I think that you should be finding yourself another dealer, even better, an independent. They are quite obviously not bothered with resolving your problem. How difficult would it be to get the mechanic to take a quick run up and down the road with your bike to feel the problem himself? If it's that serious and they tell you to keep riding it to 'let the chain bed in' (what bullsh*t!) then they aren't worried about your safety either. If I thought a chain was that bad I wouldn't be suggesting someone rides the bike any further, if it snaps it can do some serious damage and not just to the bike. That's not even to mention the fact that they are the ones that adjusted it (if I understood you properly?) and didn't bother checking that it runs properly. Unless you neglected the chain badly I doubt it would be worn out enough after 7500 miles to cause something like this. The fact that it's at a specific rev range suggests something else.
You can't check or change the rear spark plug without lifting the tank. If they claim they didn't lift the tank, they also couldn't check the air filter. If they charged you for changing spark plugs (and the air filter) it's fraud if they say they didn't lift the tank, either that or they are lying about not lifting the tank. I always tell my wife to tell the garage that services her car to put the stuff they replaced in the boot, that way I know they actually did it, but even then I find things they didn't do that they should've.
It sounds like there is a lot of honest money to be made as a bike mechanic at the rate that these dealerships are forcing customers out the door
It's poorly after they 'serviced' it, I don't have any suggestions, but I sure wonder what they did to it...
