I had some issues with my 2002 MXZ800 on a recent trip, where after it ran for about 20-30min. and we shut it down, it did not want to start easily(normally starts 1st pull), had to pull it 10-15times and throttle it to get it started. I thought it might be bad gas so I poured some dry gas into the tank, put new plugs in and it fired right up. So, I pulled it of the trailer, ran it for about 10-15 minutes, then shut it down and let it sit for about 5minutes. I gave it one pull and it started right up, so we continued riding it around at various speeds and shutting it off every so often and each time it woud fire right back up. After running it for about 20 minutes straight and somewhat slower speeds while I pulled my nephew on his sled, I jumped on the throttle a bit and it backfired. I ran it for another couple of minutes then shut it down and it would not start. I ended up holding the throttle wide open and puling about 10 times and it finally fired up, cleared out the cylinders and ran fine. Shut it down again and same problem.
In my haste to run it, I noticed that I did not close the carb deicing valve, so maybe this is still the problem as the outside temp was around 35 that day. Other than that, any other ideas? Could small cracks in the carb boots be causing any of this?

Thanks in advance

You might want to change your plugs sounds like one of them is fowling,you may want to check your boots also.My sled starts up that way to sometimes when its a warm tempuratue out.You may even have moisture in your gas which will make it backfire put some snowmobile safe gas line antifreeze in your tank next time you fill it up,good luck.

run br9ecs plugs too not the regular es plugs..