Troubleshooting my FE

[CompFi]

I have a 427 side oiler from Shelby engine, 496 CID. It came from Shelby with the Holley 80805 carb, which is the 4150 Ultra XP model rated at 950 cfm.
Then:
• In 2022 when I bought it, Billy Andrews of HRE sorted and tuned the car. The engine was simply a rocket. No issues whatsoever.
• The plan was for me to return the car to Billy in summer of 2023 after adding approximately 1000 miles and he would make any necessary adjustments to the tune.
• Sadly, Billy passed away last year. I am grateful for the opportunities to hang out with him in his shop. We laughed a lot, while I learned a lot. I miss him…

• I still have a lot to learn. I am willing to learn, or at least attempt anyway….
• The 2023 driving season started where we left off in 2022, no issues.
• But as Billy expected, the engine began to run rough in the middle of the driving season last year. I noticed some lag in 2nd gear around 2k rpm, where previously 2nd gear had been exceedingly responsive.
• I also noted rising operating temps, even just on a cruise of country roads. Sometimes hitting 100 degrees Celsius on the water gauge.

• Fans would kick on and mostly prevent temps from rising further.
• Coolant would be expelled from the puke tank out the overflow hose. I would regularly add coolant to minimize risk of overheating.

• But I didn’t like the rising temps so I decided to stop driving it.
• I also tried Patrick’s trick of blowing out the air bleeds. [Holley Carb Woes - DCDoug Pay Attention (Long Post) Hoping this would solve my problem, but same issues.
• Asking around, I took the car to a local shop claiming to specialize in the restoration of 60s muscle cars. [I say “claim” because the shop only had one person who worked with carbs, as I think the majority of their business was resto-mods etc]

• The shop could not replicate the rising engine temps, but admittedly I was not eager for them to take the car for long jaunts thru the Vermont countryside.
• The shop did however note the lag in the power band. The proposed solution was to swap out the carb from Shelby with a much smaller carb.
• Noting how well the engine ran when I first received it, I declined any modifications. Paid my bill for them not to fix the problem and took the car home in its original config.

Now:
• I have my original carb back from Dave Bergeron [thanks to Jeff for recommending!!] who rebuilt the carb over the winter. Dave said that the carb was mostly clean and he restored it to factory settings since I could not confirm if anyone had made any carb adjustments to where Billy set it.
• Since I already had the carb off, I opted to add a turkey pan. I have read about how the turkey pan changes air flow Turkey Pan on Side Oiler. Right now, I still have the basic air filter. Pretty sure it is the S&H that nobody seems to like other than for eye candy, so I understand that I might be swapping that out for something with increased air flow, like the K&N Extreme. If I can find one….
• I have always used ethanol-free fuel. Too many bad experiences with ethanol, so ethanol-free only. 91 octane is the highest ethanol-free fuel available here in VT.
• I just received my new Holley bits to re-plumb the fuel line to the carb to allow for the turkey pan. Carb and turkey pan installed. Everything fits well. No fuel leaks.
• Engine started and ran. Too rough at idle, requiring me to keep the throttle around 1100 RPM to avoid stalling. But I wasn’t too worried about that, as I have not yet followed Holley’s detailed instructions for setting the idle etc
• I paid close attention to the water temperature. Even at idle, water temp rose faster than it should. At least, faster than it did previously when it ran so well. Fans came on around 90 degrees or so. I cut the engine.
• After letting the engine cool. It re-started easily. After initial warm up, I gave it some gas. It backfired thru the carb and stalled. That was new, never previously happened. I don’t know if the shop last year messed around under the distributor. I certainly have not touched it since Billy first tuned everything.
• Per Dave Bergeron, I have fresh plugs to install once I think I have the carb tuned properly. Per Shelby, I have a new set of NGK R5672A-8 plugs. NGK recommends the gap for those at 0.0315”

So, what should happen next? Moving forward, I know enough about Troubleshooting to change one thing and one thing only at a time. Should I focus on timing before following Holley’s tuning instructions?
All insights welcomed and appreciated. Sorry for the long post, but hoping that this post will serve others in the future facing similar issues as I pledge to update this thread with my progress. Or lack thereof
~ Brian