Good initiative on your part to check head pipe temps.
Yes, do check your plugs. Note their condition and color of the center insulator. If any are wet you could still have an ignition problem. Check that the plugs are the correct heat range, too.
I don't understand peoples eagerness to dismantle carbs. I try to only do it when required. And, lots of performance issues get corrected with a standard tune up. (When you have a bunch of bikes, you ry to minimize maintenence time,)
Besides that, tuning carbs to an unadjusted, ill timed engine is just silly. But, if you liked the whack-a-mole game...
Having said all that, if everything besides the carbs check to book values, then check for fuel contamination. Even pristine carbs will give you grief if you feed them chunky fuel.
Clean fuel? Well if after these checks you still have cold pipes, then you probably do have plugged slow jets for those cylinders or the carbs are unsynced, badly.
Once you get the pipes even temped, and if the hesitation persists, then your 4 in to 1 probably requires a different carb set up. You can richen the idle mixture a bit with the idle screws. And/Or clip the slide needle in the next position so the needle will pull out of the jet more. You should then be observing more desireable color deposits on your plugs.
Good luck,
