I would pull a spark plug wire a 1/4 inch away from a plug and watch the spark when it starts acting up. If spark stays steady and strong, check for fuel issue. If not, troubleshoot on the spark side. First step is always isolating issue to either spark or fuel. Resist the advise to start throwing parts at it. I can hear it already... "change the condenser", "Change the coil", "Check the blinker fluid", etc. "My car did the exact same thing, and it was the wrong weight oil in the rear end"!
