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Barry Robin
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VBMWMO #52
San Francisco, Ca.
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here's a quick one for those with R11/12's with Sum carbs:

i replaced the float and it's idling fast...
the brass float bowl-what direction does it go?; the dome towards the top or the bottom?

senile dementia at it's best!

Peter D. Nettesheim
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float position

The Dome is up! Your fast idle is another problem not caused by this.

Barry Robin
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VBMWMO #52
San Francisco, Ca.
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which way is up for floats?

i was afraid you'd say something like that. any suggestions on where to start looking?

Darryl.Richman
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Surf City, USA (Santa Cruz, CA)
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which way is up for floats?

There's not too many things to play with.

Do you have an air leak somewhere? Maybe the throttle cable is bound up and holding the slide off the stop?

I had to have a new slide made up because mine was so loose in the bore, it rattled. And I couldn't get it to idle at a consistent (slow) speed.

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Barry Robin
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which way is up for floats?

i probably have leaks everywhere! time to check the sealant.

the cable seems to be ok-i never feel it binding up on me. and the idle speed is usualy consistant untill i started fiddling with the float-and of course i still need one that doesn't fill up with gas.

just in case, i'll reset the idle screw,in case someone fiddled with it while it was parked somewhere. you never know...

damn; i wish there were someone who rebuilds and restores these things.

Darryl.Richman
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VBMWMO #6285
Surf City, USA (Santa Cruz, CA)
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which way is up for floats?

It's pretty much the blind leading the blind, and I hope to be in your spot in a couple months. Right now I'm building a wheel so the frame straightener can use it as a guide. Then it will be paint. Meanwhile, the engine bottom end is sitting in my garage. The cylinders have been bored, but my machinist didn't like the chrome top rings that came with the new pistons, so am waiting on those. Then the cylinders go to the powder coater. Hopefully I will be able to build the other wheel in this time.

As far as restorers go, Vech builds these bikes. He probably has the most experience of anyone on this side of the pond.

And Peter, who had two of these bikes at the BMW MOA rally last month, has been very gracious with his time and knowledge. It's just that it's so difficult to diagnose these kinds of problems over the net.

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Barry Robin
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which way is up for floats?

well, it looks like a leaky float's the least of my problems; the throttle slide-or the cable-is binding up on me, making it difficult to set the idle.

and: i'm not getting full power lately when i use first gear-it doesn't want to pull without lots of gas; am i right in assuming that my timing is retarded or my points need adjustment?

and if so, is there an easier way to do it that the old jiggle the points and hope for the best routine?
what's everybody been doing to time these prewar sidevalves? it's not like there's a manual-in any language! and no timing marks, either...

Darryl.Richman
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which way is up for floats?

I couldn't set the idle on my bike when the slide was loose in the bore. It created a variable air leak, and the motor would accelerate and decelerate over a few seconds. I had a new slide made from brass that fits closely and setting the idle was no problem after that.

I'm not sure about manuals for an R11, but I believe in the timing areas it should be the same as the R12 or the previous generation R52/57/62/63 bikes, and there are English language manuals for these bikes. Craig Vechorik has the manual for the R12, and I have a (very faint) copy of the other one.

Also, there ARE timing marks, but they are present for setting up the motor when it's out of the frame. There are two marks on the back side of the flywheel, OT and VZ. OT is top dead center and VZ is the full advance mark. Each has an arrow and there's a witness mark on the crankcase. What I have done, based on comments from Craig Vechorik, is to add my own witness mark to the window below the right cylinder. Then, line up the OT mark with the witness mark on the flywheel and back of the case, and add a new OT mark on the front of the flywheel where it lines up with the new witness mark. The same for the VZ mark. With this change, it's possible to use a timing light on the motor.

