Apologies for not posting earlier. Thought I had, but unsure so checked today.
The issue did not clear up with simply changing plugs although it did help for a short time. The problem became worse with intermittent backfire, cutting out etc. On the final occasion I avoided shutting it down, rocking the throttle out of frustration I guess, and it eventually threw a code which turned out to be "faulty engine head temperature sensor". Forty bucks and 5 minutes and it run better than had for some time. Googled this fault and came up with numerous others experiencing the same problems, most without codes. Turned out one gent with same issues was mapping his rpm and head temp when out of the blue the sensor temp peaked for a bit then returned to normal When it did it told the ECM to change the fuel mixture resulting in conditions we all were having. Apparently it did not throw a fault as the sensor believed it was still working condition or whatever. Thanks to those that responded initially, I hope that the delay with this final post did not cause others similar grief unnecessarily. Stepper.