Look at the easy stuff first. Though valve clearances and timing are very important, they aren't likely to cause the behavior you are describing.
The most common problem on the early carbs is fuel starvation (in my experience). Turn off the fuel at the petcock and confirm there there is fuel in each carb bowl. If not, then you need to redo the carbs. Consider adding small inline fuel filters if you don't already have them. Check your float heights and clean out any clogged jets.
If there is adequate fuel in each carb bowl, then it is time to check your spark plugs. Pull each one out (one at a time of course), keep it connected to the coil cable, ground it by touching the end of the spark plug on the engine fins, turn the kill switch to "on" and press the starter button. You should see strong spark in all four sparks. Again, do this one at a time. If one of these fails, you can trace it back to make sure the coil is working and if the points are working.
If those two tests come out ok, then the most likely problem is a short somewhere. Take the tank off, set up an auxiliary tank, set up a fan to cool the engine and run the bike on the center stand. Start playing with all of the cables to see if you can get the bike to run poorly. I've found bad grounds, lose cables and eroded connectors like this.
Good luck!
