Engine Performance on Cold Start Concern

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mrhp

mrhp

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440 with electronic ignition, Mopar chrome box. Dual 500 cfm Performer carbs, no choke (Not needed here in SoCal). I take it out for a drive every 2 to 3 weeks. It has always run just perfect, even on cold starts. About 3 months ago when I fired it up cold it ran rough and when I would give it some gas to raise the idle it would pop back in the muffler. After I put it in gear and started to drive it would run fine after 2 to 3 minutes. Module is in spec and I took the ignition box over to Autozone as they have the complete test kit from back in the day. They let me use it and the box tested fine. Same thing the next couple of times. Then it was fine on the cold start for the next couple of times after that. Then yesterday it happened again - ran rough and popped back in the exhaust when I raised the idle. Went for a drive and after 2-3 min all was fine. Thoughts?
 
were those days colder on the rough start? Temp changes can affect the boxes.
 
The gasoline could be going south from little or non use. Plugs could be a bit south due to cold starts and heavy throttle. Not running the vehicle at temp can cause these issues.
 
The first time it happened it was colder and it had been raining a lot too. That's what led me to bench test the box. I always run and drive the car for a good 30-45 min whenever I start it up. Gas has been getting worse here too which I'm sure doesn't help. Every few tanks I put in a couple of gallons of 110 leaded racing fuel plus I've put in a couple ounces of that Sta-Bil 'anti-ethanol' additive recently to help offset the poor quality. I also put new needle/seat assemblies and accelerator pump in. Was thinking to put new plugs in too so I'll do that next. Thanks
 
Using NKG XR5 Spark Plugs. Don't remember: What should I gap them at?
Any other plug recommendation than these before I pick a set up?
 
Carb stuff was after as a preventative to make more 'ethanol safe'. Did notice crisper acceleration most likely to the new accelerator pump but no effect on the main concern.
 
Chrome box? Gap at .050

Plugs? Champs always worked for me.
 
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