R25 Idles Ok coughs at higher revs

[Ligarosa]

Hello friends,
I own an R25 and have the following problem.
The engine struggles at high engine speeds and emits a noticeable gasoline odor, backfires and emits black smoke. The carburetor has been inspected and appears to be functioning properly. However, a broken advance-retard spring and a loosely fitted capacitor were discovered. Additionally, the ignition points produce visible sparks even in daylight  .
Most likely, due to continuous electric arcing, the contact points have developed a greenish discoloration.

I have the following questions, if you know:
How to check if the capacitor is "alive" and in case it is not, to replace the capacitor, is it necessary to disassemble the entire advance-retard unit? It appears to be screwed in from the back of the plate.

For timing adjustment, is there an alternative method besides using a strobe light?

Does the greenish discoloration on the contact points also require their replacement?

[Ligarosa]

[strichzwojan]

There are definetely problems on the electric side, but can be on the carburettorside too.
Dismount the adv/retarding-unit, replace the condenser and the points.
Look closely at the mounting of the flat spring and the condenser-cable. There must not be any contact to minus/earth!

At the end of our starting page, there are downloads of the owners manuals. Read it carefully.

Good luck, Jan

[Heiko]

... and if you done that, check if there is a temporary loose connection in the ignition lock plate in the headlight.

Anyway, I don't think it is a problem with the carburator.

You can also advance the ignition by clamping the adjuster to "advance" with a wire and then adjusting it statically.


Regards, Heiko


PS: Where do you live?

[rolf]

wackeliger Zündschlüssel kann es nicht sein?


kann ich nicht übersetzen

[Taz]

As Heiko mentioned (and Rolf meant to specify further)...there might be an intermitting contact at the circuit board in the headlight housing, possibly a "dancing" ignition key (characterised by fine idling and missing ignitions at higer revs, caused by a slackened contact at the circuit board and a key with worn grooves for the securing balls)...

easy to confirm: rev the engine up, when the issues show press down the ignition key while keeping the revs at the same level...if the symptoms can be "switched" on and off by pressing down the key the addittional few thous or releasing it again you have found your culprit.

solution 1: remove the circuit board from the headlight to allow full access, fix the contact tongue, then put it back together (generally not recommended as the circuit board is fixed in place by twisting some steel "tongues", these snap easily and will thus cause further, nasty work to be carried out.
solution 2: take a spare key (you don't want to mistreat your original one, do you?) and weld a little spot on the tip, extending it by 4-8 thou (or 0.1 to 0.2 mm)...that will do the trick until the headlight nousing is overhauled completely someday...

[cledrera]

Your Translation Sir:

wobbly ignition key can't be?

[Eppo]

How to check if the capacitor is "alive" and in case it is not, to replace the capacitor, is it necessary to disassemble the entire advance-retard unit? It appears to be screwed in from the back of the plate.

For checking the capacitor there are some fine tools made by Prüfrex (you wil find some information here in the forum about them).
A strong visible spark between the contact points of the interruptor indicates that there is something wrong.
Maybe some broken capacitor or a bad electrical contact.

Because of the low price for a new capacitor, most guys replacing them (or have always one spare on in stock).

Replacing the capacitor is a real challange, as you mentioned, you have to remove the advance-retard unit and the mointing plate of the interruptor to reach the screw heads of the capacitor, cause these are lokated from behind the mointing plate. Before removing the mointing plate make some marker line so it is much easier when replacing.

Because of the bad quality of new capacitors it can happen that even new ones won't last long till the first failure (this happen to me in the past) and to make the changing of the capacitor much faster and easier I replaced the capacitor by using a self made braket on a different position.

Here you can find my small diy procedure for a new capacitor placement:
https://bmw-einzylinder.de/forum/index.php?topic=21307.msg322406#msg322406

Btw: It is always kind to have a small introduction of yourself when coming here for the first time (like who you are, where you're from and how you get in contact with BMW and of course some pictures of your motorcycle might be nice)

kind regards

[rolf]

Your Translation Sir:

wobbly ignition key can't be?

  

[strichzwojan]

Und wieder mal ein Treaderöffner, der nach dem Erstellen seines (ersten!) Beitrags und den vielen Fragen, die da kamen, nicht wieder vorbeigeschaut hat...

[rolf]

diese typen liebe ich

[Einzylindär]

Künstliche Intelligenz....

Gruß
Stefan, der Einzylindär

[Eppo]

Künstliche Intelligenz....

