I have found another problem with these engines. On the lock down ring for the throttle arm if it is not fully agains the butterfly then you will notice that the distance from the spray bar will always change. They have over machined out the butterfly so that there is way too much slop. If you think this may be your problem just open it at full throttle. Grasp the throttle arm and give it a slight pull away from the carbeurator and you will notice the distance changes. The way I fixed mine was to stick a wooden dowel down in the throat at full throttle and loosen the throttle adjuster plate and then slide it inward towards the carb. Then lock it down snugly. This is a pretty cheesy carb design if you ask me. But you get what you pay for. I am getting rid of my GMS engines and switching over to SK engines. Cheap, reliable and better design and built!!