K75 Spark Plug Wires

I've been trying to diagnose some trouble on my K75 (difficulty starting, often leading to engine flooding, then a rough idle). I wanted check that the bike was getting good spark.

The only test I can find in the aftermarket manuals is removing the plug, grounding it on the cylinder head, cranking the engine and examining the spark. There is a spark when I do this, but not a "fat blue spark" as described in the manual. More of a white spark. The plugs are new.

My next idea was to check the wires. I looked down into the spark plug end of the wire, and it seems spotted with green corrosion. The metal lead and a k-tech IBMWR article by Mr. Eilenberger suggest that the resistance end to end should be 5k Ohms.

Since I don't have a multimeter and I live near Bob's, I took the wires in and asked them to check the resistance. A tech came out and told me they wires were "dead", no current going through. Then another tech came out and said that the wires are untestable, something about the nature of the leads ensuring a dead reading every time. Does anyone know whether this is true? It seems like it makes diagnostic work a bit of a challenge.

Went to the counter to price new plug wires, and noticed that the part numbers have changed. My wires are numbered 12 12 1 459 585 (586, 587 respectively). These wires are NLA and the new numbers are 12 12 1 459 874 (875, 876). Nobody at Bob's knew when the change occured or whether the new wires were different in any significant way. I did notice that the K75 wires are more expensive than the wires for any other K model, dunno whether this has always been the case or has something to do with the new wires being some upgraded version. Anyone know about the new versus old plug wires?

Jeremy Smith
Chevy Chase MD

K75T said:

I've been trying to diagnose some trouble on my K75 (difficulty starting, often leading to engine flooding, then a rough idle). I wanted check that the bike was getting good spark.

The only test I can find in the aftermarket manuals is removing the plug, grounding it on the cylinder head, cranking the engine and examining the spark. There is a spark when I do this, but not a "fat blue spark" as described in the manual. More of a white spark. The plugs are new.

My next idea was to check the wires. I looked down into the spark plug end of the wire, and it seems spotted with green corrosion. The metal lead and a k-tech IBMWR article by Mr. Eilenberger suggest that the resistance end to end should be 5k Ohms.

Click to expand...

Ah jeeze Jeremy - Mr. Eilenberger is my father, and he's 86 years old.. I'm just Don..

As far as testing resistance of K bike wires - the number 5K Ohms is specific to the 4 cylinder models (and it appears the later K11's may be 6k - still tracking this info down)

The K75 uses a plug wire with a gap in it - which is another way to shorten the spark time length and lessen RF interference. Dunno why they didn't use a resistive element like they did on the 4 cylinder engines - but they didn't.

Since I don't have a multimeter and I live near Bob's, I took the wires in and asked them to check the resistance. A tech came out and told me they wires were "dead", no current going through. Then another tech came out and said that the wires are untestable, something about the nature of the leads ensuring a dead reading every time. Does anyone know whether this is true? It seems like it makes diagnostic work a bit of a challenge.

Click to expand...

The second tech was correct - the first one doesn't know of what he speaks. You will read infinate Ohms on any K75 wire - which a mechanic would interpret as a dead wire.

Went to the counter to price new plug wires, and noticed that the part numbers have changed. My wires are numbered 12 12 1 459 585 (586, 587 respectively). These wires are NLA and the new numbers are 12 12 1 459 874 (875, 876). Nobody at Bob's knew when the change occured or whether the new wires were different in any significant way. I did notice that the K75 wires are more expensive than the wires for any other K model, dunno whether this has always been the case or has something to do with the new wires being some upgraded version. Anyone know about the new versus old plug wires?

Jeremy Smith
Chevy Chase MD

Click to expand...

I haven't heard of a change in PN's - but sometimes these are just a minor change or even a numbering change in the PN scheme.

While it's possible that your wires have failed - it's not very likely that all of them have failed at the same time. IF the spark you see on the plugs is the same for each cylinder - in all likelyhood your wires are fine.

I have not heard of a great number of K bike ignition wire failures - my '85K100RT still had the original ones in it when I sold it, and my current '87 K75S also has the original ones in it. I would expect them to easily last 100k miles or more, especially with the K75 wires since the most common failure of wires is an increase in resistance caused by the resistive element failing. The K75 wires don't have that point of failure since there is no resistive element.

I'd be looking elsewhere for the cause of the problem and not fixate on the wires if they pass the identical spark appearance test.

