Backfire -- exhaust -- driver side

I fired my engine for the first time since putting on the aluminum heads; I have a backfire through the drivers side exhaust about every 3 seconds at any throttle position. Engine also does not idle down as well as before. No changes other than new heads. Same problem cold or hot. Fuel pressure 5 pounds at carb. Timing seems not to affect the problem.

?? float too high, bad valves/seals in carb,(carb is 3 years old, about 2 hours of run time in my driveway), ?? 5-7 induced spark (thought this would be an intake backfire), spark plug misfire, exhaust valve sticking open?

3 years ago new carb ran smooth right out of the box, no mods to floats or jets.

Chev 454, 9.5:1, Holley 750, Msd 6 box, Msd distributor, Comp cam 235 duration at 0.050, hydraulic lifters, 2" headers.

Jim

Could be you missed the lifter with the pushrod? Or adjustment of valves wrong? Crossed wires? Lots of possibilities.

I would check valve adjustment.

Well......... I found the problem; it is 'the nut behind the wheel' or wrench in this case. When I put the new heads on, I reversed the wires on #5 and #7.

Thanks for the responses and for tolerating a fool....

Jim

Don't be hard on yourself. You ain't exactly the only guy that ever did that.


Jim

we all get plug wires crossed every now and then.... its only a big dummy move if you mix up all 8 of em, 2 crossed no biggy, happens to the best of us... just be glad it was something easy to fix with no tear down

When I fired up my 454 for the first time over 10 years ago, I couldn't get it to run whatever I did. Huge backfires and massive flames out the carb. Tried all afternoon!!
Turned out I had wired the plugs as per Ford or Daimler V8, my only V8 experience up to then. When I made a phone call and found out Chevys were different, it started first turn of the key...
Chris