Hi all,
I’ve read all I can and still I am confused. My 1985 K100rt has a poor idle and runs poorly at lower revs.
So far I’ve replaced the following;
Fuel pump and fuel filter. All hoses vacuum and tank to injector rail. Return hose to tank. Fuel regulator. Injectors. Plugs and leads. All electrical connections under tank checked. 
I’ve put a fuel pressure meter on, all ok. 
I have noticed that when I open the oil filler cap I get a idle increase and steady idle. Plenty of suction at the filler cap.
Any help appreciated. My BMW mechanic mate Theo has had a stroke. He kept us running for years. God bless him, I know he would be desperate to help if he could.

How old is your air filter?

Porto wrote:
I have noticed that when I open the oil filler cap I get a idle increase and steady idle. Plenty of suction at the filler cap.

The engine idle should not increase on oil filler cap removal, your test shows that you have AIR leaks. I use Brake cleaner sprayed onto the vac hoses this helps to identify the culprit/s. (Increased idle)

Sign/ symptom's of the z pipe leaking

moriarti wrote:Sign/ symptom's of the z pipe leaking

Easy fix BUT I thought the test on the Z pipe is that nothing is supposed to happen if it is leaking. Hence the question on the air filter age/being blocked. The system is supposed to be sealed.

Point-Seven-five wrote:How old is your air filter?

Check it and if it's ok, check the air intake snorkel for blockage, and if it's ok, check the vane in the air flow meter of the air box to be certain it rotates without restriction and its electrical connector pins are clean and it's tightly connected.

I wonder what happens to the idle when the clamps on the filter box are released and the top of the box is lifted from the filter.  Of course, you are going to do this with the engine running and the oil fill plug tightened.

OThanks for all the help! I’ve checked the Z pipe, it’s good. 
All other vacuum hoses are new. 
I’ve checked all the other suggestions except for putting a vacuum gauge on. I’ve ordered a cheap one e bay and Will do when it arrives.
I noticed today that when I pull off a blanking plug off the any of the first three throttle bodies, all improved in a big way. Any ideas related to this? 
Also Still to pull the air cleaner cover and check while running, Will do when it stops raining.
Porto

Have now also checked around the throttle bodies by spraying WD40 all over. Also sprayed over everything else. No result. Loosened filter cover, no change. 
Will have a look at Airflow meter next.
Thanks.

Wd40 wont help identify your problem, use brake cleaner. You have an AIR leak, go back over what you've done.

OK will do with brake cleaner tomorrow and report back

92KK 84WW Olaf wrote:

moriarti wrote:Sign/ symptom's of the z pipe leaking

Easy fix BUT I thought the test on the Z pipe is that nothing is supposed to happen if it is leaking. Hence the question on the air filter age/being blocked. The system is supposed to be sealed.

CORRECT Olaf , Z pipe is a easy test before pulling things apart,that was my thinking

Checked the Z pipe. It’s good. Has been replaced only a few years back and checks still OK. The only possible vacuum leak would be at the throttle bodies, so will by brake cleaner tomorrow and check it out.

Are you sure that your looking for a leak? Engine picks up RPM and runs smoother when you introduce a leak = rich condition. Leaking injector, air flow door not closing, temp sensor?

Hi Caveman. I don’t think I have a leak. But Walfish thinks I have so will double check. I haven’t checked the temperature sensor or the airflow meter properly. They are on my to do list. I’ll keep ticking boxes as I check. I’m not to certain how the temperature sensor is tested. Can you steer me in the right direction. ?
Porto

Porto wrote:Hi Caveman. I don’t think I have a leak. But Walfish thinks I have so will double check. I haven’t checked the temperature sensor or the airflow meter properly. They are on my to do list. I’ll keep ticking boxes as I check. I’m not to certain how the temperature sensor is tested. Can you steer me in the right direction. ?
Porto

Poor idle and low RPM performance could be caused by many different things or combinations of things. I would do the easy stuff first. Take the air filter out and give the box a sniff of brake clean at idle if the engine stumbles that will confirm you have a rich condition (assuming you do not have an exhaust gas analyzer). Then I would try to balance the throttle bodies (the process suggests that you check valve clearance first) of course at some point you would verify that the spark plugs are good and you have good compression in all cylinders. Point being just checking things randomly or changing parts you may get lucky but more than like just get frustrated and poorer.

Take a look at this thread, post #26 will answer your question.


https://www.k100-forum.com/t12184-still-have-problems-fi-idle-issues

Caveman is correct, the problem is not enough air. 

Question, what are the rpm when stumbling, and what are they when the idle is smoother? 

