On the serial number, what does the "A" suffix mean. And, the manual downloaded does not that the UT10918A is included. The PDF notes UT105-40_60_80_339. Chainsaw will start and run for a minute or so, then refuses to rev up, then dies. Often very hard just to get an initial start. I suspect the fuel system needs cleaning. In have not digested the manual. Will it cover getting access to the fuel bowl, etc..?