until recently it looses power over 4000 rpm, badly in 3rd and 4th gear. my theory is its sensing too much air and sending too much fuel, because when im over 4000 rpms and step on it it backfires alot and boggs down and actually starts slowing down. and that would explain why it does it worse in 3rd and 4th gear because im going faster so theres more air for the engine. my friend was driving behind me one day and i did it and he said it actually shot a pretty big flame whn it started slowing down. so does my theory sound reasonable or could it be something else. sorry this is so long just want to let you know all the facts. if anybody knows anything id greatly appreciate it.