Since your motor is already in the bike, you'll have to do it the old fashioned way. The basic plan is to set the advance lever (or twist grip, if that's how your timing is set) to full advance, find OT on the compression stroke for the right cylinder, back the motor up to the VZ mark, and set the points to just openning at this point. With this relationship, you can use the lever/twist grip to retard the spark to whatever point works best for you, and not worry about advancing it too far for the motor.

On an R12, the VZ point is where the piston is 8-9mm before reaching the OT point. I believe, but have not double checked, that this is about 40 degrees before tdc. Also, be sure to back up the motor beyond this point and then move forward until you reach it, so as to remove all lash from the timing gears.

And yes, it does require removing the head from the cylinder in order to measure this distance.

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Barry Robin
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VBMWMO #52
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which way is up for floats?

uh-oh!...lots of detail that went over my head!

thanks for the helping hand. i've just printed out your instructions in the hopes that a mechanic can just follow the directions.

but if nothing else, i just ordered am R12 manual from vech; even if a mechanic doesn't read german, the specs alone should be easy to suss out.
i looked around for one for an R57/63 in english, but i could seem to find anyone who sells it; ah well, one victory at a time...

-b

Bruce Frey
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VBMWMO #6316
Texas Hill Country, USA
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Timing

I have an English R12/R17 Handbuch in PDF as well as a reprint that I got from Huggett.

The electronic copy is probably too big to send by email, but I can pull out the pages where it talks about timing.

If you send me your email address I would be happy to send you the pages you are interested in.

Best regards,

Bruce

Darryl.Richman
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which way is up for floats?

Similarly, I've scanned my R52/57/62/63 manual (and parts list) into PDF files, the former is 3.5Mb and the latter about 6Mb. If you send me your email address, I'll send either or both.

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Bruce Frey
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Timing

Interestingly, there seem to be several different R12 ignition timing numbers floating about:

English Handbuch Illustration: 1/4" - 19/64" (±6-8mm)

English Handbuch text: 8-9mm

German Handbuch Illustration: 5-6mm

German Handbuch text: 7-8mm

R12 Data Sheet: 42 degrees, 12mm (I checked this mathematically and 42 degrees does work out to be ±12mm)

I THINK all the numbers are in the same context.

Cheers,

Bruce

Barry Robin
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which way is up for floats?

thanks for the offer, guys! feel free to just click on the email logo below my post to get a hold of me. if that isn't working, my address is: barryrobin@aol.com

the thing is with my timing problem, is that as the timing was set only about 500 miles ago-when the engine was rebuilt-i keep thinking that this is a points only situation; that i might just need to find top dead center and gap the points (assuming they're not fried).
two things: when i pull in the spark advance, the engine dies, and yesterday it was only firing on the left cylinder. i figure that the spark is now already so retarded that the advance just shuts it down...

does that sound about right?

too bad that there's no vintage club member or mechanic in ireland or england to go to-but if you know of one in england i might be able to truck it over to him.

sending it to vech from ireland will be a tad pricey, i'd think!

Darryl.Richman
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which way is up for floats?

Barry, I know there are a couple Brits on the Kradrider list (a list for WWII German bikes) who have R12s or are interested in them. I seem to recall Drew Grant lives in Northumbria, and Anthony Evans (not sure where exactly).

I sent you the scan of the owner's manual; hope it helps you.

Regarding points, a magneto bike should never erode the points, unless the condensor is dead. (Unfortunately, if the condensor is dead, you have to R&R the whole mag, as it's buried inside.) If the condensor is dead, the bike will not rev well and you'll notice quite visible arcing across the points when they open. It's easy to see with the bike running in a darkened garage, with the cap removed from the points chamber.

If one cylinder dies, then it's likely that there's something wrong with that cylinder. The valve settings might have come loose on one of the valves; I would check that first. (I've had this happen a couple times and the cylinder runs crappy first and then doesn't run at all.) I've also had a pretty new Bosch plug quit working -- that will do it, too. Wink

Bruce, that's very confusing news. I noticed the measurements on the timing diagram in the R12 book. I also noticed that they're different between the R12 and the R17. However, in my edition of the english manual, dated October 1936, the text agrees with the diagram (says 7-8mm). The spec for the R17 is 12-14mm.

