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Autor Thema: Idle Air Adjustment R25/2  (Gelesen 594 mal)

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Kurt in S.A.

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Idle Air Adjustment R25/2
« am: 28 Juni 2020, 19:27:08 »

Carb is 1/22/44.  I'm thinking I might not have the idle air mixture set right.  My Bing manual says the setting is 1-1/2 turns out.  Does that seem right?  Usually that's a starting point, though.  How does one go about fine tuning that?  Do I get the engine warmed up and change the number of turns in (cuts out some air to make richer) and out (lets more air in to make leaner) and find the spot where the RPM goes the highest?  Maybe then a slightly bit richer from that point?

Thanks...Kurt
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Idle Air Adjustment R25/2
« am: 28 Juni 2020, 19:27:08 »

Hans Otté

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Re: Idle Air Adjustment R25/2
« Antwort #1 am: 28 Juni 2020, 20:42:01 »

Carb is 1/22/44.  I'm thinking I might not have the idle air mixture set right.  My Bing manual says the setting is 1-1/2 turns out.  Does that seem right?  Usually that's a starting point, though.  How does one go about fine tuning that?  Do I get the engine warmed up and change the number of turns in (cuts out some air to make richer) and out (lets more air in to make leaner) and find the spot where the RPM goes the highest?  Maybe then a slightly bit richer from that point?

Thanks...Kurt

Hi Kurt,
the values you are mentionning seems to be right, my docs are saying same.
But do any basic adjustments to the carb's settings only when the engine is in good working condition and really warmed up.
Oel temp should be stabilised around 70 to 80° to get an stable idle. A short ride will get the engine to that point.
HansO

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Re: Idle Air Adjustment R25/2
« Antwort #2 am: 28 Juni 2020, 21:02:25 »

Thanks, HansO.  I'm more comfortable doing something like this on my R69S or my /7, although on the /7 I'm controlling a gas circuit, not air.  Also in those cases, I'm trying to balance the two cylinders...I still seem to only have the one on the R25/2!   ;D

Kurt
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Re: Idle Air Adjustment R25/2
« Antwort #3 am: 28 Juni 2020, 23:58:35 »

....and find the spot where the RPM goes the highest?  Maybe then a slightly bit richer from that point?
Exactly like that !

Cheers,
Sascha
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Re: Idle Air Adjustment R25/2
« Antwort #4 am: 29 Juni 2020, 19:22:33 »

Just checked...the adjustment was at about 3/4 to 1 turn out.  So, I reset it to 1-1/2 turns out.  Will need to final adjust at the next ride.

Kurt
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Re: Idle Air Adjustment R25/2
« Antwort #5 am: 29 Juni 2020, 20:00:16 »

Just checked...the adjustment was at about 3/4 to 1 turn out.  So, I reset it to 1-1/2 turns out.  Will need to final adjust at the next ride.

Kurt

Hi Kurt,
when there a solution has been found, eventually a problem may be solved !
But don't forget : one resolved often means two new ones will propperly appear, soon.
Be happy, don't worry and good luck,
Hans
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Re: Idle Air Adjustment R25/2
« Antwort #6 am: 29 Juni 2020, 21:03:40 »

Well, you're probably right.  I'd posted about this before, but one issue that had been bugging me is some popping of the exhaust when I close throttle to shift gears.  I checked valve clearances last week and found them good, except that the intake was a bit tight...I like to run it at 0.15mm...exhaust was 0.20mm where I had left it.  The ride this past weekend showed the popping to be quite reduced, although I highly doubt that such a small change was the reason.

The other thing that I'm trying to resolve is that the engine surges a bit when running in lower gears at slow speeds in the neighborhood.  I was wondering if maybe my idle jet was too small...I don't know precisely if it is the 35 called out in the specs...it's been a while.  Then I thought about the mixture setting and how it might be affecting part throttle running.  I understand that the regimes of carb operation - idle jet, needle jet, main jet - all overlap at various throttle positions.  So, I'm trying to get the carb set where it should be and go from there.

Kurt
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Re: Idle Air Adjustment R25/2
« Antwort #7 am: 02 Juli 2020, 19:31:37 »

Hi Kurt,

find the setting as described. then make a test: try to find a "mountain road" an let the bike roll on high revs downwards. If the setting is too weak, there will be "bangs" to be heard in the muffler. Too, if the washer between exhaust and cylinderhead is worn out.
You will see, that there is a very small turn between "too weak" and perfect.

