burning rubber smell

[av8r]

So I was riding the other day and out of no where at a red light I started smelling burning rubber. After that the bike seems to be backfiring a little from the left exhaust. The bike is now a little sluggish at low speed, but ok at high speeds. I have checked and changed the oil and filter, checked the air and fuel filters. They are ok. So now when ever the bike is at idle after riding a little, it smells like burning rubber. I wonder if one or more of the valves is no longer in spec. I do not have the tools/expertness to check and correct the problem if that is the case. And I don't have $300 that the shop wants just to check the valve clearances. I guess the bike will sit for while... Maybe a bad oil pump?