I have a '74 1.8 that was converted to a single Weber carb sometime in its past. I realize its not the best set up. Car is not driven a lot.
When starting out on a drive, it runs well enough when cold (stumbles and not smooth but I figure that's because of the single carb set up). When it is warmed up (not hot), It runs pretty well. After driving for 30-45 minutes and the engine is hot, when I back off the gas it backfires and pops and will not idle when stopped at an intersection or light.
Why does it do this only after the engine is hot after some driving?
Points, timing, plugs all seem to be good. Plugs are a little black after one of these backfire sessions, but are not wet or smell like gas.
The valves have not been adjusted for a LONG time. Could this be the cause of the backfire/idle problem?
any ideas? Thanks in advance for the replies.
Ed
Pittsburgh, PA

I had the same set up never could get it run clean so switched to dual carbs and 90% of the running and idle problems went away plus it seems like I have more hp and it sounds cool

I would adjust the valves. They could be running tight. Go from there