I put in the new pm7 and it works ok for the most part until it sits for almost a day. When I start it up it has trouble and stumbles a little bit, then the rpms kick up to 2500 and after about 5 mins or so they slowly lower to 1000. The old pm6 I had it there started up fine and did not kick up so high in rpms and stayed right around 1200rpm. Any reason for this problem?