Springbok Flyer

I have not run this engine for at least 2 years and it was badly gummed up. So I degummed all the push rods, valves and carburettor. After the clean up I connected the glow and it started up immediately. However, the top cylinder was not running, so I stopped the engine and checked the glow - it was working fine. I removed the tappet cover and checked that the rockers were moving properly - they were. I tried again and again, each time rechecking everything.

But alas, I cannot get the top cylinder to run - only 4 cylinders are running.

Any ideas and suggestions will be appreciated.

JanR