Hello, I have just recently purchased a 1991 K1 with 47,000 miles. I replaced the spark plugs, spark plug wires, all fluids, front fork seals, fuel filter etc... After getting the bike together and started, the bike seems to develop a missfire regardless of RPM's. It sounds as if there is some sort of "mechanical slack" (bad description) when the missfire happens. Nothing I've ever heard before on any other bike.

I'm at a loss of what it could be? I'm familiar with the airheads/oilheads but not the K bikes (first one)

Any potential ideas of what could be wrong would be greatly appreciated! Thanks!

possible injector spray pattern - sticky ness issue ?

may need to get them cleaned ...

1 - Check that the spark plug leads are all firmly seated on the spark plugs. If you're using OEM leads then they should not wiggle at all.

2 - If you have a butane/propane torch then spray some unlit gas around the boots between the throttle bodies and cylinder head. If the idle goes up then one or more of those boots is cracked and leaking.



Regardless if that solves your problem or not, remove the ignition amp from the front left corner of the battery tray and refresh the heat sink compound. The most ignored/unknown maintenance item on these bikes. If that heat sink compound is not keeping the ignition amp cool then the bike will not run as well as it should.

If the bike has been sitting for a long time the injectors may be varnished up.  Get a bottle of Techron Fuel System Cleaner and put some in your tank.  Run the engine for five minutes to mix and circulate it through the system.  Let the bike sit overnight and run it again for five minutes the next day.  Continue doing this while you work on other stuff on the bike.  After 4-5 days any varnish in the injectors should be cleaned out.

Thank you for the responses everyone! I will try some of your recommendations out.

Hi,

to this forum!


Bernie

p.s.: when replacing the spark plugs, keep attention that you will use ones with "SAE-Plugs". Without this little parts it could be, that you have no correct ingition.
look also here for an example:

forum.kforum-tech.com/members-upload/uploads/Zuendkerze_mit_SAE_Mutter.doc

Welcome! Good luck with the K1.

Well, no luck on it running any better. I ran the bike in the dark to see if I could see anything and noticed that you could see detonation from the top of the throttle body every time it missfired. I've never seen anything like that. So something is not causing ignition at the proper moment I suppose?

What exactly do you mean by 'see detonation from the top of the throttle body'? Is there a split in the rubber?

Nsdean03 wrote:Well, no luck on it running any better.

Which of the suggestions made here did you follow—all of them?

I've attempted everything but checking the heat sink compound involving the ignition amp. Instead of using Techron I used Liqui-moly fuel injector cleaner.

So where the throttle body and intake tube attach, there is clamp. When running the bike, a missfire will occur. When that missfire happens you can see a flash under the clamp on the second throttle body to the left. It's hard to explain so I apologize for being confusing. There are no splits or tears in the rubber.

Is this flash above or below the throttle bodies ?

Nsdean03 wrote:I've attempted everything but checking the heat sink compound involving the ignition amp.

Cleaning the ignition amplifier and applying heat sink compound (heat paste) can be an important element in preventing misfires in the 4V models like yours; its condition should not be ignored. It is located on the battery holder. The compound is available at Napa, Pep Boys and other parts stores. BMW uses Curil K but the others get the job done. See if you can decipher these instructions from a K1/K100RS 4V manual.

Laitch wrote:

Nsdean03 wrote:I've attempted everything but checking the heat sink compound involving the ignition amp.

Cleaning the ignition amplifier and applying heat sink compound (heat paste) can be an important element in preventing misfires in the 4V models like yours; its condition should not be ignored. It is located on the battery holder. The compound is available at Napa, Pep Boys and other parts stores. BMW uses Curil K but the others get the job done. See if you can decipher these instructions from a K1/K100RS 4V manual.

I got mine at Radio Shack. (Before they closed most of their stores.)

I just scrape off all of the old stuff with steel wool and then apply a new coat.

Made a noticeable difference when I refreshed it on my 91 K1.

If it gets bad enough it will kill the bike after a few blocks of riding. (similar symptom to a failing HES)

charlie99 wrote:Is this flash above or below the throttle bodies ?

Above

duck wrote:

Laitch wrote:

Nsdean03 wrote:I've attempted everything but checking the heat sink compound involving the ignition amp.

Cleaning the ignition amplifier and applying heat sink compound (heat paste) can be an important element in preventing misfires in the 4V models like yours; its condition should not be ignored. It is located on the battery holder. The compound is available at Napa, Pep Boys and other parts stores. BMW uses Curil K but the others get the job done. See if you can decipher these instructions from a K1/K100RS 4V manual.

I got mine at Radio Shack. (Before they closed most of their stores.)

I just scrape off all of the old stuff with steel wool and then apply a new coat.

Made a noticeable difference when I refreshed it on my 91 K1.

If it gets bad enough it will kill the bike after a few blocks of riding. (similar symptom to a failing HES)

Ok I'm going to give that a try then. I'll laugh when the only thing I didn't try was the problem. Thanks again guys!

Misfires are more often due to malfuntion of the Hall effect sensor(s). The sensor itself or the cooked wires. Due to the age of these parts, it's very common today that they're faulty.

You may not think the rubber is split, but I'll wager that it is. Did you try the butane trick?

Dai wrote:You may not think the rubber is split, but I'll wager that it is. Did you try the butane trick?

Yes, and no changes. Very strange

Don't forget to check the hyperspatial quasiturbo reverse deconfabulator. (Bosch stole the design from Lucas.)

duck wrote:Don't forget to check the hyperspatial quasiturbo reverse deconfabulator. (Bosch stole the design from Lucas.)

Ah yes, I almost forgot about the hyperspatial quasiturbo reverse deconfabulator, how silly of me.

Nsdean03 wrote:Ah yes, I almost forgot about the hyperspatial quasiturbo reverse deconfabulator, how silly of me.

You won't forget it again after you've spent four hours using the Q-tips, ethanethiol, bulb syringe and emesis basin to take care of it if refreshing the heat paste doesn't work.

Moved to Technical Repair & Troubleshooting, from Member's Intro, because, well it should have just been a member's intro with questions asked later and in the section for such posts...but you know how the bar room sometimes gets noisy when a new drinker walks in.