Thor 100 PWK Mixture/Temp.

[Steve]

It took the best part of a year but repeatedly trying to tune my Thor 100 was seeming impossible. Eventually, to get a good plug colour (fresh plug chopped, one from WOT and another at 1/3 throttle) meant having an engine that ran badly in the lower revs, there seemed to be no logic.

In desperation I raised the needle clip one position as common sense said the problem was it being too rich in the first 1/3 throttle. Suddenly the engine transformed and at last seemed to be running properly. The problem is that the plug disagrees and is grey to light grey. Not white and no deposits but it is saying the mixture is a bit lean.

My CHT gauge refuses to show the engine under any excessive heat, I can cruise for twenty minutes and it doesn't go above 160-170 degrees C. On a full throttle climb it never exceeds 204 degrees C. From memory I think Polini say not to exceed 240 degrees for the Thor 100 but I can't find that reference.

The bottom line is that the engine runs nicely, the CHT gauge says all is well but the plug is grey. Any expert opinions gratefully received.

ps - After a few minutes cruise, any attempt to go to more throttle for a climb just bogs down. It can take a few seconds or sometimes quite a few seconds to clear after which she runs lovely again. This engine has always done this and I eventually put it down to carb icing although I am aware of a build up in the crankcase can also give this symptom. I ran Silkolene FST for a few months and this did seem to improve things although it never went away.