I don't think you should use 0.9 inches as a plug gap ....(maybe 0.9mm image). However, I don't think the absolute size of the gap is a big issue. I have run about 25 to 40 thou for years on all manner of cars and bikes, and even closed a four stroke bike down to about 15 thou when the battery was flat and the spark was weak - and that fired it up a treat. Small gaps are prone to fouling, big gaps are too far for a weak spark to jump, but there is a world in between of big fat sparks and healthy running.

If you want to worry about performance have you checked the timing of your camshaft ? I finally got round to doing that on my 'other' V8 and found it was 6 degrees out. Now that does make a little difference (but not a huge one - the V8 is hardly an F1 engine) !

I wouldn't worry about spark gaps very much, though they tend to open up with age, so set them down to the lower end of the range (25-ish thou), and then forget them for a long time.

Steve


There's a lot of talk these days about green transport. Well, I am ahead of the game, I already have green transport ... British racing green.