R26 has a spark but won`t fire

[Steve]

Hello. I`ve finally managed to get a good spark at the spark plug on my R26 but it just won`t start. Any suggestions?

[Allan Atherton]

You don't say whether the bike was running OK until recently, or if it has not run in ten years.
I would check the timing and the valve adjustment and whether there is fuel in the carb.