Craig Vechorik has said that he transfers the timing marks from an R50/2 to the R12 flywheel and has good success. I believe the F mark on an R50 is at 39 degrees btdc (and the static timing mark for idle is at 9dbtdc).

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Bruce Frey
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which way is up for floats?

You should receive an email shortly with the R12 info. If you don't belong to The BMW Club of UK and Ireland, you should consider it. They have a vintage section.

Peter Dunn, who is also a member of this club, should be able to point you towards someone. There is a fellow by the name of John Lawes who is knowledgable about plunger frame bikes (he is also a CJ dealer), but I don't know if he knows much about the previous generations. I have heard of another fellow by the name of Harvey from another group who sounds as if he shoud be avoided.

cheers,

Bruce

Darryl.Richman
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which way is up for floats?

Barry, it also occurs to me that you might find Erik Bahl's website helpful. He restored an R12 and took a lot of photos from beginning to end, and produced a very useful description of all the work he did.

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Barry Robin
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which way is up for floats?

i know eric's site very well-i'd check in most every week to see how he was getting on with the R12. sort of like a must-see t.v.show, i'd eagerly await each new episode...

funny thing: i just back from taking it out through the dublin streets, and it performed beautifully! it pulled just fine, idled fairly correctly and did everything the way it's supposed to. too bad it might not tomorrow. sometimes it feels like a freind who goes off their meds occasionally-you never know what you'll get.

thank to both you and bruce for the pdf files; they'll come in more than handy.
i think the next step is to either rebuild the carb or to swap it over to a dual carb system using those re-pop grazins from ebay...

Peter D. Nettesheim
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timing mystery resolved.

Gents,
I have been away from the forum otherwise I would have put my two cents in earlier. The set up of the timing is simplistic in theory and operation. First you need to avoid tying to use knowledge of later BMW timing. The exact method is laid out in the R12 manual (which is available in english). This is the process:

1)Set either cylinder to TDC (do you know how to determine which cylinder is at TDC?).
2)rotate the engine in reverse direction to its normal operating rotation till the point where the piston is at a distance from the top of the cylinder the prescribed amount (I don't have this figure off the top of my head but can easily find it in the manual if necessary. I have only seen one dimension for the r12 and the spec on all sport machines is different). In addition, all this stuff about precise 7mm or 8mm is insignificant. Why? Two reasons. The timing of the engine is based upon the precise position of the timing advance mechanism, which varies and you have not even addressed the fact that the timing will likely be in perfect position when the chain cannot even be placed over the sprocket on the front of the magneto. Are you aware that there are two different magneto timing sprockets to take up for this varience (don't tell me you have both types in stock). Don't be hung up on precisely 7 or 8 mm since quite honestly I don't believe you will be capable of getting it to within even 3mm.
You won't need to anyway to get proper performance.
3)set the magneto so that the points are just opening when the timing advance ring is at full advance.
4)Here's the one people forget. You must now remove the ignition wire from the magneto on the side that is to get spark and confirm you see a small brass strip on the backlite distribution ring otherwise your timing will be off by 180 degrees. Do you understand? Both plugs do not fire at once!
5) Shim and then install the magneto for proper chain tension.
6)If you have done the above correct, you can forget all about the timing marks on the flywheel and the rest of that BS. The above is exactly how the factory has given instruction and all the rest is just extra information of no importance.
Good luck and write me at BMWMUSEUM@HOTMAIL with any questions.
Peter D. Nettesheim

Peter D. Nettesheim
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One more thing

Your carb issue should be easy to resolve. Start by installing new jets of the proper size. Let me know the results and we can pick up from there.
Peter D. Nettesheim

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