Plugs fouling

[mike in idaho]

The spark plug center electrode should not go to ground, if it did the plug would not produce a spark in the gap between the electrodes. Spark plug caps come with resisters in them these days, they typically measure around 5000 ohms. A reasonable amount of resistance in the secondary circuit is a good thing, the coil (in good working order) will build up enough voltage to overcome that resistance and produce a hotter spark than it would with no resistance. Resister caps/plugs also suppress rf interferance(and are required on motor vehicles by the FCC), so you won't mess up your neighbor's tv/ car radio reception when you ride by on the street. Spark plugs can't be properly cleaned once fouled by gas or oil, abrasive blasting just removes the smooth surface of the insulator, making it easier to foul again. I never clean fouled plugs, it's a waste of time, they're seldom any good for use afterwards.

[jensey]

Hi,

The spark plug center electrode should not go to ground

You are right, measure from electrode to primary coil, my mistake,

Jensen

[Snakeoil]

Aero,

Feel free to leech away. You're not actually. It's a good discussion and if both of us are having similar symptoms then we probably have a better shot at getting to the root cause with two of us working it along with everyone else's help.

I'll see if I cannot run Jensen's tests this week and post the results here.

Best I can tell, my secondary side is all original short of the plugs.

Mike, I know what you are saying about cleaning plugs. My Dad inherited an AC commercial plug blaster from the local Buick dealership back in the late 60's when sandblasting plugs was determined to be no longer a preferred method.

But, when you are troubleshooting and can clean a set of plugs quickly to see if you get better spark, then it is still a useful technique if you don't have a spare set of fresh plugs available.

I'm sitting here wondering about the chemstry of plug fouling. Maybe a fouled plug that runs find in a hot engine will get worse when it cools down and moisture is present. It might turn a working plug into a non-working plug. This is just a side thought. Because I've changed plugs for brand new plugs and it still only ran on one cylinder until whatever is causing this cleared and stayed cleared.

regards,
Rob

[rrietman]

here's an old time mechanics trick for cleaning plugs. chuck it up in a vise and heat the tip with a slightly rich, oxy/acytelene torch. as the plug glows, you will see the carbon flying off.
Randy

[FluteTears]

I can remember my dad and my grand father doing that.
But most of us don't have a torch.
Wonder if todays Mepp gas torch would work hmmm.

[Snakeoil]

Okay, I'm back. I actually had to do a search to find my own thread. I did have a major life changing event in that I retired in Dec. Between that, repainting the inside of the house, the holidays, and being fully immersed in a '66 T120R restoration, I've only stopped by here to read the occasional email. The CL77 has been under a sheet since before winter.

With the Motogiro a month away, the Triumph was removed from the lift and the CL77 put in it's place. Today, I went thru all the components bit by bit. I did not do the secondary check that Jensen suggested, but only because I did not check this thread until now. I will make that check tomorrow.

I ran thru the coil primaries and both measured a nominal 4 ohms. Both condensers measure about .25 mf so they are within spec. Rotated the engine with my DMM connected to the condensor leads and the DMM set on continuity and could see the points open and close with no other leakage to ground.

Wiggled all the wires and connector during every check to look for issues and found none.

I do have a small resistance in the ign switch circuit, and will attack the switch with contact cleaner tomorrow after a trip to the store since I'm out of the stuff. But that should affect running in general and not one cylinder.

Measured the resistance in both plug caps (orignal) and got a nominal 7 ohms in 1 and 8 ohms in the other.

Checked the wiring harness for high resistance and got the same reading I got for the ignition switch resistance which was about 4 to 6 ohms. Wires were less than 1 ohm.

So, I had a new piece of copper core plug wire I picked up last year and with it I replaced the original plug wires. I cut into the original wire and looks to be aluminum. It is not copper. Did not check it with a magnet although I would not expect steel wire. What was the original wire on these bikes?

So, tomorrow, I do Jensen's secondary tests and if all is well, will put the battery in the bike and see how she runs.

If she continues to foul, I might move up in heat range to see if that helps.

regards,
Rob

[Snakeoil]

Spent a good chunk of the day studying the igntion circuit and how it is wired in the wiring harness. Made a few observations I'll share as well as had something happen to me that has never happened before.

First, checked general continuity between ignition terminal and positive battery terminal on ignition switch. Based on the readings which were in the 4-10 ohm range, but varied widely depending on how I wiggled the key, I decided it needed cleaning. A couple of shots with CRC contact cleaner, thru the drain hole in the metal switch body, cycled the switch a few dozen times, shot it again, cycled it again then blew it out with compressed are made two noticeable differences. First, the detents for the 3 switch positions were more pronounced than before with a nice solid click-click-click as I move the key thru the positions. And, a reading across the IG and BT terminals now gave a solid 0.4 ohms. So, if nothing else, the coil will see a little more power than they were before. Gave the lock cylinder a shot of moly lock lube when I was done.

