Furnace problem

Well we camped this past weekend to close it up for the year and the furnace quit. It took a few cycles for it to start but after it started all was good till it cycled off. When the temp dropped and the thermostat called for heat; it failed to start. I do not believe it is the thermocouple as once it did fire it stayed on. I believe it is not getting proper ignition. After reading the manual, looks like the furnace needs to be removed from the cabinet and the electrode adjusted.

Has anyone gotten into this before and have any helpful hints?
I'm not in a rush because I've closed it up for the winter but Id like to fixit before spring when we'll be using it again.

Thank you
Jim