Spark plug collective wisdom

[Eayars]

Here are plugs 1, 2, and 3, respectively, from a 1990 K75S with 52,500 miles. Mileage on the plugs is unknown, since I got the bike at 52,300; but based on the records I have available the bike was not ridden more than 100 miles in the previous 10 years and the unknown owner prior to that was meticulous.

Any collective wisdom on the state of these? #2 and #3 look rich to me; and the bike seems a bit thirsty although I’ve also been fixing gas leaks so I’m not positive about that. #1 looks about right, though. Do I need to start thinking about injectors?

Edit: Turn your computer over if the picture bothers you. I’m uncertain why it’s upside down… but you get the picture.

[Laitch]

What are the spark plugs' model numbers, and what do the electrode gaps measure?

[TriSpark]

Looks like #3 may not be getting any gas, or hardly any. The plugs are D7EA NGK's, right? That's what is in my K75s.

[daveson]

Spark plug one is the best, spark plug three is the worst, and spark plug two is the middlest.

There is a z shaped hose entering the plenum chamber near cylinder three, if this hose is cracked, excessive unmetered air could be entering the system, and so the impact would be worst on cylinder three. This might be the cause of the problem.

[Edward]

clean your injectors. Just send them out to Mr. Injector for a fast turn around of refreshed units. Price is great so no worries about that. If your K sat for that long just do it. Personally, I use iridium plugs. Starting base with clean injectors is just smart.

[Edward]

balance your air intake (throttle body) AFTER installing clean injectors. Reset TPS.

[Eayars]

What are the spark plugs' model numbers, and what do the electrode gaps measure?

The plugs are NGK D7EA.
Bear in mind that the picture insists on posting upside down, so the plugs are 3-2-1 left-right.
3 (blackest) 0.026
2 (middlest) 0.027
1 (lightest) 0.026

[Eayars]

Spark plug one is the best, spark plug three is the worst, and spark plug two is the middlest.

There is a z shaped hose entering the plenum chamber near cylinder three, if this hose is cracked, excessive unmetered air could be entering the system, and so the impact would be worst on cylinder three. This might be the cause of the problem.

Since the picture posted upside down (although maybe it’s showing correctly in Australia?) the order left-right on your screen (with the motorcycle on the ceiling) is 3-2-1. Same answer?

[Edward]

From the moon: plugs are fine.

[Laitch]

Have you been able to do an Italian tuneup or two on that Brick in the 200 miles you've owned it, Eayars? If not, do one for as many miles as you can, then take a look at the plugs. You can brush off the carbon right now.

[daveson]

Yup, 3,2,1. I turned it upside down and assumed 1,2,3.

[Eayars]

Have you been able to do an Italian tuneup or two on that Brick in the 200 miles you've owned it, Eayars? If not, do one for as many miles as you can, then take a look at the plugs. You can brush off the carbon right now.

I’m unfamiliar with the term “Italian Tuneup”. Can you translate to Scots? Is that the equivalent of ‘WFO’ in Suthun’?

Here’s what I’ve done so far:
- Rerouted return hose in fuel tank so it doesn’t just pump gas out the tank vent line
- Tested pressure regulator (it’s ok) and replaced external fuel lines so they stopped pouring gasoline onto the top of the engine
- Replaced front crankshaft seal
- Replaced all fluids and filters
- New tires (BT46, love ’em)
- Replaced front wheel bearings
- Starboard-side bodywork/paint (the bike came with a drop-discount)
- Replaced starboard lighting
- Replaced starboard luggage
- Replaced an assortment of bulbs
- Removed aftermarket brake-flasher circuit that had apparently been installed by drunken lemurs, repaired wiring
- Installed a phone mount/charger
- Adjusted rear brake switch so it actually turned on the brake lamp
- Ridden 200 miles and filled the tank four times.

… Yeah, that last one is annoying. 22mpg on the last tank. This is a vast improvement over the 8mpg I got while the fuel pump and leaky regulator hose and misguided in-tank sealant application were conspiring to happily pump $6/gallon California gas out in a smelly flammable trail behind me everywhere I went, but I was really hoping for closer to 40mpg.

New injectors are on order… At this rate, the $3,000 F800ST I passed on as ‘too expensive’ in favor of this K75S is looking like a damn good deal, but I’m hopeful that I’m running out of things to fix.

[Edward]

Don't fret over the plugs; it's no big deal. Once the injectors are installed, the throttle bodies are balanced, and the TPS is reset, you should have a more even burn and better gas mileage. There really wasn't any need to buy new injectors instead of having the existing ones cleaned or refurbished, but many people do the same thing, regardless of the bike's brand. When you had the tank off, did you clean the screen at the bottom of the fuel pump? Tip: Installing quick-disconnects on the fuel lines helps tremendously when removing and reinstalling the tank.

[Eayars]

It’s not the plugs I’m fretting about, it’s 22mpg and I think the plugs are indicative of the problem. There is also a gas smell on warm restarts (and it acts flooded) so I think probably the injectors are not closing entirely and the FI rail is depressurizing through injectors 2/3. I’m pretty sure I know what’s going on, but this is my first “modern” BMW (haha) so asking experts… Thanks for the help!

Oh, and quick-disconnects. Brilliant, thanks. Recommend a brand/source?

[Edward]

I'll take a look at my records and snap a photo of the setup when I'm more awake.

[Edward]

installed early 2023 without any problems to date. Smartest modification other than suspension and full floater conversion.

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