Posted by: Mike Clark
oooh - I see my post in another place has migrated here - no problem for me but perhaps Jeff you should put such tranfers in quotes.
I can bore for England on petrol in pilots so will just comment that I've never used anything other than unleaded petrol but have had a lot of work to actually devise a pilot that really works well. I have now got there but want to put a few more road miles on it before I tell you how I did it - one for the Steamcar at the end of this season. The secret is keeping the fuel hot til it gets to the jet and making the pilot strong enough to reliably light the main burner - to achieve this requires a better way of entraining air than just poking a jet in a hole.
A good pilot should be just short of being strong enough to maintain boiler pressure while standing. This means running at 850-900 on the pilot tell tale - if it won't do that it's too weak. Maxwell pilots are good at keeping the fuel hot because it is all inside the burner but the vaporiser is just too small to produce enough heat and there is no way of boosting it up.
Pilots without a needle through the jet do tend to block but generally with detritus in the fuel rather than the treacley stuff Peter mentions. Carboning up is a source of blockage if the pilot vaporiser is too hot.