K100 low rpm problem HELP

[Hooter]

Greeting fellow MOA members. I need a bit of tech help.

I have an 88 K100LT, 55,000 miles in good condition. Here is the problem.

Sudden low RPM power and performance. I crossed a warning strip on a highway and the trouble started. The big has poor power and misses below 2000 rpm. I have checked plug wires, plugs, fuel filter, pump, air filter, etc. Nothing out of sorts. Above 2000 RPM bike runs with no problems, good mileage, power, and temperature is normal.

The problem reminds me of the older cars with a bad vacuum advance for the spark timing. I have checked and cleaned the FI computer connection but not the iginition module.

I do have an open vacuum port on the bike and I don't know what if anything is connected to it or it it left open to air or blocked off. Looking at the left side of the bike, under the fuel rail there is the idle adjustments and the vent hose that is covered by a spring i believe that comes from the crank case. To the left of this hose is a locking adjustment screw and this open port. It looks like a hose should be on this port. It is about an 1/8 of inch in diameter and is open to air. There is a vacuum at this port. What goes on this port? I think something was knocked loose when I crossed this warning strip.

Any help on this would be appreciated.
Thanks in advance.
Hooter in Tennesse

 

[jdiaz]

The hose with the spring comes from the fuel pressure regulator, so it needs to be hooked up.

 

[JohnHall]

I had the same symptoms on the exact same bike. The vacuum ports should all be covered. You can order some of the small rubber caps. Mine sounded like an old diesel and when I covered the port with my fingertip....instant smooth idle.
BTW your oil cap can have the same effect if too loose or accidently left out.

 

[deilenberger]

On your K - there are 4 vacuum ports. One on each throttle-body, one for each cylinder. The rearmost one is where the fuel-pressure-regulator (FPR) hooks up. That's the hose inside a spring. The FPR lives on the back side of the throttle-body-assembly.

The other three vacuum ports (located at the same spot on each throttle-body) should have rubber caps on them.

If the hose is disconnected you have way too much fuel pressure and the bike is running rich. If one of the vacuum ports is missing the rubber cap - that cylinder is running lean at low RPM (it has less effect on the mixture at higher RPMs).

Please clarify what you're seeing (a photo would be helpful..)

 

[Hooter]

Clarification on BMW trouble

Thanks to all the members that have replied.

The hose covered by the spring is secure and on the vacuum port that it should be on.

The vacumuum port for the rear cylinder is open. I will cap it off with the proper size plug and check the other 3 cylinders. I think this will probably solve the problem.
Thanks, and I will report back on this.

Thanks,
Hooter in the hills of Tennesse.

 

[breyfogle]

....The hose covered by the spring is secure and on the vacuum port that it should be on. .... The vacuuum port for the rear cylinder is open.

It probably does not make a difference with how the bike runs but the regulator hose with the spring attaches to the rearmost TB.