Check the engine temperature sensor by measuring the resistance between pins #10 and #13 on the big plug that connects to the engine control unit under the seat.  The resistance for a cold engine should be about 2500 ohms, and at operating temperature it drops to about 250 ohms. 

That the idle improves when you pull the air cap off any of the throttle bodies is puzzling.  Pulling the cap should only affect one of the throttle bodies, not all of them.  I would not expect any more than a slight improvement. 

Something between the filter and the throttle bodies seems to be blocking airflow.  The only thing I can think of is the airflow meter and it's idle air bypass adjustment.

What happens when the "choke" on the handlebar is opened? 

Does the engine smooth out when the throttle is opened?

I'm thinking Caveman is right in that the problem is too much fuel, so removing a vacuum cap or oil filler cap allows more air in, maybe the temperature sensor. But not cylinder four is strange. Maybe the vacuum hose is blocked or popped off the regulator. 

If you remove the cylinder four vacuum hose from the throttle body, check for vacuum at the barb, and that the hose is dry. And give it a blip. Any sign of fuel in the hose means the regulator diaphragm is leaking, but unlikely since you replaced it. A vacuum problem would remain regardless of the engine being warm or cold, I spose.

If you remove the vacuum pipe at 4 and fit a vacuum cap instead you dont alter the vacuum or air, but doing so should cause it to overfuel and run rich du to higher fuel pressure. If it doesn't have any effect then the FPR is not doing its job.

Perhaps I misunderstood, when you said removing the first three plugs improved the idle, I assumed that meant removing the vacuum hose from cylinder four had no effect.

daveyson wrote:I'm thinking Caveman is right in that the problem is too much fuel...

I don't believe anyone has mentioned fuel pressure checks - forgive the repeat if they have.  

My 20 year "barn find" ran for crap until I replaced the fuel pressure regulator.  Lots of deterioration in the tank had let crap go down the lines and some of it no doubt wound up impeding the correct operation of the FP regulator.

I did cross reference the BMW part number to a Bosch number, which matched a Jaguar IIRC, and the pressures settled in fine and it runs great - started it after 2 weeks sitting at 25 fahrenheit.

Bill

In the first post on the thread the OP mentions changing the fuel filter and regulator and then checking the pressure and finding it good.

Thanks everybody for your help. I’ve checked everything. With special attention to vacuum leaks, none found using the brake cleaner.
 Also got a few tips of the mechanic near by. He is pretty certain I have several problems. One being the new fuel injectors I have fitted. Two being the noisy new fuel pump I fitted, thinks it’s surging. Three being possible cracked solder joints in the jettronic box. He tells me that it was a common problem with the early cars that used it and that would explain why it is intermittent at times. I still have to check the temperature sensor, and Will do next week. He thinks the suction at the oil filler cap is a blocked crank breather. I pulled the Z hose to check and found that it was hardly breathing. I’m not certain how much it should breath but expect a lot more than it was. Take in mind the mechanic hasn’t seen the bike and is only going if the info I’ve given him. 
I’ll swap the the jetronic with a spare and look further into the breather.

You haven't mentioned a change of temperature sensor but you should be aware 2v and 4v look similar but are very different and not interchangeable. This error happens lots when it comes to buying used ones.

Fuel pressure regulator....2v is 36psi, you have confirmed it is ok.

So....what injectors did you install then? Original in 2v are single hole. I got a set of brand new 4 hole injectors and put them in my 84 RT. They were better ONLY because they were brand new. They increased fuel consumption. Ran them 2,000 miles then put the originial ones all cleaned up back in. I can use the 4 hole ones in my K1100. I sense a possible issue here as there was a tickover issue after I installed the 4 hole injectors but a friend locally [since deceased] went through it and resolved it adjusting/balancing the throttle bodies and sorting out the throttle position sensor but he did say something was off. He sued to be THE K bike tech for BMW locally. 

On the suction the air system is sealed and the only air intake is through the air filter box. The crank case vents through the Z pipe into the air intake and should always be under suction. Pollution control. If the Z pipe cracks it takes air in. If the Z pipe is intact then the engine has negative crank case pressure and will suck like mad once you open the oil filler cap. The only other place it gets air is via the air filter hence a question asked about the air filter. You might need to check the intake pipe that comes from the air box up to the right hand side of the radiator. Hopefully you dont have one of the occasional nests that can arise in that pipe and airbox.

Did you make any other changes? What plugs? Have they an R in the code? If so you need to change them to non resistor plugs.

The comments in things like the ignition control unit and fuel injection control unit are important. Early ones did cause issues and its worth having spares.

