If I let up on the gas, doing 60 or more mph, the car (70z with a 75 l28) backfires. I adjusted the carbs and this reduced, but did not eliminate, the problem. Suggestions?

Thanks.

Do you still have the ABV in place still? (anti-backfire valve) It allows fresh air into the system to prevent the backfires- when i put SU's on my 260, i removed mine, and get minor backfires whenever i decelerate, or use the engine to brake.

I try to think of it as the Z "burping" after chewing up some road:cool:

Jeremiah

Yes, there's an ABV.

Also, these backfires are powerful, almost as loud as a shotgun.

or maybe just one. you said you adjusted the carbs. backfires are from running to rich. lean out the carbs a little and make sure there balanced. also you might want to look into some new plugs

james

The timing being off a little could also contribute to the backfiring. If you haven't done it yet, a complete tune-up would be a good place to start. Plugs, points, condensor, timing check, check your plug wires, cap and rotor. If this fails then go for the carb adjustments, and check the ABV.