When you take the cover off, you will see the flywheel and below that is the carb. In between both of these is the timer base. It's a black plastic strip that has a shaft with a plastic bearing that rides on it when you throttle up in gear. The throttle moves the timer base, which moves this bearing and shaft that is hooked up to the throttle. It'll open the throttle relative to the spark advance so you don't bog the engine with too little spark advance. When you go to Wide Open Throttle ( WOT ), that part that rides on the timer base will pull away from the timer base as it is being pushed by another wire since the timing has been advanced far enough that the throttle can be controlled seperate of the timer base. Check the operation of that when it is cold and see if it is operating properly. If you don't know for sure, go out to the lake and watch how it operates when it acts up, and how it operates when it doesn't. If it acts the same way for both scenarios, then it's not an issue with the timer base sticking, etc. ( I have the same motor with tiller )