The lead from the switch to the coils was good. The interconnecting wires between the coils, the condensers and the points were all good. Zero ohms throughout. I don't own a megger so I cannot charge the condensers to prove their functionality. But as mentioned previously, they are within the specs of 0.1 to 0.36 mF and mine both read a nominal 0.25 mF. As a sidenote, I went to NAPA to see about another issue and asked about condensers. Turns out a very common GM condenser with a separate clamping bracket measures 0.19 mF which will reduce arcing a bit. So, I have two on order as spares. They only had one in the store. Getting back to the condensers on the bike, I also measured their resistance to ground and it was infinite. So no leakage there. At least, not when cold.

Now for the coils. I measured the coil resistance between the negative primary terminal and the secondary terminal. Turns out the positive primary terminal and the secondary will give the same readings. I measured the primary resistance again to double check. Also measured the resistance of the entire secondary as Jensen had suggested. Then measured the individual pieces of that circuit to confirm the readings.

Here's what I got.

Right side
primary resistance 4.0 to 4.1 ohms
secondary coil resistance 7.92 Kohms
Plug cap resistance 7.95 Kohms (typo in previous message where I forgot the K)
Plug wire resistance - nil (this is brand new copper core wire)
Total secondary circuit resistance - 15.98 Kohms

Left side
Primary resistance - 4.0-4.1 ohms
Secondary coil resistance - 7.79 Kohms
Plug cap resistance - 7.75 Kohms
Plug wire resistance - nil
Total secondary circuit resistance - 15.69 Kohms

While getting ready to do the secondary circuit check, I pulled a new NGK D8HA plug out of my spares and stuck it in the plug cap. I got infinite resistance. I checked the plug an got infinite resistance. I ran the meter up to 20 Megaohms and got infinite resistance. This was the thing that has never happened to be before. I had a brand new plug that was flat out bad. Took it back to NAPA and kid behind the counter was very surprised. He's ordering 3 new ones for me.

I also ran thru a few more checks to prove out the functionality of the ignition circuit.

With my meter on the negative primary terminal of one coil, and the other lead grounded, I rotated the engine. With the points closed for that side I got zero ohms, with the points closed for the other side, I got 8.3 ohms, which is right because the circuit is now going thru both coils via the other set of points. I did this for the other side and got identical functionality and readings. With both sets of points open I got infinite resistance.

I then hooked my meter up on various terminals in the circuit and tugged and wiggled looking for something to flicker on the meter. Nothing. Every connection and wire was rock solid. So, I shot each connector with contact cleaner and reconnected all the wiring. Installed the wires back on to the igntion switch (I removed the feeds to the horn and tail lamp switch to avoid any back feeds) and installed the battery. Spun the motor over and had a nice hot blue spark on the right. Had a good spark on the left, but did not look as blue as the right side. But it was bright and consistent so I was content. I know the circuit is good so if the spark is weak it is either the plug or the coil.

Another sidenote regarding coil secondary resistance. I had no former experience making this check so no feel if 7.9 Kohms was good, bad, excellent or so-so. So, I had two other bikes handy with their coils readily accessible. My '66 T120R Triumph, with original Lucas 12 volt coils was about 6 Kohms. A 6 volt coil on my Aermachhi sprint, which looks very similar to the coils on the Honda were about 5.8 Kohms. So, I feel the Honda coils are in the ballpark for proper operation.

Buttoned the bike back up and she fired right up after her long winter nap. Both sides fired fine, although there seems to be a slight skip off idle on one side. But it was cold out (snowing at the time) and I was not interested in putting the seat back on and taking it for a spin. I can do that tomorrow when I run over the NAPA to pick up my plugs and condensers.

I also ordered a pair of D6HA plugs, which are one step hotter to see if that helps with the carbon fouling. The left jugs puffs a little blue smoke when I rev it so I might have to run a D6HA in that jug and a D8HA in the other. Might just run the D6 in both. We'll see how they look after a spirited run. I flog the bike pretty hard in the Motogiro so its akin to race conditions. The D6 might be too hot.

I'd love to hear comments regarding the readings I've recorded. I checked the book and no much info other than the condenser ratings. Based on all the checks, it should run fine. If she acts up again and I lose spark on the left again. I hope I'm in a position to tear into it right there and find the smoking gun.

regards,
Rob