Onta_Z

Long story short: bought a 77 280z from some guy who tried to convert efi to carburetor because of EFI problems he apparently was having. He installed an ignition module from a ford ranchero (luckily it somehow worked)however, he Never got the car running. I bought it, turns out the gas tank was completely fried. Bought a new/used gas tank, installed, car runs good. Had a good friend come over and tune the carbs, car ran good still. Went to take it out on a longer than usual cruise, and the car after hitting 45-60 mph slowly would loose power. I have backfire coming out of the exhaust upon de acceleration. Spark plugs were wet and black. I leaned out the carbs a bit to resolve the issue, i tore out the half arse ignition module and replaced it with the GM HEI ignition module upgrade. Fuel pump has been replaced with K&N one from Z store, (fuel pressure checks out and ranges from 3.5-5 PSI). Does anyone have any recommendations on what to check out next? Maybe a clogged cat? Fuel tank clogged somewhere? Dizzy is bad? Thank you, Sent from my iPhone using Tapatalk