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,

 

 

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Welcome to the forum. 

Removing all those vacuum lines for efi to work to run SUs that only need a couple would be a challenge. The vacuum advace nipple on the front carb comes to mind for me. Then the '77 carbon canister and using the '77 fuel tank. There's a lot to do I've read. I have a '77 and want to put a spare set of SUs on there myself but it runs good so I'm not able to open that can of worms right now.

Anyway, here's a thread you might could read over and get that lightbulb in your head idea. Good luck with it and you'll get some replies, mostly questions I bet. 

 

4-5 psi fuel pressure may be too much pressure for the float valves. 3-3 1/2 psi is all the carbs need. I'm assuming the 5 psi occurs at higher RPMs.