1980 Blizzard 7500 plus. Starts kind of hard. Runs ok then loads up and boggs down. When it happens it wont rev freely and wont move the sled. Seems worse on an incline. Lift rear and let it wind up Seems to clear it out. Then will run ok for a bit. Almost seems to be getting too much gas and gets loaded up. I know compression it not great But when it does run right has plenty of power. Surely seems like fuel air mix or something simple. Also... Oil injection not using any oil. No clogs in tubes. Not sure how injection actually works. Are there check valves or something?