What do the plugs look like? Check them after a good run, coast
to a stop, pull them and take a look. Ideally they should be light gray or tan in color. If they are darker than that - it could indicate fuel problems or ignition problems.

Let me know how your plugs look (this is called reading the plugs) and we can go from there..

BTW - you have checked the obvious - things like the crankcase vent hose - Z shaped hose behind the rear throttle body? These have a 2-3 year lifetime in my experience - and are cheap and fairly easy to replace. I do it every 2 years as part of normal maintanence.

Best,

Don (not MR Eilenberger!)..

Jeremy, have you confirmed that the valve clearances are correct? Hard starting and a rough idle are the exact symptoms my K75 suffered when an exhaust valve clearance was 0.002" under spec.

I agree with Don on the plug wires....the ones on my bike are over 15 years old and seem to work fine.

Don and Jon, good to see you both use this board. I'm currently in exile from IBMWR because I can't figure out how to make Outlook post in plain text. Every setting I can find indicates that it is posting this way, but the list is suddenly bouncing all of my messages. What a pain.

Anyhow, I had disconnected and cleaned the main frame ground, and accidentally left one wire hanging out when I put it all back together. Noticed it quite by accident, but after re-connecting the bike fired up with no problem. Tried to trace the wire and see where it came from, but I quickly lost it. Even with the best diagrams in the world it can be hard to follow those wires. It's one of two brown wires that heads down in the direction of the altitude plug connection.

I'm pretty comfortable blaming the whole problem on this, even though I replaced the spark plugs and air filter after reconnecting the wire. Not a strictly scientific conclusion, but seems plausible to me.

What do the plugs look like?

Click to expand...

They were not tan, more black and sooty up near the firing end. I replaced them in early winter, and shortly after that the folks at Bob's adjusted the air meter bypass screw to enrichen the idle mixture (I was having problems getting the bike going on mornings with temps in the teens; the enrichment didn't help much, ISO-HEET did). I've since had the mixture leaned out, but hadn't cleaned the plugs. I'm inclined to blame the black deposits on this.

On the other hand, there is quite a bit of black muck building up on Cylinder 3's throttle body, especially noticeable around the metal clamps. Also, I was replacing the little elbow hose that goes from the airbox to the plenum and I noticed a film of black gunk all over the plenum. Dunno whether this indicates anything abnormal.

BTW - you have checked the obvious - things like the crankcase vent hose - Z shaped hose behind the rear throttle body?

Click to expand...

Hadn't checked it, didn't know about it until you mentioned it. Feels nice and soft and doesn't appear to have any cracks. Am I correct that the potential problem here would be holes which allow extra air, resulting in an excessively lean mixture?


Jon asks:

Jeremy, have you confirmed that the valve clearances are correct?

Click to expand...

Thanks for the suggestion Jon. The valves were ajusted less than 2k miles ago. They have an interesting history, I might add. I got the bike about a year ago with 16k miles (on an '87!). Took it in for a comprehensive physical, and the valves all passed inspection. Took it back about 6 months later and 4 valves needed adjusting. The tech proposed that either 1) the first guy didn't measure carefully enough or 2) the bike had been sitting a long time developing carbon deposits on the valves, deposits came loose after a bit of regular riding and threw the vavles out of spec.


Anyhow, thanks to both of you. I'm glad I didn't fry something with my careless wiring job.

K75T said:

Don and Jon, good to see you both use this board.

Anyhow, I had disconnected and cleaned the main frame ground, and accidentally left one wire hanging out when I put it all back together. Noticed it quite by accident, but after re-connecting the bike fired up with no problem. Tried to trace the wire and see where it came from, but I quickly lost it. Even with the best diagrams in the world it can be hard to follow those wires. It's one of two brown wires that heads down in the direction of the altitude plug connection.

Click to expand...

I love when it's the simple things! - Eilenberger's Law - LOOK where you last worked.. came true again!

I'm pretty comfortable blaming the whole problem on this, even though I replaced the spark plugs and air filter after reconnecting the wire. Not a strictly scientific conclusion, but seems plausible to me.

Click to expand...

Sounds very likely to me..

They were not tan, more black and sooty up near the firing end. I replaced them in early winter, and shortly after that the folks at Bob's adjusted the air meter bypass screw to enrichen the idle mixture (I was having problems getting the bike going on mornings with temps in the teens; the enrichment didn't help much, ISO-HEET did). I've since had the mixture leaned out, but hadn't cleaned the plugs. I'm inclined to blame the black deposits on this.

