Now that I have my Kubota B7500, I seem to have a intermitant starting problem. Mostly on cold starts, nothing happens after warming the glow plug, pushing in the stop button and turning the key. I may have to go thru this for several minutes till it will fire and then turns right over. The battery seems well charged and I think the starter was changed a couple of years ago. I have just over 600 hours on the tractor. Any one have any ideas what might be wrong and how to fix?