Forum bmwbike.com

...i'm afraid that i need some motorcycle help!
I'm having big trouble with my Sum carburetor on the R11 (series 3-the same as on the R12). It's so worn out that it fouls the spark plugs in only two days! the plugs are black with carbon and soot.
is it possible to rebuild them so that it works like new? and do you know who can do it?
or should i be looking for a reproduction-if they actually work.

if you've got any ideas, i'd be glad to hear them.

-barry

Hey,
what's about changing the temperatur-range of the plugs (if the engine works well, either)

tried it...the plugs are the hottest i can get, but it still runs too rich-nothing much happens when i turn the mixture screw in or out.
i assume that i need a new needle and seat. but what to use as a retrofit and and how to get it done, i've no idea.

I have this problem with other kindo of carbs, amla and bings, and are many "variables", like the gas for example.
May be is it important to reduce the jets, and then, the needles.
May be reducing the jets would be rigth.
Simply change the existing jets by one mesure in less.
It has been rigth in my old bikes, going from 045 to 035.

You might try posting this to the Yahoo Kradrider Group.

http://uk.groups.yahoo.com/group/KRADRI ... d=25164877


There are a lot of R12 guys there. I am sure you are not alone with your problem.

Best regards,

Bruce

hi barry,
i personnaly run a lot with mine (10.000 per year) which is equiped with the original sum carburator. i use BOSCH W7AC plug wich are very good, no problem to declare !
By the way, it is normal to get the plug dark as those machine need more fuel than the other to cool as cylinder are in cast iron and are lateral engine. I need an average of 10lt fuel per 100km with an heavy military side car for info.
If u need more don' hesitate to contact
regards,