78E spark plugs crapping out - help?

[strom]

Hey guys...

A question regarding spark plugs on my old ex XS1100 standard....

After some riding, but within a few 100 miles the spark plugs die.
At the moment the new owner (a friend of mine) has burned through 4 sets of new ngk plugs and one set of old ones. Plugs just wont throw a spark, looks like they get overheated or something. If you replace them, the spark is good again - for a while.

The plugs color seems ok tho. Any ideas?
The bike is on stock air filter with home-made free-flowing exhaust headers and not so restricted mufflers. Stock jets in carbs, which are synced, alltho a bit more crappy than the usual stuff you get. Carb boots and vacuum membranes are new.

Ideas?

[Larrym]

Spark Plug Magic???

strom,

I'd want to see some tests done to confirm that the "old" plugs really aren't sparking. This would rule out other problems being the "cause" and the plugs being blamed.

Leave the "new" plugs installed in the head but take the old plugs and plug them into the spark plug wires. Then connect the cathode (the curved portion which connects to the plug side/threads...) to the engine with small alligator clips with wire between them. (NEVER count on them to make a solid electrical connection by just lying there on top of a metal surface...). Then crank the engine over in a dimly lit area. This would answer the question of whether it's REALLY the plugs or not.

If it really IS the plugs then I'd suggest measuring their resistance with a DMM. First measure the resistance from the anode (center of the plug surrounded by porcelain) to the metal piece that connects to the spark plug wire. (Use a "new" plug to compare the readings and get an acceptable value...). Then measure the resistance from the anode to the cathode. (You should get infinity to show that the anode isn't shorted out and allowing the spark to disappear before jumping the gap.)

I'm prepared to believe that the plugs are "dieing" a premature death. One possible cause may be the fuel or additives in the fuel in your section of the world. Maybe the spark is disappearing by running along a build-up of ??? on the porcelain.

Plug color ok?? I'd like to see a pic of the culprits to confirm that. May be able to see something you missed.

BTW: glad to know that your concern for XS's continues "Post-Sale."

[strom]

OK, I know the thread is a bit old, but still...

My ex 78E ran a bit, then died after 50-500 km, swapped the plugs (with another set), it ran again... repeat....

Since we didnt figure out anything useful (were too lazy), I just lent the friend who bought my 78E the 79 1.1 Standard until he sorts stuff out.

So, we figured it could be the carbs and one semi drunken evening decided to swap the carbs to eliminate rough running of his 78E and see whats up.

The 79 runs perfectly, plugs are perfect, jetting is spot-on,....
Well, what better bike to pull parts off of and diagnose the 78, right?

Anway, we swapped the carbs and his bike now runs a lot smoother, but on the test ride, it hesitated and cut out on one cylinder.

We decided to swap the plugs and it ran even worse after that - but only when under load. At a standstill the bike does not miss a beat. Under acceleration up and down the street, it would sputter and run like crap.

The carb membranes are OK - the 79 ran with the same carbs without issues 30 minutes before.

The pick-up wires are fine... we tugged and pulled and did all those horrible things to them and the bike didnt miss a beat (checked by ear and a stroboscope thingie).

So... its not the pick-up wires, its not the carbs, compression is OK, the fuel is getting to the carbs OK.

What else can we check?

Coils are lined up for a swap this afternoon... I have an extra set we will try.

What kind of problems can a ballast resistor give? I think there may be an extra one in my parts bin somewhere....

Well, we are open to suggestions....

[BigRed]

Your problem doesn't strike any chords loudly enough with me that I could say exactly what it is, but here's a list of suspects in the order I would check them. The good news is that this is all free until you get down to needing new ignition coils, and they shouldn't cost too much either.

1) Have you checked the voltage at the TCI and coils? You could be losing voltage in a dirty connector or bad ground... that would get worse as it heated up... then when it drops below 10.5V in the wrong place, you would get no spark. I had some bad ground connections at my voltage regulator.

2) Bypass the ballast resistor and take it for a real short spin (like to the end of your driveway and back) to eliminate that. It's bypassed by the starter circuit, so I think it should be safe to bypass for a very short time. Somebody else please chime in on this one if I'm wrong.

3) Look under the gas tank while the bike's running in the dark. Your ignition wires could be arcing against each other or the valve cover. Take the tank off and have a good look at the wires to see if the insulation is burned anywhere.

4) Swap the TCI with the one from your good bike, and you can eliminate that.

5) Unscrew your ignition caps and check the resistance across them. Most caps have a 5k ohm resistor, and it can fail.

6) When ignition coils are just starting go to, they can fail intermittently. It will get worse as they heat up. If you're going to replace them, I'd put in 3 ohm coils and get rid of the ballast resistor. One less old part to fail, and you'd have a little hotter spark.

7) Those first six steps cover your whole ignition system (you've already changed the plugs) except for the wiring between devices and your pick up coils. Your pick up coils could fail without having a broken wire. I've never heard of that happening, but anything can break.

Good luck!

[strom]

Just what I was thinking during the day today...

Anyway, I went to the friends place after work & lunch & coffee...

The bike ran fine after sitting on the centerstand overnight.

Took it for a spin and it ran fine.... weird. Gonna go for a bit longer ride tomorrow and in case of problems, go through the checklist you made.

Thanks!

[bikerphil]

Had a similar problem once, an intermittent cut off of the engine. Turned out to be corroded connector for the P/U coils behind the fuse panel and/or burnt P/U coil wire harness next to my 4-1 exhaust. I replaced the entire assembly with a spare and the problem went away for good. My bike would just stall at an idle sometimes but would start right back up. Might be something to check, good luck!

[strom]

Thanks for the ideas.

Also something we toyed around with (just as an idea)

Anyway, the friend came over, the bike running like crap again.

Added some more gas (was pretty low), and pressurized the gas tank just a bit with an air compressor.... that did the trick for now (happened once before and it also helped).

Did 120 miles with several stops in between and the bike ran fine so far.

Still, gonna check the connections and stuff...