Bonneville America Forums Forums Technical Forums Performance Mods How do you read this sparkplug

How do you read a sparkplug that is white and dark brown?
I need some thoughts from the masses here.
Here is some pics.

Mine do the same thing. Dark on one side, white on the other. I'd say too rich. Speculating, only way I can see it could happen like that would be the flow in the combustion chamber.

Are your plugs side-cut? I was thinking maybe I cut too much off and it is firing more on the one side.

Does anyone remember back in the 60's the home made 'spark boosters' that some kids installed in the HT leads ? They split the HT lead and introduced another gap that the spark had to jump before the plug.

How long have you had those plugs in the engine? The center electrode looks worn on one side. Did you try to side gap the plugs? Looking at the gap it looks too wide. The spark appears to be flowing sideways bacause on the uneven electrode wear. Appears to be too rich but how did the engine run before you pulled the plugs?

The "spot" is where the plug is indexed in the cylinder (meaning that spot is aimed at the exhaust valve). There is a lot of debate if there is any merit taking the trouble to index plugs. The "ideal" place is 180deg opposite the electrode base.

Looks to me like you side gapped the plugs .

Gap looks way too wide to me.

Here is the history. My plugs have always been mostly white, that’s my cat’s name (mostly white).I’ve tried regular, iridium, and side-cut plugs. I settled on the side-cut plugs because they seem to give me better response. I’ve up the jets to 135’s, 45’s, put in TBS needles with one shim, and the wrench at my Triumph shop snipped the needle springs. The exhaust was Thunderbike then changed to the short turnout Harley pipes. The air box was drilled out on the bottom with a K&N filter.
With this setup it runs good but the plugs only had a little bit of light brown where the dark brown is now, also at full throttle it would lose acceleration at about 90 mph but if I eased off the throttle then eased it back up it would accelerate again to 110 mph, probably more but that’s all I have room for around here til ya go into the curves.
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In January I put in the Freak with the 160 mains that comes with it. I didn’t change anything else cause I was trying to richin it up a little. It did get richer but still only on one side. The acceleration deal is still the same. I’ve only had one day to ride this year so everything here is based on that one days ride, about 150 miles of mostly speed limit riding. She seems to run good though.
Oh, these were new plugs before the Nor-East Rally, about 3000 miles on them. The light spot on the post is not wear it is a light gray spot.
I was wondering if I side-cut them correctly, maybe I cut them to short but I get the same pattern with the other plugs I tried.
I hope this gives ya a bigger picture of what my setup is.
Thanks for all remarks!

I look at the picture and I read,"NGK". That help ya?




Lemme know if I can help anymore.

Pat, I was waiting for you to jump in here and I knew someone would make that remark. I just thought it would be Matt or Mark
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Gregger, I think a new plug left stock sounds like a good idea. I can't test it for a while til we get rid of this winter weather though.

Well thats a tough one to read, I agree. My first impression is it may be slightly lean due to the white side but with 160 mains and 45 pilots with a snipped spring you would more likely be rich. I don't know if side gapping causes the dual color or not since I don't side gap mine and never have.

Snipping the spring will allow the slides to open slightly sooner and faster giving better throttle response if done correctly.