Good luck,

Jan
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Re: Idle Air Adjustment R25/2
« Antwort #8 am: 02 Juli 2020, 19:49:27 »

right, lean mixture can cause the popping. As leaks in the exhaust also can do.
One other potential cause are the ignition-advancer-springs.
If they lost tension over time, the fly-weights need lowers revs, until they swing back to their "late" position - the ignition is advanced although it isn't supposed to.
To check this, remove the generator lid, connect a strobe gun and aim on the advancer. Works best in a shaded or dark area.
Now rev it and watch the weights while closing throttle and rpm drops.
If they don't swing back till shortly before idle-rpm, it maybe worth a try to renew the springs.
But I suppose there will be an improvement already by setting idle more rich.
Next step could be to lift the needle one position - enrichens the next regime above idle. If required.

Cheers,
Sascha
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Re: Idle Air Adjustment R25/2
« Antwort #9 am: 02 Juli 2020, 20:09:23 »

Sascha -

In the position I found it, the idle mixture was screwed in too far, shutting off air making the idle circuit more rich.

The surging around the neighborhood at slow speed seemed to begin middle of last year when I lowered the needle from the 3rd to the 2nd position.  Ever since I got the bike, the mileage was around 50 mpg (US).  I felt it should have been better than that.  So I made the "crude" adjustment with the needle.  Now the gas mileage is more like 63 mpg.  I spend most of my time on 2/3-3/4 throttle so I'm likely on the main jet as well.  I was thinking that the needle adjustment might have affected the low range idle circuit.

I'll have to consider the advance springs...they might be original for all I know!!

Kurt
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Re: Idle Air Adjustment R25/2
« Antwort #10 am: 19 Juli 2020, 15:35:49 »

Well, today was the day to get the bike out to warm it up and then come back and adjust the idle mixture.  And that's where the fun begins!  I had left it at 1-1/2 turns out.  I loosened the lock nut and turned the screw many turns each direction...I heard no change in engine RPM.  Hmmm.  Guess something is plugged.  Prior to this the screw was less than 1 turn out.  On today's ride, the popping on gear up shift when I roll off the throttle was virtually gone.  I still had the minor "hunting" after the ride and I was slowing heading back to the house in the neighborhood.  So, I decided to turn the screw 2 turns out and will see how it runs next time.

--- update --- As I think about it, if it didn't make any difference when I moved it with engine running, resetting it to 2 turns out probably won't make any noticeable difference.   :spinnt:

Kurt
« Letzte Änderung: 19 Juli 2020, 17:43:53 von Kurt in S.A. »
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Re: Idle Air Adjustment R25/2
« Antwort #11 am: 20 Juli 2020, 14:23:26 »

Hi Kurt,
sounds like something other then the mixture screw is limiting/adjusting your idle-rpm.
Not sure what is stock on R25/2 - but check, if the mixture (idle-air) screw has a longitudinal bore with 2 tailings beneath a little tin cap.
Maybe this is clogged and prevents proper setting.
See this thread, post #19, pic #7 
https://bmw-einzylinder.de/forum/index.php?topic=16214.0

Cheers,
Sascha
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Re: Idle Air Adjustment R25/2
« Antwort #12 am: 20 Juli 2020, 17:05:42 »

Sascha -

I'm typing a second time...tried uploading a picture that was already on the forum.   :(

Anyway, I don't have that little "cap".  I'm familiar with this on my R69S.  In the link below, look at the first picture.  I don't see how there's any room to fit a cap on it.  I thought the cap was more or less a crude filter to keep debris from getting into the hole that is on the screw.

https://bmw-einzylinder.de/forum/index.php?topic=18077.0

This is the way the bike came to me.  I might just back the screw fully out and examine it more closely.

Kurt
« Letzte Änderung: 20 Juli 2020, 17:08:42 von Kurt in S.A. »
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Re: Idle Air Adjustment R25/2
« Antwort #13 am: 20 Juli 2020, 18:18:03 »

Hi Kurt,
seems there are two different screws available, a short and a long one. Whereas the short is assigned to R24.
Check this out:
https://www.ulismotorradladen.de/artikelliste/Vergaser_Luftfilter_BING_Ersatzteile.aspx?BildNummer=V030
both versions displayed on that site. --> "Gemischregulierschraube"
Looks like you got the short one, thus no room for the cap.
No Idea, if the carb works as intended with each of them.
The explo shows the long version including the cap - parts 30,31,32. Which is correct for R25/2.
Position the mousepointer onto each particular part in the explo until it's highlighted, then click.
Will display the german term, order-number and price in the right window.

