My spark plug is... Yellow?!

churlburt

churlburt

Active Member
Hey everyone,

Just got my 1972 CL350 up and running after spending all winter restoring it, now I'm just working on the fine tuning.

It starts up and runs great, however I have noticed a popping sound on deceleration at times from the left side and sometimes while holding a steady speed like 40MPH it is not completely smooth, it seems to lurch or sounds as if its missing for a split second. It is a very subtle feeling/sound.

I suspected a slightly lean cylinder and pulled the plugs. I noticed the right plug was quite dark while the left side, the side with the popping on deceleration, was a grayish brown color and looked slightly lean to me...not overly lean so as to cause great concern. Anyway, I decided to get new plugs (the ones I was looking at had been used quite a bit) to get a more accurate reading.

Long story short, got new plugs rode about 50 miles and pulled them out tonight to find that the left one (the side that previously looked lean) was YELLOW. I have never seen a yellow plug before in my life and have no clue as to what it might indicate. The right side appeared to be rich. I've attached pictures so you can see exactly what I mean.

Running NGK BR8ES plugs
100LL Fuel (Which i suspect might be a contributing factor to these issues some how...)

If anyone could shed light on this, it would be greatly appreciated. Also, i'm kind of a carburetor newbie so what would you guys suggest as the best way to adjust the mixture to make it more lean or rich accordingly? Does the mixture screw affect the fuel/air mixture across the entire throttle range or will I need to swap out main jets to attain the correct mix?

thanks!

Left side:
IMG_0989_zps9d48bd65.jpg


Right side:
IMG_0990_zps804c4478.jpg
 
Does anyone have any ideas whatsoever? does the yellow plug appear to be excessively lean to the point where I should not ride the bike?
 
It's lean. Sync your carbs. Why are you running leaded gas?
 
Rich Ard said:
It's lean. Sync your carbs. Why are you running leaded gas?
Click to expand...

Did you google that or did you just happen to know that lead fouling causes yellow plugs?
(I googled it, I'm too young to have used leaded gas in anything but airplanes)
 
I knew about the lead fouling - but i had to look up the fuel.
 
I just figured somebody had peed in his gas tank....


See, there's that one in three Rich is always talking about
 
This reminds me of back in the day....

We had massive parties at my friends house, and every time after a party the next day Mike would find his laundry basket pissed in. Every time.
This went on for a few months with a party every weekend or so, until finally he woke up mid blackout pissing all over the clothes in his laundry basket and laughing hysterically.

I suppose the moral of the story is lock your gas tank if you're going to be drinking heavily, and move your laundry basket away from the bathroom.
 
Re: Re: My spark plug is... Yellow?!

SONICJK said:
This reminds me of back in the day....

We had massive parties at my friends house, and every time after a party the next day Mike would find his laundry basket pissed in. Every time.
This went on for a few months with a party every weekend or so, until finally he woke up mid blackout pissing all over the clothes in his laundry basket and laughing hysterically.

I suppose the moral of the story is lock your gas tank if you're going to be drinking heavily, and move your laundry basket away from the bathroom.
Click to expand...

One time when i had eaten a bunch of mushrooms I puked the beef stroganoff i'd eaten earlier into a trashcan next to a store. Which turned out to be a laundromat. And it wasn't a trashcan.
 
Rich Ard said:
It's lean. Sync your carbs. Why are you running leaded gas?
Click to expand...

I had access to 100LL and figured I would try it. I have no good reason...just what I happened to have in my gas can at the time. Is leaded fuel particularly bad for the engine?
 
Without high compression pistons it wont run well with 100 octane. Stick with 87-89 like the bike is built for
As far as the lead it shouldn't hurt as these bikes were built when gas was leaded.
 
You are correct that it's two factors. First is that 100LL has lead and TEL and other additives do color the plug. The other issue is that Unleaded leaves a lot of carbon on the plug because of the chemical composition and carbon-carbon bonds.

Empty the tank and refill with street unleaded and do a plug chop at WOT under load. Part throttle chops are very misleading and cause people to jet wrongly.

Then look at why the right side is burning oil or is that carb really so rich? Check jets are airways and carb synch and float levels to be sure.
 
thanks a lot, you guys have all been very helpful. I've synced the carbs so the idle stops are in the same place and they pull at the same time with the throttle cable. Unfortunately, there is no place on the 350 to hook up a vacuum gauge so I got the carbs as closed to synced as I could.

next step I'll drain the tank and get regular fuel in there.

im going to go through first and make sure everything is correct with the timing and valve adjustment before I make any changes to jetting as it may not be necessary.
 
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