Plug Color Diagnosis

Hi all would like a little help confirming my thoughts please.
Background is.
71 Fastback full engine rebuild 600 miles on it. Just back from my first 'non running in' ride of about 200km. Bike running great.
Pulled plugs and found this.

Gapped checked hot plug it was only 2. It's now been reset.
My question is should I just lift the needle on the hot cylinder and then re check or see how it looks with just the re gap? I don't want to hole a piston so I guess I'm asking how bad does the plug look - should I react immediately or proceed changing one thing at a time.
Thanks in advance. Doug https://www.dropbox.com/sc/ssvan4enzcxn ... eaSnKp6vba

Saddlesaw said:

71 Fastback full engine rebuild 600 miles on it. Just back from my first 'non running in' ride.
Gapped checked hot plug it was only 2. It's now been reset.

Click to expand...

Are you saying that the plug gap was only .002"? What was it set at to begin with?
Was this with a proper plug chop, or just pulling the plugs after an easy loaf through the neighborhood on the way home?
What plugs are you running?
Have either of the header pipes began to color? If so, any difference in color?
Can you see any color difference between the two piston crowns through the spark plug holes?
How about ignition? Have you checked full advance timing for both sides?
Lots of things to consider...

Nathan

Hi sorry about the typo. The hot plug gap was .020. I have re set to match the other plug at 0.025.
It wasn't a "proper" chop but I didn't bimble home either and kept revs at 3000 plus until only a second or so before shutting off. Header colour is a nice even straw colour on both sides with no discernible difference between them. Plugs are Champion N7YX. Since rebuild I haven't done any timing work other than re fitting the tri-spark and setting the timing at 28 degrees.
cheers

too many variables to hazard a guess about the colors. If no operation issue then just switch plugs sides and see what happens until ya do real plug chop which may mean taking tools and camera with you. May find your ignition combustion system likes .020 better than .025. Get a V8 pack next time if plug reading to make sense of finer tuning.

As Hobot suggested swap the plugs over if the same cylinder runs lean this will rule out a plug issue. Check carb an manifold of air leaks that my be affecting that side (even if its single carb manifold it may not be sealed at one side). The old trick of spraying WD40 joint areas as engine runs an noting if it changes as a certain spot is sprayed works. If these don't show problem then carefully check both carbs (if you have two) it may be the lean side is ok but the other side has a problem an is running richer. Also if you have twin coils it may be them not firing correctly as with plugs swap parts from one side to another systematically will show up an issue. I would also do a compression check to rule out cylinder issue.

There are plenty of other things but they should give you a start. This is why many people favour a single cylinder motor

Hi,

assumed that jetting is ok and no air leaks, I would suppose an issue of the pilot air circuit.

Ralf