Regards,
Sascha
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Re: Idle Air Adjustment R25/2
« Antwort #14 am: 20 Juli 2020, 18:52:42 »

Interesting.  I wish all companies used the same part numbering!!  When I look at my Bing manual, the R24 had the T77 carb while the R25-on carb was the T115.  Further notice that the parts you're pointing to on the R25/2 carb are identical to those on my R69S carb (T120).

I'll have to take out my short screw and see what's going on.  I suppose I could "borrow" the set up from my R69S and see what the difference might be.

--- When I look up the parts on the Benchmark Works site here in the US, they list the following:

13 11 0 039 180----carburetor idle mix screw Bing R24-R25/2 R27

That seems to suggest that there's only one screw used for all the singles.  Something's not right here.

Kurt
« Letzte Änderung: 20 Juli 2020, 18:59:01 von Kurt in S.A. »
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Re: Idle Air Adjustment R25/2
« Antwort #15 am: 20 Juli 2020, 19:21:14 »

the Explo covers different models, see Title: "Vergaser + Ersatzteile, Luftfilter:R24-R69S"
= Carb and Sparparts, Aircleaner...
So its like a general example for Orientation.
Concerning the part-numbers you were absolutely right.
Recently I learned my lesson here: Rabenbauer.com uses original BMW Part-numbers.
So you can spend the nightime to cross-check against other dealers via Searchterm, Drawings and sketches, until you are halfway sure, to order the desired part ;-)
I never heard the carb-model-terms you mentioned. Maybe it's something BING-internal.
But it's common, that many parts are equal among different carbs. As e.g. the main jets.
Also in my link it says for the long screw: "Gemischregulierschraube für BMW R25-R69S, lang", so there's nothing odd with it.
Borrowing the parts from your Boxer is what I'd do first.

Sascha
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Re: Idle Air Adjustment R25/2
« Antwort #16 am: 24 Juli 2020, 00:30:38 »

I happened to go to Mark Huggett's site and see that for the R25/2, they're calling for the shorter idle mixture screw without the "cap".  On this page, it's part #26 on this page...part 13 11 039 180...click on the "info" letter on that line to see the picture.

https://www.bmwbike.com/index.php?e=mhs#nav-sub2

Mark shows that beginning with the R25/3, the longer screw was used.

I haven't tried removing the current mixture screw on my bike but will get to it.  When I do, I'll also pull the air cleaner and then spray some brake cleaner in from the mixture screw side and see if there's anything coming into the carb throat.

Again, there's conflicting info depending on where one goes to look.

Kurt
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Re: Idle Air Adjustment R25/2
« Antwort #17 am: 31 Juli 2020, 17:07:47 »

I checked with Bing here in the US and they confirmed that my carb should have the longer screw with the sleeve and cap.  So, I have that ordered and now installed in the carb.  Have set it initially at 1-1/2 turns out.  Before installation, I squirted carb cleaner into the hole and the liquid came out in the throat of the carb so that lets me know that the orifice is clear.  While I had the air filter...er "rock strainer"...off, I went ahead and cleaned it and put another coating of gas/oil on the mesh.  I used a 10/1 mixture of gas to oil...the gas evaporates off leaving the oil behind.

I'm anxious to give it a ride to see what kind of difference it might make.

Kurt
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Re: Idle Air Adjustment R25/2
« Antwort #18 am: 31 Juli 2020, 17:49:53 »

an anxious Texan - from San Antonio - secret heart of the Lone Star State -surely, yes of course.
Now tell me you are shy !   ;D
C'mon, Remember the Alamo !  :attacke:

Sascha
« Letzte Änderung: 31 Juli 2020, 18:18:28 von 4Taktix »
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Re: Idle Air Adjustment R25/2
« Antwort #19 am: 31 Juli 2020, 19:04:56 »

We're not shy here!  Texas was the only state to have been under six different national flags!  We got around!!

Kurt
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