i just recently bought a 68 t120 with a big bore kit in it .the problem im having is that when it is running its only running on one cylinder. so i tried adjusting the timing ,adjusted the valves,tried different coils.what do i do next.any info would help

What ignition system are you running ? Is it the original points set-up ? You have two of everything there so there are several potential sources. Do you still have twin carbs ?

If it has points check the condensers. You can isolate the cylinder by pulling off one of the plug wires. The side that results in the engine stalling is the good one, switch the condenser leads and repeat. If the stalling out follows the condenser then replace the bad one at least. I'd recommend you replace both but save the "good" one for a roadside emergency only.