Walk Behind Lawn Mowers

I purchased a new XT722FE lawn mower from Bomgaars on 6-19-2010. This mower has a keystart. Form day one I had trouble starting this mower. I talked to the manager of the Bomgaars store about this and he indicated a few things to check, such as too much oil in it. The amount of oil was what came with it from the dealer. When the mower did start it would smoke and backfire and run rough for a few minutes. Sometimes I would have to start it with the rope. Finally in late Sept he said he would send it in under warranty to get it fixed. When it came back they said they had to clean the automatic choke and there was a bill of $33.00. It still wouldn't start and this was observed by the store manager. He said he would send it back, which he did about three weeks ago. I checked with him yesterday and he said it still wasn't repaired and he had no idea what the problem was. I have no idea how the automatic choke could have gotten dirty in the length of time I had the mower, and that evidently was not the problem with the engine. Whatever the problem is it should be covered under the warranty. Please advise why it is taking so long and why there is so much problem with this mower. Darrel E. Smith