One thing you're doing wrong is running too much oil, cut it back to 16% and run a Fox Miracle plug, a Saito SS plug or an OS-f. Cut the nitro back to 10% max, early on when yours was mfgd the recommended fuel was WildCat 10% fuel with 16% 80/20 syn castor blend. Even 18% lube will make the engine run wet and smoky in the midrange.