I just bought a 1978 Garelli Super Sport. The bike wasn't used the last two years. After a few days of trying to get it started, it finally turned over. It was running fine, then it wasn't. I cleaned the jet out, emptied the fuel tank and cleaned the screen in the fuel tank. I also had the throttle cable replaced. It was running fine, the it started to bog. It felt like it was vapor locking. After a mile of this it stopped and ran great. Then the problem started again. If I let off on the gas for a few yards, it wouldn't die and it would then pick up speed. Now I can't even get it started. Any suggestions?