Sorry about resurrecting an old thread, but this discussion is very interesting to me.
My Beta 20 manual definitely says 30 seconds preheat but I ignore that. 15-20 in our cold winters, 5-10 in summer, 0 if recently run same day.
In a way I can understand an extended preheat 'could be' beneficial for some engines because glowplugs are captive in the head
and heat not just themselves but the surrounding areas of each combustion chamber. Just my theory.
My issue is that mine only starts on two pots and runs intermittently on the third for a minute or two before it smooths out to normal (governed) speed for whatever throttle setting. During this it blows a fair amount of white smoke which gradually disappears as the engine
settles to normal firing. Sometimes it fails to start first time but usually manages to.
This has to be glowplugs, yes? I checked them and they all glow. Cautionary tale - I checked one of them for too long thinking 'that's pretty' but discovered when it had cooled that it had deformed and wouldn't go back into the head!
So my question is... are glowplugs all or nothing or can they become reduced efficiency but still appear to glow when tested. And how do you measure their resistance?
Fox 31 "Vixen"