i have a 240 vitos big bore with a 35 pwk carb. at 3/4 to full throttle after 3rd gear i get this noise in my top end that sounds like preignition but slightly diff. when the noise gets really bad engine will stall. it will refire and noise will be gone until i do as described above. i also notice alot of unbunt gas/oil on my a-arms and exhaust flange. when its in neutral i can rev it completely out with no noise. only starts after 3rd grear and only when 3/4 to full throttle. i'm getting very frustrated and have tried many diff combos of main jets and needles. if anyone has experienced this please give me some ideas of what it might be.