I am assuming(dangerous, I know) that the engine runs okay under load at speed on the road. 

If that is true, your engine is starving for air or getting an overly rich idle mixture.  Does the problem appear when the engine is cold?  If it does, look for an air blockage, clogged air filter, blocked idle air flow sensor bypass, or a mouse nest somewhere. 

If the problem comes on when the engine warms up, then the temperature sensor may be at fault.  Check the temperature sensor resistance at pins #10 and #13 on the big engine control plug under the seat.  2500 ohms when cold, about 250 when at operating temperature.

Based on your symptoms, these are the first things I would check.  Opening the oil fill plug is giving the engine an additional supply of air to make up for what isn't coming in through the normal path to correct the idle fuel mix.  Normally, this extra air makes the mixture too lean, but in your situation it is making the mixture better. hence the idle gets smoother.

Thanks for all the good information. I’ve become overwhelmed with it. I’m going to write a list based on all the info and then re check the lot. 
Also I’ve got a suspicion I may have an ignition problem now as well.
Will report back when I’ve got over my depression.

PORTO look on the bright side,you now have so much more info, loads of input from the KLAN, the bike looks good it also starts/runs not perfect but runs anyway, the sun is shining, nobody has died. All in all not a bad place to be, except for that niggling bloody problem you started with  You got to have HOPE

You can help us by giving a little more information about your problem. 

Does it idle rough when it's cold, or when it is warmed up, or is it rough all the time?

Does the engine run properly on the road under load at mid and open throttle?

Does it miss or stumble when accelerating?

Hi all,
Ok so I’m starting fresh. 
This morning I start the K. Instantly fires up smooth, but within seconds starts to run ruff and then die out. Re start not so good and smells rich with black smoke.
I then rig up my fuel pressure gauge between the tank and front injector rail point, as described in Berts instructions. See photo I’ve attached. Result is a whopping 110PSI. 
Please note I have replaced all the lines. Fuel pump and pressure regulator.
I guess I change the pressure regulate again?
Any other test I can do?
PS I get a message saying file can not be uploaded?

Attach a hose to the front barb of the tank, you should be able to blow air into the tank. If you can't, the valve behind the barb is blocked, increasing the fuel pressure.

Or remove the tank filler cap assembly, if fuel is not returning to the tank, that's another sign that the return valve might be blocked.

Or direct the return hose from the front barb into a tank (or return through the tank filler opening) to see if it then works normally.

If it's blocked, remove it and carefully clean it.

Also, the pressure relief valve in the pump is spose to open at about 65psi, but that's only in case of a blockage (this high pressure would explain the loud pump noises) so find the block first and fix that.

Thanks Daveyson. 
Have already checked the return. My one does not have valve, it’s just hole in the barb without restriction. I would say some one removed that part, probably Theo when worked on it. 
I had already checked the flow inside the tank. It didn’t seem to high to me, but then I wouldn’t know.
NOW! What ive done is replaced the new pressure regulator with an old one. Bingo that problem is fixed! Pressure now at around thirty PSI. It go’s up a little when you hit the gas and drops off a little when you back off. And sits steady. Just like in the videos I’ve seen.
Now when I say steady this is providing it is balanced across all the vacuum ports. I do this using a mod that Theo made up for these bikes when he was still working at the shop. If you connect the vacuum from the pressure regulator to intake 4 only as original, the pressure is correct but very unsteady.
Anyway this has rectified everything! 
So, in summary, I fitted a faulty new pressure regulator whilst doing a heap of maintenance. This extremely high pressure was creating both a extremely rich condition and a very noisy under load new fuel pump.
I big thanks to everyone’s input, I appreciate it.
PS I am amazed it managed to compensate for 3 times the fuel pressure.
Porto   

? How do I put pictures up

It varies a bit depending on your computer, I use a phone. 

The second line above where you write your reply, click the first image on the left, then press "select files" then "documents" then select your photo, then  the blue button with the up arrow (or the send all button for multiple photos) then on the second row image that looks like two thought bubbles, then press the send button.

Thanks I will try that. For now this link to a photo page I made may work. 
Some pics of pressure readings and vacuum balancer/filter. It had a drain plug and some sort of collector. I don’t know exactly, I do remember when he was making them. As well as other mods.

https://express.adobe.com/page/2PZw9HuAcCo8h/

Interesting, can you describe your other modifications?

"So, in summary, I fitted a faulty new pressure regulator whilst doing a heap of maintenance. This extremely high pressure was creating both a extremely rich condition and a very noisy under load new fuel pump."


