Jetting; seat of the pants or plug colour?

[dave wheeler]

Hi guys
since euro-lam last year ive been struggling with my series 1 li,if i jet by the seat of my pants the plug is slate grey, if i go on plug colour it 4-strokes like crazy, and there is never that biscuit brown colour, it goes from worrying grey to 4 stroking black in only 3 sizes (ie 107 -110). im running an sr175 barrel with standard carb and exhaust and using rock oil pp2 at 3%. Having melted and holed my share of pistons im anxious not to cause any damage but assuming the 107 setting is correct then why am i not getting a good plug colour?
cheers
dave

[Bofs]

You say standard carb but what size and what type?

[Darrell Taylor]

air cooled motors tend to show a grey tinge to the plug colour unless there cooling really well ,the greyness can be a sign that its a bit too high on compression/over advanced or even the plug grade is too hot ,id go with over advanced
id also try compensating for the leaner main by richening up lower down if possible (not sure on carb)

[dave wheeler]

thanks for the replies, its an ma19bs7, so it does have a needle to fiddle with, squish is 1.3mm, timed to 19 degrees btdc, could the oil have any bearing on the plug colour?

[Darrell Taylor]

try richening the needle a clip or 2 then and do you know what compression ratio the head and 1.3 squish equals ,if its high then id retard the timing back to 16 or 17 degrees