I’ve worked on dozens of those engines through the years, but even in Florida, where I live, I’ve noticed that you usually have to pull the choke out just for a second or two while starting them. After that, just let it off and everything is ok. I would suspect an air leak in the intake. The air cleaner system is designed to afford a certain amount of restriction to the system, so even without the air cleaner attached, they run way lean (at start up) and start hard until warmed up. I’d take some starter fluid and spray around any possible area where there could be an intake leak and see if the PRM comes up with the spray. If so, you have found your leak. It’s worth a try. Good luck, Ron.