It has become a common problem to assume that just because it is new that it works properly and seems to be more common with "after market" parts. This seems to apply to everything we try to repair in the "just get a new one" world we live in. That is why I love my bricks I think I can keep them running for the rest of my life.

Edit: Forgot to say great to hear you are getting it sorted out, was hoping you would not give up in frustration. Thumbs up.

Porto wrote:
So, in summary, I fitted a faulty new pressure regulator whilst doing a heap of maintenance.

? How do I put pictures up

Please give us a link to the vendor of the regulator and its model number so others could avoid it.

For photo posting, go to the Forum Functionality section and search for photo posting instructions. There are at least two posts describing the process.

Sorry for the delay in reply. Ive been enjoying my ride after all the problems I had. I got the part off e bay, I will look up who from and Post It.
In the meantime Ive learned so much and then applied it.
Relating to my original post. Now when I remove the oil filler Cap the revs stay the same. When replacing the cap I feel the slightest of suction. My research tells me that this is exactly how it should be now. It should always suck a little more than it breathes, and revs should stay stable.
I still have the vacuum across all four throttle bodies using the part Theo made up. I have removed the condensation filter, I think it was just a piece of absorbent material. Not needed, Theo over engineering.
The Bike has not run this well for some time, so I am very happy.
However I do think it could be even better at start up. When I start her up in the morning it fires instantly, and holds 1000 revs with the fast idle on. But it sounds a little ordinary. After a few minutes of idling away I hear a distinct and sudden increase in revs and by now she sounds sweet. Fast idle off and revs at around 900.
I don't have another K to compare mine with. And although Ive been riding her for decades my overloaded brain cant remember if she always like this. What do you experts think. Its a warm temperature  here in the morning
and I am at about 100meters above sea level.

Interesting note: If I put the vacuum back to original on number four and then blank off the rest. The pressure gauge dances all over the place. I remember Theo fitting the part to rectify that problem. Does anyone have any ideas on this. Theo's had a stroke and the question would be beyond him.

The line pressure to the injectors should be 2.5 bar not 1.9 bar.

Thanks mate. Do you think this could be because the non return valve has been removed at some point from the tank return? Or am I back to buying another regulator?

The absence of a check valve in the fuel tank's fuel return port wouldn't cause a drop in fuel delivery pressure.

What was the gain in connecting all four throttle bodies to the fuel pressure regulator vacuum port instead of just one, as the system was designed?

An easy way to check the mixture on 2v Bricks. With a warm engine at the correct idle speed press the green starter button, the revs should not change or increase very slightly if the mixture is correct. If the revs rise the mixture is lean, if the revs fall the mixture is rich. You can then correct the mixture by using an exhaust gas analyser or the lean drop method. Access to the adjustment is I believe 5mm Allen screw which is located under a small rubber plug situated in the top front corner of the air box. Be careful not to tear the plug when removing it, a small screwdriver with rounded off edges helps. A bit of silicone or rubber grease helps to get it back in. How to do the lean drop method is available on this site.
Regards Martin

Thanks Martin, I’ll give the starter button a go at idle when warm and check the results. 
Balancing the vacuum across all bodies steadies out the fuel pressure. I don’t know why but it does. You can see it on the fuel pressure gauge. It was a correction for another problem I think. I have read that I’m not the only cowboy with this going on.

I just thought I would add a not. My fuel pressure is  little low at 1.9 to 2 bar. It jumps up a little when you snap the throttle open and then re settles. I’ve given it a few quick rides and put some demand on it and I can’t see any I’ll effect of the lower fuel pressure. I wonder what the chance is that the e bay China fuel gauge isn’t 100% correct.

Porto wrote:Balancing the vacuum across all bodies steadies out the fuel pressure. I don’t know why but it does.

The throttle bodies are balanced by adjusting their air screws. The use of the vacuum line on one throttle body is to adjust fuel pressure on demand, that one throttle body serving as the index.

Thanks for that info. Doesn’t explain why the fuel pressure gauge goes wild when it’s as per factory. What could that be all about? Any ideas?

Porto wrote:Doesn’t explain why the fuel pressure gauge goes wild when it’s as per factory. What could that be all about? Any ideas?

Does "when its as per factory" mean that the gauge is unmodified, or that it's coupled to the fuel lines correctly?

Is the gauge liquid filled? Who is its manufacturer and what is its model number?

Third time lucky. My post seem to screwing up like my bike.
I have done the starter button test. Pushed it while bike at idle and running temp. The revs go down slightly. So it’s a little rich.
The gauge I used is a cheap one in branded from eBay.
By factory I mean putting the vacuum on throttle body four and capping the other three.
I rode it to work today and it ran very well.