Gruß
Stefan, der Einzylindär

Könnte sein, muss aber nicht. Ich hab gehört, dass es noch Länder gibt, wo Leute nicht permanent im Internet sind  .

Wobei ja auch KI immer raffinierter wird.
Vielleicht sollten wir diesbezüglich einfach einen Verhaltenskodex einführen:

Wenn hier Fragen als erster Beitrag kommen, ohne eine kleine Vorstellung zu beinhalten, dann ist der erste Beitrag dazu aus Höflichkeit nicht auf die Frage zu Antworten, sondern erst einmal zur Person zu interviewen 🤷.

Klar wird man es damit nicht aufhalten, aber durch Fragen kann man schon gut herausfinden, ob jemand Ahnung hat oder nur irgendwas vorgauckelt.
Geht bei Schwätzern auch.

MfG

[Ligarosa]

Hello, sorry for the absence but serious issues kept me away. First of all thank you for the responses, pretty helpfull!

I replaced the broken advance spring and now trying to find a way to tighten the capacitor (lots of sparks). I manually earthed it and it seems to work, but I will try to get a new one connect the positive and earth it with a wire to check for improvements.

Obviously I am not AI

The bike belonged to my late father and after some "experts"  paid help finally I am trying to make it functional on my own.

[Heiko]

Anyway... where do you come from?

[Ligarosa]

@Heiko I am from Greece.

[andreas kontogianis]

where from Greece my friend?
regards Andreas

[Ligarosa]

@andreas kontogianis I live in Crete

[andreas kontogianis]

i live in Amorgos
call me maybe i can help you..6942805221

[Heiko]

@andreas kontogianis I live in Crete

Great... next Forum meeting there! 

[Ligarosa]

@andreas kontogianis Thanks, i will call you nexr week

[Ligarosa]

Small update: I made a small adjustment—swapped out the capacitor—and noticed some improvement. However, something odd happened: I took a ride and later realized I had forgotten to install the idle air screw (engined died in idle, expected ). When I put it back, the engine idled as expected, but now it chokes at high RPMs—though not in the same way as it did with the old capacitor. The spark plug is completely black, which suggests the engine is running too rich. I recall seeing a post describing a similar issue, but I don't think there was a clear solution. Any thoughts on what might be causing this?

[Heiko]

Check the timing of the ignition. If it is correct take a smaller
mainjet or lower the needle in the carb one notch. Testrun and then feedback here.

[Ligarosa]

Hello, I am back! The ignition timing lamp has arrived and I conducted a small test: The S mark on flywheel is ok in idle, but the F mark appears on the upper side of the inspection hole.

Given the S mark is ok and the ignition advance is regulated by the springs on the advance unit (correct me if wrong) that means that there is an issue with the advance retard mechanism (springs or whatever)?

The F mark should stay in the center of the inspection hole for any revs above the ones it appears?

[Kurt in S.A.]

I'm not sure that the springs are the total control for the advance.  The springs adjust the rate of advance, but I think there should be a hard stop with the advance unit.  So that should be checked.  I wonder if one could dial back the S-mark such that the F-mark returns to the center of the window?  That might compromise the starting of the bike.  Curious?

Kurt

[Kees]

S is not so important, it'll start with a slightly late ignition just as well (of course it shouldn't get beyond OT). F is the important one. But I don't think that explains the coughing at higher revs. It would make cause pinging.

These advance units wear in all parts and that gives increasingly earlier timing at the F-mark. Does your advance still have the limiter spring, a small leafspring mounted on top? Or is it broken? That is also a common issue.

[Ligarosa]

@Kees s You mean a part like this?

[Kees]

Yes, there are two versions. The one you show is the newer one, the older one is like this:


You could try do double up those springs, that would limit how far the advancer advances.

[Ligarosa]

As far as I can tell the spring looks ok. I wonder if there is just to much fuel from the carburetor that floods the cylinder, if we take into account the fact that it works better with the idle mixture screw removed.

@Kees do you mean to use rwo springs?

[Kees]

Yes, two springs on top of each other. That's a tip I read on the American forum.

[Kurt in S.A.]

Those two bent springs look like the ones used on the twins starting in 1955.  I have something similar on my R69S along with a "stop bolt"...I won't go into that now.  But on my R25/2, there are no such springs.  The plate of the advance unit needs to have a spot to install those springs...I don't see anything like that on my advance unit.

The counter weights that are part of the advance unit have vertical posts that run in tracks.  Eventually the posts will hit the end of the track and stop advancing.  And the base of the two coil springs in the advance unit can be adjusted to increase/decrease the tension in the two coil springs.

Kurt