2021 Drake Smith - Please do not use or reproduce this elsewhere.  Feel free to link to it though.

K Bike Fuel Injectors

All BMW K bikes are fuel injected.  Unlike most cars, many times, for various reasons, K bikes will sit unused for extended periods of time. (As in years, not months.)  When this happens, the gasoline left inside of the fuel injectors will dry out, leaving non-evaporable "varnish" inside of them.  These deposits can cause reduced flow, impact the spray pattern or even clog them completely.

Given their construction, it is generally not possible to clean fuel injectors at home.  The proper way is by placing them in a heated cleaning solution in an ultrasonic cleaner.  This gets out all of the varnish and restores them to the correct spray pattern and flow rate.

(Generic picture. These are not K bike fuel injectors.)

When should I have my fuel injectors reconditioned?

Since you never really know a bike's history when you get it and, given how old these bikes are getting, there's a good chance that any K bike you purchase has probably sat for an extended period at some point in its life.  Therefore, whenever I take possession of a "new to me" K bike, I have the fuel injectors reconditioned to ensure that the bike is running as well as it can.

Is there a recommended service interval for this?

Not really.  However, I usually give my bikes a complete stem to stern servicing at every 50,000 miles and do this as preventive maintenance.

Where can I have my fuel injectors reconditioned? (USA)

I send mine to Mr. Injector.  I just wrap them up, put them in a USPS small flat rate box with the service form and away they go.  I've tried other retailers who perform this but have settled on Mr. Injector because:

  • The price is reasonable at only $18 per injector with return Priority Mail shipping for about $8.

  • Quick turnaround time. He usually only has them for a day or so and with Priority Mail shipping both ways you get them back quickly.

  • His service includes a report showing before and after testing of the spray pattern and flow rate.

  • Included are new O-rings, filters and pintel caps for all of the injectors.

  • They are cleaned up or painted if necessary.

As a point of reference, here are the before and after results from a 59K 1986 K100 that I purchased in the summer of 2013:

The results Mr. Injector sends back with your FIs look different than this. The above is a spreadsheet that I put together when I got them back.

Removing Fuel Injectors

1.

Pick the small wire clips off of the electrical connector for each fuel injector. Then pull off each connector. Reinstall the wire clip on each connector to keep from losing them. When you put the connectors back on, the wire clip will just slide over the angled nubs on the side of each injector.

 

2.

Loosen the hose clamps (7mm socket or flat screwdriver) and remove the fuel lines at the front and rear of the fuel rail. Note that if the bike has been run recently there may still be pressure in the fuel system so turn your head to keep gas from spraying into your eyes.

 

3.

For K75s and 2V K100s: There is a small well in the cylinder head around the base of each injector. Using compressed air or a small vacuum, clean around the bases of all of the injectors.  If you do not then any dirt or tiny pieces of gravel that have collected there may fall into the cylinder head when you remove the injectors. (This is not an issue for 4V K bikes as the injectors are mounted in the rubber boots between the throttle bodies and cylinder head.)

 

4.

Remove the two 10mm hex bolts that attach the fuel rail to the cylinder head.

 

5.

Pull the fuel rail with the injectors straight back. It's not a bad idea to stick something like rolled up paper towels in the fuel injector ports when the inejectors have been removed.

 

6.

Remove the square clips that hold each fuel injector in the fuel rail and then pull each injector out of the fuel rail. The clips just pull off to the side pretty easily.

Installing Fuel Injectors

1.

Coat the top and bottom O-rings of each fuel injector with a light film of motor oil or other lubricant.

 

2.

Insert the top of each fuel injector into the fuel rail, making sure that each one is fully seated. Once each injector is seated in the fuel rail, reinstall the square clip that holds it to the fuel rail.  The inner face of the clip should be seated in the slot around the body of the fuel injector and the outside slots should be on the lip of the fuel rail port.

 

Pictures:

 

Square clips that hold tops of fuel injectors into the fuel rail: (may be silver in color on earlier Ks)

 

Groove in top of fuel injector for the clip:

 

Fuel injector seated in fuel rail:

 

Clip partially installed:

 

When the clip is fully installed the lip on the rim of the fuel rail port should pass through the slits on each side of the clip:

 

3.

Install the fuel injectors into the cylinder head. Sometimes on K75s and 2V K100s the injectors may be a little stubborn going into the cylinder head fully.  If this happens, I usually place a block of wood on the fuel rail and then hammer lightly on the fuel rail or I use a rubber mallet and GENTLY tap the fuel injectors into place until they are fully seated.

 

4.

Reinstall the two 10mm bolts that hold the fuel rail to the cylinder head.

 

5.

Reseat the electrical connectors on each fuel injector.  Give a quick pull on the BODY of each connector to make sure that it is properly seated.

 

6.

Reattach the two fuel lines and tighten their hose clamps.

 

7.

Start the motor and let it run for a short period. Inspect for leaks at the tops and bottoms of the fuel injectors.

Ongoing "Maintenance"

It doesn't hurt to add some Chevron Techron Concentrate to the gas every now and then. Auto parts stores often have Buy 1 - Get 1 Free deals on it so that's a good time to buy it.

 

It's a good idea to resynch the throttle bodies any time you replace the fuel injectors, install new spark plugs or adjust the valves.

2021 Drake Smith - Please do not use or reproduce this elsewhere.  Feel free to link to it though.