I think I found the problem

[bgcameron]

This '90 K75S is my first K-bike, and I have not had it for very long.. I was a getting poor gas mileage, despite it seeming to run quite well. I decided to check the valve clearance and the spark plugs. Valves were mostly within tolerance, with #3 exhaust being at .24 mm. #1 exhaust is a little loose at .33 mm but that shouldn't be a problem.

Now- spark plugs. I am led to believe that these plugs need terminal nuts. I think these things were arcing!


The plug wires look pretty old, and the insides of the caps are full of rust and crud. I will be ordering a set of wires from Bob's BMW. I realize now that the bike DID seem to take a while to warm up while using the throttle advance. I am used to carbs so I didn't give it too much thought. Hopefully getting a good spark will make a big difference on the bike.

[The Mighty Gryphon]

NGK are great plugs.  I have used them for nearly 50 years with no complaints.

Now, first off, the #8 heat range is a step colder than the #7 recommended for the brick engine.  No big deal as long as the nose of the plug doesn't get too black with carbon buildup.  Still, if I was troubleshooting a mixture/tuning issue, I would probably want to use the recommended heat range.  Does your engine run hot?  A lot of knuckleheads think that running a colder plug will make a hot engine run cooler.  It doesn't.  It just lets everyone else know how ignorant they are.

The problem here is that the D7EA and D8EA don't come with terminal nuts.  You can go to a small engine repair place and ask if they have any old plugs with nuts you can take, or you can contact NGK Canada technical support and ask if they can send you a couple sets of terminal nuts so you can continue using NGK plugs without having to switch to another brand.  Tell them you are having misfire issues and spark burning of the terminals.  Send one of your photos with the email.  They sent me a dozen for my bikes for free. 

You can reach them at: https://www.ngksparkplugs.ca/

Another option is to use the DR7EA resistor plug.  For some reason, these plugs are supplied with the terminal nuts, and there is no problem with using a resistor plug with the BMW resistor wires.

[bgcameron]

Thanks for the response. These are actually the DR8EA plugs. I went to a local parts store and they have the DR7EA but they don't come with the nuts. I'll keep looking for the non-resistor plugs. Worst case scenario- I pay a few bucks more at the dealer!

[The Mighty Gryphon]

Contact NGK, they are pretty good about getting the nuts to you.  I'd ask for a dozen.  Then you don't have to worry about them.

[Laitch]

I'll link this question with the topic.

Will vegan entrées be on the menu at your inauguration dinner, President-elect Mighty Gryphon, and do you know whether bgcameron bought the Enduralast spark plug wires from Bob's BMW or the OEM wires?

[bgcameron]

I'll be getting the inexpensive ones..

I have a question about the timing chain tensioner. While turning the cams to check the valve clearance, I noticed a slight amount of movement in the tensioner. Is this taken up by oil pressure when the bike is running?

[Scott_]

Yes, it is supposed to be.
At the top of the chain tensioner mechanism there is a small hole where oil is supposed to be able to escape and lubricate the underside of the chain as it goes across the rail. Sometimes this hole can get plugged up. The tension mechanism still works, however the lack of lubrication to the rail can cause the 'wear strip' to prematurely wear out. Something to inspect if you have the timing case cover off.