Yup, agree also- try to increase it by .004″ at a shot- this may require making up a shim that is thinner than the one in it- Or, you could take .004″ off the sealing surface to drop it further down into the liner. Do this until it runs consistantly or else there is a drop in rpm. If the needle gets touchy, that means it is over compressed- and, finally, if you are blowing plugs, you have gone too far too-
The other thing that may help, if the engine is cowled, is to block off any cooling holes in the cowl. If uncowled, then a “clamp” can be made out of aluminum that surrounds the cooling fins. This acts as a heat sink and may keep heat in the cylinder- used to do this with Rossis in the olden days….