Click to expand...

The air bypass on the AFM only adjusts the mix at idle - it has no effect above idle.. the black sooty hopefully will go away with some use - but I've seen sooty plugs on K's that are running just fine, so if yours is running OK - it's a not to worry about it thing.

On the other hand, there is quite a bit of black muck building up on Cylinder 3's throttle body, especially noticeable around the metal clamps. Also, I was replacing the little elbow hose that goes from the airbox to the plenum and I noticed a film of black gunk all over the plenum. Dunno whether this indicates anything abnormal.

Click to expand...

Which hose? The only hose I know of that goes from the airbox to the plenum is the big honking elbow hose (about 2.5" ID)

Hadn't checked it, didn't know about it until you mentioned it. Feels nice and soft and doesn't appear to have any cracks. Am I correct that the potential problem here would be holes which allow extra air, resulting in an excessively lean mixture?

Click to expand...

Sounds like it's OK - but when they go bad (small cracks) you will see some buildup of oil film in that general area. And they make the engine run lean since it is allowing in unmetered air..

Anyhow, thanks to both of you. I'm glad I didn't fry something with my careless wiring job.

Click to expand...

Glad to hear it was a simple thing. The nest of brown wires is always a challenge to get back on right And if you started following them - you'll find a lot of them end up inside the main harness in big crimp/nut connectors where they branch off all over the bike.

Best,

Which hose? The only hose I know of that goes from the airbox to the plenum is the big honking elbow hose (about 2.5" ID)

Click to expand...

That's the one. When I said "little", I was referring to its length.

Replacing it turned out to be quite a pain. Had to get its lip seated around the airbox, then insert the airflow meter (couldn't get the hose seated properly once the meter was in), figure out how to route the meter's electrical cable, then screw the clamps on the hose. Got pretty frustrated for awhile.

Which brings up another question. Even with that wire clip on there, I was able to pull off the airflow meter's electrical connector with only minimal force. Ever seen/heard of the cable coming popping off during a bumpy ride?

I've been trying to figure out what would happen in this event. I imagine the computer would shut down the fuel supply, either because it's programmed to do so if it loses the air signal, or simply because "none" is the appropriate amount of fuel in a no air situaion.



Jeremy

K75T said:

That's the one. When I said "little", I was referring to its length.

Click to expand...

OK..

Replacing it turned out to be quite a pain. Had to get its lip seated around the airbox, then insert the airflow meter (couldn't get the hose seated properly once the meter was in), figure out how to route the meter's electrical cable, then screw the clamps on the hose. Got pretty frustrated for awhile.

Click to expand...

Was there a reason to replace it? I've never seen one go bad..

Which brings up another question. Even with that wire clip on there, I was able to pull off the airflow meter's electrical connector with only minimal force. Ever seen/heard of the cable coming popping off during a bumpy ride?

Click to expand...

Interesting - the wires don't like to come off mine at all.. are you certain the wire clip is fully seated? I have never heard of one coming off by itself (if you think on it - there is no strain on the wire normally, and it's firmly fixed where it goes into the airbox and firmly fixed where it attaches to the AFM.. not likely to come off even without the clip..

I've been trying to figure out what would happen in this event. I imagine the computer would shut down the fuel supply, either because it's programmed to do so if it loses the air signal, or simply because "none" is the appropriate amount of fuel in a no air situaion.

Click to expand...

Never tried it on the bike - I know on a cage with basically the same FI system (old BMW's and some very old Volvos) the engine just stops - later units had a 'limp-home' mode if the AFM failed that let it run - barely, but since the FI system on the early K's dates from the late 70's/early'80's - I doubt if they have this..

Best,

Don

Was there a reason to replace it? I've never seen one go bad..

Click to expand...

It had a bunch of surface cracks and looked pretty crappy; I was just worried about leaks.

- the wires don't like to come off mine at all.. are you certain the wire clip is fully seated?

Click to expand...

Ah, you see through me like an psychic. In fact, I had quite a bit of trouble getting the wire clip seated. One side just never seemed to want to seat properly, so the clamp is really only clamping on one side. Maybe I bent the clamp when I was prying it off to begin with. After about 10 attempts to get it on correctly I finally gave up, figuring all of these failed attemps were wearing down the plastic stubs that are supposed to catch on the clip.

Next big trip is planned for early September. I suppose I'd better try a new clamp before then.

Anyhow, thanks again.