Ok this may sound weird but here goes, I've been working on my Jag now for months. I run it every few days just to keep things loose.
Sometime when I start the engine it will have a ruff spot when reving the engine at around 1200 rpm. I'll let the engine come up to temp and run for 10 to 15 min. The ruff spot will remain even after warm.
Now for the strange thing, I'll go out 5 or 6 hours and start the engine again, no ruff spot. Nice and smooth through the rev range. Could it be something like a sticky lifter or something?
Would running Marvel Mystery Oil in the gas help out with this?