Tried to start but . . . .

[PrintTech]

I'm looking for some guidance with my K100. I managed to get it running yesterday albeit without any real power. I've replaced the fuel pump, filter and lines to the injector rail. I've also replaced the injectors, battery and a blown fuse for the pump. I've been inside the air filter box looking at the airflow meter. The valve is suppose to be spring loaded so I'm guessing it should rest in one spot to start. I find mine seems to stick in one direction. I've moved it while I had the engine running only to discover that stops the engine. Has anyone any idea as to what's considered normal??

Thank you!!!!

[Kaos]

Well, thats a part you really shouldnt we willing and wanting to be fingering, but I reckon everyone has their thing.
Anyway. The flap itself is quite sensitive and should be easily movable and always return to its base position on its own.
Not doing so could result in poor or bad performance.

If it's sticking or binding—not springing back easily—that’s abnormal and will cause significant running issues, including lack of power, cutting out, or stalling when the flap is moved while running, sticking in a position would send false data to the ECU with al troubles accompanied by false data.
Basically when you fingered your flap, you told the bike it had  massive airflow resulting in a bad fuel air ratio, thus killing the engine.

So for troubleshooting:
The flap should move "very freely with no friction at all" when gently nudged by hand, returning to a closed/rest position under light spring tension..Any physical sticking, hesitation, or irregularity points to a problem, such as gummed-up pivots, a worn clock spring, or internal contamination/damage.If manipulating the AFM flap kills the engine or causes abrupt changes in running, it strongly suggests the AFM is either dirty, has electrical contact issues, or the spring mechanism is faulty

[Laitch]

The valve is suppose to be spring loaded so I'm guessing it should rest in one spot to start. I find mine seems to stick in one direction.

In addition to Kao's observations, the temperature sensor installed in the AFM's opening should not be dirty. Also, clean the AFM's electrical connector and be certain it firmly couples with the unit. I don't recommend going beyond that right now unless its vane action is obviously defective.
The two most common problems with severely neglected Bricks are poor electrical connections and excess air leakage into the fuel intake stream from degraded rubber intake components including the z-tube crankcase breather. Reducing the chance of poor electrical connections requires cleaning the main ground connections on the frame backbone and cleaning all electrical connectors with electronic cleaner. The four-pin connector linking the fuel injection relay to the fuel pump often creates intermittent failure from poor connections.

[PrintTech]

To Kaos and Laitch:

Thanks for the tips!!

The vane is getting stuck. I know that because I was moving it to see if one position got it running. It did. I got it to idle with the choke on. Gentle throttle got it to 5000 RPM at one point. But that was yesterday. Since then I can get it to fire, but it won't run well enough to idle. I've been going through the air intake. The inside of the AFM is clean, as is the sensor. I could feel it bind when I tested the spring back motion. Time for a replacement?
I also know that leaks in the rubber bits is a bad thing. I looked them over. The crankcase breathing tube is a mess and the rubber tips on the throttle bodies are cracked, no doubt leaking! I'm also reasonable sure the timing is off. I have a timing light but not one I can adjust. Which plug syncs to the mark on the crank? On the K75 it's #3, don't know about the K100. Any suggestions for locking that down? Gotta dig the light out as I haven't used it since my '70 Triumph GT6 needed a tune up!!

[frankenduck]

I wouldn't bother with the timing light. Just make sure that the Hall Effect Sensor notch is aligned and the timing will be fine.



I used a timing light once on a K and all it did was confirm that the timing was fine. I've installed several Hall Effect sensors and when aligned with the notch the bikes ran fine.

[Laitch]

I'm looking for some guidance with my K100. I managed to get it running yesterday albeit without any real power.

Fiddling with a timing light or aligning notches won't make an engine run any better if its fuel mixture is too lean. Eliminate excessive intake air as the culprit. Because the engine will idle, use a thin stream of volatile carb cleaner, unlit Mapp gas or unlit propane and aim the gas around each throttle body intake from top of the intake to the bottom of the throttle body. It the revs increase the components should be replaced.

If the AFM is moving stiffly as you describe you could use AFM cleaner to see if that will get it back into smooth action.

[PrintTech]

Unfortunately the AFM's stiff movement is a result of the moving part (what I've labeled the vane) scraping the housing. I've been trying to see if I can get it to free up. I don't know if the point it pivots on is bent or if the case it sits in is deformed.  My fear is that it will have to be replaced. With the line of work I'm in, with something like this I'd take it apart and work through it. But the fact the screws are sealed means there is more to this than simply "opening it up".

I'll try the gas tip around the intake provided I can get it to idle long enough.

As they say, I've got nothing but time so . . .

As for the timing - I love setting it to a reference point and letting it go. The thought of a hall devise doing the timing is interesting. Most of the Hall devises I deal with are for counting or marking transition. We use optical sensors for timing as they are accurate to thousands. However this is 40 year old technology so - I get it!!

