nytrdr24
+1y
w/o the full exhaust on it, your tuning efforts will only get you in the ballpark.....but i'm sure you know that. the header is equal length tubing, so that shouldn't be a factor in the #4 cyl being hotter than the rest.....now that you've changed the timing, what was the temps on the runners of the individual cyls? about the same as each other or different?
do double check the plug wires, make sure to use some di-electric grease on the connections at both the plug & distributor....also the plug gapping can make a difference, make sure they are all set @ factory specs unless you have a cam or something else that would justify running a different gap...double check that all the plugs are the same, the parts counter peeps have been known to slip up every now & then and mistakenly give you one plug hotter than the others.....
best solution on the vac caps is to go to an electrical supply house & get some heat shrink caps & shrink them on the ports, use the ones with adhesive in them, once shrunk onto the ports, they won't come back off!
if the plugs are copastetic, and no vaccum leaks, and you get the exhaust on fully & timing right & your still seeing issues on the #4 cyl, it could be like bj said a weak exhaust valve spring, no adjustment on the hydraulic lifters although it could be sticking....the only way of checkin a spring is to use a spring compression tool & measure it against a good spring to see if their rate is constant through the motion...nothing short of a pain in the arse considering you'll have to pull the head, & if going that far, it would be faster to just replace all of them & put it back together than to see if just that one spring was bad...
hope you get it fixed w/o too much agrivation!