I have a 2005 cat 500, our problem is after running for about half an hour it starts backfiring and missing real bad, then after it cools down for awhile it takes off again for about another half hour. Any Ideas??? Or can anyone recommend a mechanic in the Portland Vancouver area? Thanks for any help.

 

The backfireing is a sign of lean. Ill bet the float bowl is running dry. One of the vents is probably plugged, with mud or dirt. There are one or two vent lines on the carb, and one on the gas tank. The next time it starts to backfire...remove the gas cap right away, and if that gets gas flowing again...the tank vent is plugged. If that doesnt help.....then the carb vents are probably plugged. The vents are connected to the little rubber hoses, theres at least one on the bottom of the float bowl. Pull the rubber hose off, and try to blow thru it.

 

Had about the same problem with another brand. I found weak coil,cdi. When ignition system got hot it would break down and cause sputer and die. When mine did that I hooked up a spark tester and found weak and erratic spark. Hondabuster's ideas are spot-on also.

 

check your valves make sure they are were they should be adjusted