The weather yesterday was slightly above freezing and a lot of the snow had gone so I thought I would give the engine a try. It started ok but wouldn't rev and was very 'touchy'
I tried to think back over anything else that could have changed. Finally I remembered that when I installed the electrical system I had mistakenly installed a 7812 regulator for the ignition instead of a 7806. I spotted this when I checked the voltage on the coil and found it was ~7.5V. The engine ran ok like this for some fuel injection trials but when I had a free moment I installed the correct 7806 but didn't check anything.
The voltage on the coil when the engine was running was around 2.5V
I connected a 6V accumulator directly to the coil and tried again, everything back to normal
I made few more checks back in the workshop. With the points open 6v on the coil points closed 2.3V on the coil, current limited to 1A. I connected the 6V accumulator again and measured a current of 2.5A points closed and 0.6A with the engine turning at at least 1500rpm. This is the current I had used to decide that a 1A regulator would be ok, but the inrush spikes were obviously activating the current limit. I then connected a 2200 microfarad 25V electrolytic capacitor across the output of the regulator and tried again. The voltage drooped with the points closed but maintained 6V when the engine was turning.
Although the snow has returned I decided to give the engine another try this morning. I spite of sub zero temps it started instantly and will rev to around 4000rpm as before (quite enough for a cast iron spoked flywheel
). The carb I was using doesn't really match the engine so I have to adjust the needle valve for different speed ranges.
There was also no sign of water leakage from the water pump shaft
This time I have just pasted the link in rather than using the YouTube button above