Last fall I had a dynotune. the car ran great. after the winter it runs good until I get to 3500 rpm. it ran ruff after 3500 rpm. almost like it was starved for fuel. this is what I did: ran all gas out in tank thinking gas went bad....no change replaced fuel filter.... no change I cranked the fuel pump up to 9 psi and still no change I took the air filter off and played with the throttle. I saw it back fire from the carb. the air filter cover appeared to have fire marks on the inside above the carb. is it a timing issue/advance issue? dirty carb? advance not working? camshaft? what ya think?
What all have you done to your engine before the dyno and what numbers did it pull? Get a chance, open hood and run it till it misses in the dark, may find you a answer.
how many miles on that timing chain? may have jumped a tooth... check the timing with a timing light.
was it doing this before dyno tune ,if not go back to where you got it done and find out what they did, right about running after dark to see if plug wires shorting or bad cap or whatever,
I have an HEI, Edelbrock 4bbl and electric pump. timing chaing has less than 2000 miles, never did this before
im suspecting that the secondary fuel circut in the carb is pluged up. take the top off the carb. its easy to do. you can then look into the bowls. see if there is any debrie in the bowls. also sence it say the fuel could have dried up in a passage and clogged the secondarys.
backfire Most often a timing issue, but make sure the carb is right first. What kind of dizzy are you running?
It was running good when he parked it - after the winter it backfires only above 3500 rpm. He changed all the filters, boosted pump pressure to 9 psi and has replaced the fuel. That leaves a dirty carb, wires, plugs or a sticky intake valve.
