Dale stevens, :welcome: aboard to iboats...
Sounds like you are getting a heating issue with the spark. One thing you can do to point to the problem is while running, once the problem seems to be going on. remove the spark plug boot from one cylinder and see it the engine's RPMs change. If so that cylinder is working. If not then you found the cylinder that is not firing and you can start testing the coil and such. One good way to see it the coil is a problem after locating a suspect one is to swap the coil with a known good one and try those tests again. It the problem follows the coil, bingo, you found you bad part and time to replace it. If the same cylinder still has problems, then the ignition system that goes to that cylinder needs checked. JMHO!
