I have an 03 eiger that has been giving me problems for the last year. It is very hard to start when cold, after it does warm up it pops/backfires through the back of the carb. It does not have a constant idle as it revs up and down slowly. While riding it it does ok if while giving it constant throttle. When I turn it off after riding it, it seems to have built up pressure and backfires, or whatever you want to call it, it goes whoop!!! through the exhaust immediately when its turned off. I have throughly cleaned the carb twice and this did not help, new plug also. It has 750 miles on it. Not sure if this is a timing problem or valves need to be adjusted. Any advised would be appreciated.