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bmwmyplace
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Australia
Joined: 02/26/2007
Posts: 168

Posted this on the Kradrider site , thought I might put it here also

Ive been playing with the carb on the R12 , as I said before it seemed to be running lean on the idle jet... I changed the whole carb over to another one but it made little difference, I then checked some jets on a third carb and noticed that the idle jet had be played with in that it had been soldered and redrilled or more likely redrilled too big then soldered up aand drilled again, so I put that one in and now it starts very well and even idles like a BMW should.

I took it for a half hour run but noticed it tends to miss a little on acceleration, Im thinking thats its on the transition jet? perhaps Ill play with that one tomorrow see if I cant drill the next jet out a little , Also I think I need to advance it a little more as it starts ok on half retard not at all on full retard and very well on full advance. I seem to remember when I timed it that it was half a tooth out and the sproket only had one keyway in it, so Ill have to find another or make it. It would be nice if someone made some with vernier ajustments like some of the very early brit stuff. Or I could leave the key out all togeather but that can let you down sometimes.... hmmm things to play with

NOW BIG FAVOUR time I am attempting to put a Chang Jiang sidecar on the bike and the front fitting is all wrong for my application I was wondering it any one would have some photos of the front lower sidecar mount . I notice that the some have an adjustable bent tube others have a straight tube solid welded on

my email is gibbsp at bigpond.net.au

Many thanks Peter

Peter D. Nettesheim
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VBMWMO #5744
Joined: 01/27/2006
Posts: 128
R12 tuning and more

BMWMYPLACE,

Here is what you need to know. I have tried many combinations of different jet sizes on the R12. I made a table of the jet size and running results. I experimented with different combinations and finally arrived at a terrific combination of jets giving a smoth transistion from idle to part load to full load at sea level. I then compared the results obtained to the sizing the factory recommended. Much to my dissappointment, they were exactly the sizes the factory manual indicated (I thought I was going to "fine tune" my bike to run better than the factory could come up with).

I am assuming you have the manual with the proper jet sizes and you have confirmed they meet these standards.

This is where you need to start. Then we can go on. Quite frankly, I don't think you problem is with carburation at all, but first tell me you have this straight.
One more thing. If you can , put a brand new set of plugs in the bike (not just cleaned ones!!) and tell me if it runs any better at all and transistions better (not perfect) through the different stages of idle, part load and full load. If it does, it indicates a different problem than the carb. Lets start with this though.
Regards,
Peter D. Nettesheim
bmwmuseum@hotmail.com

bmwmyplace
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Australia
Joined: 02/26/2007
Posts: 168
Tuning R12

Hi Peter I agree if they manged to make thousands of these things they surely would have been reliable....and from written accounts I belive they were

I have two sets of jets 30, 65 and 70 they they are from 74 OZ carbs 1940 (and the heads are also 74 OZ for what its worth ) and they look unmolested but I cant tell for sure , i intend to buy a set of number drills (or metric equivelent) as I only have odd ones and see if I can use them as a guage to compare the jets that I have,.... the other three have been fiddled with,

I have faced all the flanges and used gasket cement with the gaskets, I have listened (with a piece of PVC hose as stethoscope) for sucking sounds around the joints, I have sprayed aero start around the joints, I dont think there are any air leaks.

I have ordered a new set of plugs and will get them tomorrow I will inform you of the result

Thanks again for responding Kind Regards peter Gibbs

bmwmyplace
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Australia
Joined: 02/26/2007
Posts: 168
Tuning R12

Now to the problem I think you have with your ignition that you think is the carburetor.............. well not everything at once......

well you are probably right I went to the auto parts store and bought two W8AC and two W7AC plugs got home put one of the W7AC in went two the other side and discovered that the nipple on the plug was not removeable...B...ger so took them out and put the W8AC's in started first kick both cyclinders Smile rode it up the road 500 mts went well then stated to miss on aceleration it was better on full throttle ( just a little sqirt as not run in yet) rode it aroung up and down the street for about 20 minutes it also seemed to "hunt" when holding it in second or third.. returned home took out the plugs ...BLACK and sooty. I then noticed that there was some considerable condensation on top of the carb and inlet manifold. ?

And no I do not yet have the heater tubes conected, like many things I bought from Poland they dont fit.

I did have a bugger of a time at setting the timing at first until I
discovered that my magnetos for the R12 are slack wire advance,
different to my Brit bikes, so when I thought I was advancing it to
do the timing I was infact retarding it ... Derr. I think I have it
sorted now though.

the other issue if I can remember correctly when I set the timing I seem to recall that optimun was half a tooth out , and the sprocket I have only has one keyway , I was tempted to leave the key out but didnt and as a result I probably have a slightly retarded ignion,

Having said that when it comes up to the VZ mark the points just break so I guess its up to you Maestro perhaps you have some pearls that will bring it back into tune....hopefully

Big Grin Kind Regards Petrer G

Peter D. Nettesheim
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VBMWMO #5744
Joined: 01/27/2006
Posts: 128
Probably right??

Probably right.......?

Well, I couldn't resist. I guess its the German in me. I think its that same attitude that got Germany in trouble in 1939........

more later.........

Peter D. Nettesheim
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VBMWMO #5744
Joined: 01/27/2006
Posts: 128
R12 running

Pete,
I have a moment so I thought I would give you a bit more to consider. First, it is difficult to advance in how to address the running situation untill you get the bike as close to proper settings and equipment as possible. You need to get the preheaters hooked up and make sure the jetting is correct.
I am suspect of the ignition and this is why I asked you to install new plugs and see if it ran better. You indicated it did and they quickly sooted and then running deterioated. A strong ignition will typically overcome this situation. To explain:
There is a range of fuel to air mixture that will ignite. If the mixture is too lean or too rich the mixture won't fire. The ratio which is typically considered optimal is approx 14 to one. If you could measure the mixture out of the R12 carb as it feeds the increasing RPM of the engine you would find that it varies at different flow rates. So at idle it might be 14 to one and then above idle 14.8 to one than when the engine is a bit faster it might be 12 to one and so on. If the mixture has great swings due to improper jet size, carb wear, improper float setting...and many other possible errors, the fuel air ratio will swing outside the "bandwidth" of the plugs ability to fire it.
Now here is the key: If the ignition is weak the bandwidth is narrow and minor swings will become un-firable (is that a word?). This is what I suspect the problem is.
Quite frankly, I had the same problem so I figured I would let you avoid the struggle I went through. Do you understand? I hope this helps.
Peter D. Nettesheim
BMWMUSEUM@hotmail.com

bmwmyplace
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Australia
Joined: 02/26/2007
Posts: 168
Tuning R12

Peter Thanks for taking more time I will take all this on board and give you an update as I go.

Kind Regards Peter

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