I have an older 5.5 HP billy goat leaf pickup machine. Since it is old, I put in a new carb, new spark plug and new air filter. The only way I can get it to start and run if I spray starting fluid in the intake. once it starts it runs just fine. However, as soon as I turn it off and try to start it it will not start - even when I stop and then try and start it again right away. What do I do now? the engine is getting fuel since it is running. What else should I change out?