I bought a digital tachometer and fitted it to the Square Four to get an idea of engine speeds as I run it in. However, it’s out by 4,000 RPM. The reason why, I believe, is that the tacho is for a single cylinder engine, and as it runs off the feed to the ignition coil on a four cylinder engine it reads too high - a fast tick over shows as nearly 4,000 RPM when obviously it’s more like 1,000.
Is there an easy way to fit a tacho to a square four? Maybe the easy way is just to renumber the dial!
Here’s a picture of the bike, the tacho is on the handlebar by the mirror. I plan to change the tank badges.
Square 4 mk1, Square 4 mk2, Colt, BSA C12.