A lot of times, it is as simple as a clogged fuel filter . . . simply replace it. If it does not fix the problem, it costs little and should be done regularly, anyway.
Secondly, it could be as simple as a need for a tune up . . . one that includes new plug wires and new plugs. Wires become brittle, especially in oily/heated environ and plugs should be replaced at intervals, anyway.
After this, take it to a parts house - have them put the scope on the computer. The reading/code it provides will tell the story fro you!