Bought aircraft in January and follow start engine checklist to the T. As the ambient air temps have been scorching in Montana this summer, I find the engine needing three to four times as long engaging the starter to get it going, sometimes have to stop cranking and wait a few minutes before engaging again. I have not changed the sequence on my start checklist one bit. Is this strictly due to high outside air temps? If so, what do you pilots in AZ do in the summer to get better or easier starts? If not, any suggestions? KMSO elevation 3200 feet, density altitudes routinely between 5000-6000 feet this summer. One day with humidity it was 8900 feet!!