1) Replace the battery.
2) Increase the dwell. Try using the stock setting (52 blinks with stock board, 34 milliseconds with aftermarket board), or if you have a QEV you can try it at 16 or more blinks (16 or more milliseconds with aftermarket board).
Guide to finetuning Dwell:
3) Clean and regrease the regulator. This is most often the cause.
Regulator maintenance guide:
4) Clean and regrease the firing assembly and solenoid. Be sure not to overgrease or undergrease the o-rings, as either can cause the problem.
Firing assembly maintenance guide:
5) Make sure your tank is screwed in as far as possible.