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norwaybike
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Joined: 01/26/2007
Posts: 37

Hi!
I have a 1938 model R12 military with Bing 1/24/12 carburetor and the original military air filter. No choke function...

Problems are starting the bike. I have correct and good spark plugs, can easy change the ignition point for later (retard) and good compression. Even with repeated "tickle" the carburetor, kicks without ignition and different positions on gashandle the bike will not start. It may seem like it is not going fuel to cylinders. The plugs are completely dry even after repeated attempts. I take a little start gas and sprays directly into the cylinder through the plug hole, insert the plug and try and have start attemt on the cylinder.

I suspect simply that the gasoline not come to the cylinders, and perhaps a little narrow mixture. After 15-20 minutes attemting the bike starts and runs perfectly.
But even when the bike is hot I often struggles a lot to start.

Anyone have some experience with similar problems??

Best regards, Frode

mdunn
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VBMWMO #9044
Riverside, CA
Joined: 02/21/2008
Posts: 87
You have a Bing on this bike?

You have a Bing on this bike? You don't have a SUM? Is it two bings carbs or just one? One of the biggest issues with a bike not pulling gas into the cylinders is vacuum and weak intake gaskets. This is one thing, another is not enough fuel in the float? Lets start with the basics, do you have new intake gaskets? Is it a good seal from the intake to the carb?

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norwaybike
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Joined: 01/26/2007
Posts: 37
Yes, I have a Bing on this

Yes, I have a Bing on this bike. As far I can see a correct type, and perhaps used on some R12. (http://www.faak-tillmanns.com/shop/u/TVI/BMW_R_12_1-24-12-Horizontal.pdf) Mine is vertical.

When I started the restauration it was both a Bing and SUM With the bike, but the condition on the SUM was bad.
It is only one Bing, and a manifold.

I think the intake gaskets is in good condition. I have used "startgas" in actual area when the bike runs (idle) to hear if the speed on the engine increase. But nothing happens with the speed. It seems to me more or less the same amount of fuel is still in the float after several kicks at the starter. I can see this when i "tickle" the carb, and gasoline come out of the overflow immediately. No smell of gasoline or wet at the sparkplugs.

Perhaps the smartest thing to do is start dismantel the carb and have a look if I can see some obvious problems.

Best regards, FRode

mdunn
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VBMWMO #9044
Riverside, CA
Joined: 02/21/2008
Posts: 87
The correct carb for a single

The correct carb for a single R12 is a SUM, NOT A BING. Are you aware you can purchase a new SUM that works perfect? I have installed them on over 5 different R12's now and never a problem with the new SUMS that are being reproduced.

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norwaybike
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Joined: 01/26/2007
Posts: 37
I am not aware I could buy

I am not aware I could buy new SUM carbs... Suppliers?
What kind of airfilter do you recommend for use with the SUM carb?

Best regards, Frode

Bigsieuk
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VBMWMO #8791
Joined: 02/27/2012
Posts: 100
Sum

Hi Frode,

There is an original Sum on eBay.de at the moment. A number of suppliers have new manufacture Sum carbs and air filters, RRC tuning, Oldtimergarage etc.

Is the magneto putting out a good spark?

Regards

John

BMWfahrer
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Joined: 05/15/2016
Posts: 11
Hello, you need 1) Sum

Hello, you need

1) Sum Baumuster 769 on carburetor

2) R 11 und R 12 tow carburetor Typ 6/406 SP und 6/407 SP,
Amal Vergaser links und rechts für BMW R 11 oder R 12 (6/406 & 6/407)

3) Bing possible but 2 Carburetor (as a replacement)

Jürgen

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