2009 Husky Te510 Backfiring (4 Stroke)

I appreciate any help to my issue. Recently took my bike into a local dealership for this problem. After 3 weeks all they can tell me that they don't know what is wrong with it. They changed fuel and set the spark plug gap (which I already did and with a new plug). They want $165 for this. Sorry for the long thread but the more info, the better.

Issues:
· Engine will not start, only backfires. I changed the spark plug with a new one. I noticed that the HT wire from the coil will pull out of the spark plug boot. Not sure if this is normal or not. Could be the problem but didn't seem to affect it before.
Story of this bike:
I bought this bike about 2 mos. ago from an individual in Solvang,, Ca. I wanted a dependable trail bike but did not want to buy new. I rode it and it ran good, shifted through all gears. The person assured me it was well maintained by his local mechanic. It had full oil in the crankcase and coolant in the radiator. The only thing I noticed was the brake light wasn’t working. I figured a burned out bulb or switch was bad. I didn’t think this was a big deal so I purchased it. Little did I know the brake light was trying to tell me something.
Previous owner had some aux lights installed on the front fender, they were connected to the headlight wires. He removed them and clipped the wires. I removed all the splices, cleaned up the wiring and put back together to original condition. I also installed new LED turning signals. Lights all worked fine except for the rear brake light.
I hooked up a test light to the brake contacts on the rear brake light socket, actuated the rear brake, then the front brake, nothing. Checked the bulb, it was good. Put in a new bulb anyway. Check fuses, all good. Cleaned the fuse contacts, nothing. Disconnected rear brake switch, did continuity check, it was good. Checked front brake hand brake switch, found bad. Replaced front brake switch. Hooked it all back up, brake light still not working.
At some point in time, when turning on the ignition, the lights would not come on except for the headlight low beam. Horn, taillight, headlight (high beam), turn signals would not work. Battery was ok. I tried to find a wiring diagram online but could not find one clear enough to read. I experimented with jumping some wires and found that if I jumped 2 wires at one of the relays on the right side under the gas tank, all lights would operate normally including the brake light. These 2 wires are currently soldered together. I was going to replace the relay but at $185 I figured I’d try a work around. At the same time, I was interested if the fan would turn on from the temp switch. I removed the connector from the switch on the cylinder, jumped it and fan would not come on. I traced this to the relay on the left side under the tank, jumped 2 wires and the fan would now come on. I wired this to the black switch on the LH handlebar so I can turn it on manually. I did not cut the wires, only jumped them. I have no idea if the fan will automatically come on if the temp switch is tripped.
During all this, the engine would still start and run normally.
I did some more work on the bike. Cleaned the chain and sprockets, removed the old radiators and replaced with higher capacity tanks, changed the coolant with new, removed and replaced the coolant hoses. While working with the radiator and coolant I also changed the coolant in the overflow tank. I had removed the tank from the bike and found the plastic nipple was a solid piece of plastic not allowing coolant from the radiator to go into the tank. I drilled out the nipple and the tank now accepts coolant from the radiator. I also replaced the air induction boot and air filter with new ones. The old boot had a ripped nipple from the air induction boot where the engine oil breather was attached to it. I removed the 2 aft exhaust pipes and wrapped them with insulating wrap. I did not remove the header pipes.
I changed the oil and main oil filter. I did not have o-rings for the other 2 mesh filters on the LH side of the engine so I did not clean them.
After all of this I started the engine and it ran fine. Bike was in garage for about a week. I started it up, it ran for a bit then started backfiring and quit.
Help!

Hello, not sure which forum to direct you to, but surely there is one devoted to your model, (mine is about 34 years younger than yours :<)) but there has to be one on here somewhere, it 's a great site! Best of luck with your issue! Perhaps a call to John at this site can either guide you or recommend a source:<) He has helped me a bunch!

http://www.vintagehusky.com/

Regards,Steve