hot cylinder after rebuild of twin cam motor

[Rich]

I recently rebuilt my twin cam motor and now number 4 cylinder is 200 degree hotter than the other 3 which measure 300 degrees at the exhaust manifold after running the motor in an engine stand for 5 to 10 minutes. I have an after market 4 into 2 into 1 ceramic metalic coated headers so its easy to read each exhaust tempature. I switched the front carb with the rear and number 4 is still hotter than the others. I can't find any air leaks in the intake and all the jetting across the carbs is the same. The timing is right on and the leak down and compression in number 4 is the second best of all the cylinders. Any suggestion as to a solution will be appreciated.
Thanks

[nmauduit]

is it a Stromberg head ? if so at what rpm did you have the engine run before measuring the header temperature ? I suspect that at idle the flow could be easier to imbalance (inlet differences, ) than at say 3000 or 3500...

[Grizzly]

How well does the vacuum balance up across the carbs? I had issues with my rear carb too that turned out to be a mixture of the Inlet manifold flange being slightly warped, new o-rings being too hard and a leaky servo (+2). One of my symptoms was much higher temps on the no four branch of the exhaust manifold on progression also a very lean colour to the plug.

I think i may also have had a bad valve guide too as they were replaced at the same time (it was a bit smoky on cold start up) but just like you i did a compression test, Leakage test etc and all appeared well.

[Donels]

Maybe there is some blockage in that exhaust pipe causing a higher back pressure?

[mbell]

Have you checked valve clearances since fastening the head down?

[Chrispy]

Hows your valve clearances?