Riding Lawn Mowers

We have a Husqvarna YTH2148 lawn tractor with approx 800 hrs. Over the past couple of weeks, the mower blades will sometime engage when you pull out the PTO switch and run okay for a while then just stops running. I can turn it off and then restart the mower, pull out the switch and sometimes it will start again. But it has been getting worse and sometimes won't stay running any longer than 3-4 minutes. As of right now,it will not even come on. When we pull the switch, we can see the meter volt move, so we think the switch is fine. We talked to a service tech at Husqvarna and they mentioned something about an "air gap" (which I assume is a gap between the magnets)and to get with a service center and have them reset the gap. I have talked to some dealers and they can't get to it for two weeks or longer. Our grass is growing fast and we have a son that is an auto mechanic, so I think we could do it if we knew the gap sequence or setting. Do you have a book or anything that will tell us how to do this so we can get it fixed ourselves.