Again - thanks for the tips!

[PrintTech]

So I pulled the AFM. To me it looks like the pivot is bent.

[Kaos]

I looks somewhat of axis, yes. But i am unable to determine if that's because of the light, maybe lens angle. A "healthy" flap looks a tad bit off as well.
However what it does show is that it doesnt completely shuts.
IMG_20250930_171136.jpg (29.32 kB . 569x576 - viewed 270 times)

[Laitch]

  Most of the Hall devises I deal with are for counting or marking transition.

That's what the Brick's HES is doing. I recommend that you read the manual at the link I described. It is unnecessary to use intuition to understand what's going on although I suppose it's intellectual exercise.

It looks like the AFM works have been damaged by an impact—probably a drop onto a floor somewhere—that has affected the function of the vane and could have even affected connections of the air temperature sensor. It's difficult to determine whether there is corrosion on the opening's left side of your Brick's device or it's simply an image artifact. Consider replacing unit. There are usually a few on eBay. The air flow meters from K100 2V or K75 have the same part number at Max BMW's fiche so either should be a suitable replacement

[PrintTech]

Laitch, still working on navigating a forum. I did not see the link but I'll look again. Thank you!

In the meanwhile - I took the AFM apart. Not working in it's current state so . . . .
 


This is under the black cover. With a multimeter I should be able to verify the thermocouple is working. The resistance should change as the temperature changes. Same with the resistance as the vane moves. Not touching the springs and other mechanicals as that would be asking for trouble!

The bottom cover was a bit more problematic as it is sealed nicely! However . . . .



I could see where the vane was scrapping the cover. A little work got it moving freely.

The only question (other than will it work?) is about the channel paralleling the main port. It has an adjustable screw at the end that no doubt meters air flow through it. In the meanwhile I'm not moving it.



One thing I do know is when I try to start it sometimes it backfires pretty hard. As the plugs are old I'll pick up a replacement set to see if it does better.

[Laitch]

Go here; scroll down to the LE Jetronic Training Manual.

[PrintTech]

THANK YOU!!!! BTW, I finally got mine running today. It won't idle but it will run. Hopefully replacing more worn, tired rubber bits squares it all away!!

[Laitch]

It won't idle but it will run.

A functioning AFM is needed for idle.

[PrintTech]

After reading the LE Jetronic document it is making more sense! Thank you! I have been working on mine to get the sensing flap to move freely. It works well until I close the cover. Cleaning up where I see it rubbing is slowly showing results. Once it's moving freely I hope to see some positive results.
I do have a question about the fuel tank pressure relief valve. Every diagram I've looked at shows it connecting to the crankcase. I have yet to see where it does this. Mine is currently hanging free. Where does this connect?? This poor bike was pretty neglected by the last owner.





I'm sure these are no worse than what most others have found.

Again a big thank you to all pointing me in the correct direction!!!

I now have a running engine - never mind there are still more issues to address!!

[Laitch]

I do have a question about the fuel tank pressure relief valve.

Use circles or arrows to mark the subjects in your photos, as Arlo Gurthrie described way back when. I'm uncertain if I'm seeing what you're describing. The main subjects in your photo are the crankcase ventilator z-pipe and the fuel tank vapor hose with an inline pressure valve.

The hose with its inline valve in your photo was connected to a small metal pipe protruding from the crankcase surface on the right side of the radiator—looking from the front of the Brick—near the radiator standpipe. That small pipe should have been stoppered with a secure rubber cap, or a hose with a bolt in it. The hose I see in your photo has a pressure relief valve in it. Remove that valve before it sticks closed and causes pressure problems within the tank. Run the hose to exit below the right foot peg.

What is seen below is the timing chain case cover beneath the location where the radiator would be mounted, and the crankcase coolant standpipe to its right. The crankcase vapor inlet is to the left of the coolant pipe.

[PrintTech]

OMG!!! Yeah, that I see! Some one must have felt it needed a screw in it! Thank you!!!



So yesterday I had a working fuel pump today it is DOA. I'm back to the wiring. Fuse is good, so I'll follow the voltage.

Again, THANK YOU!!

[Laitch]

OMG!!! Yeah, that I see! Some one must have felt it needed a screw in it! Thank you!!!

That will do it if it doesn't leak.

[frankenduck]

Since that's capped on the front of the engine you might want to get one of these:

https://www.kbikeparts.com/classickbikes.com/ckb.tech/0.ckb.tech.files/thecup/thecup.htm

[PrintTech]

I like that! Those lines are indeed a pain to put back!

Next project is to drain the radiator in order to replace the cooling fan. It's now missing three blades as it slowly self destructs! Got the project running long enough to ride it around the block. Interesting as this morning the fuel pump wouldn't go. I was so pissed I left the bike on the driveway till the afternoon. I then tried it again and the pump was working. If it is once again not working in the morning it's back to troubleshooting. Gotta love a challenge! That or I'm just a mental case!!