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  • Writer's pictureKai

BMW K100 Carburettor Overhauling

How do you eat an elephant? Bit by bit. These carbs are really taking a lot of time to overhaul.

Before we start disassembling the complete rail its beneficial a) taking detailed shots and b) maybe a video on the whole mechanics so you have a reference for yourself at hand when it comes to assembly.

Here´s why. First, be aware there´s no official manual available from BMW. No spring plan, nothing. Also, you will not get any spare parts other than buying a second (used) pair.

I´ve prepared 4 numbered plastic bags for each carb. Taking a structured approach during disassembly turned out being absolutely helpful.

Also there´s different kinds of metal used (steel, brass and aluminium) so polishing the different part takes different tools.

To get rid of the first coarse dirt it is recommended to put all metal parts in a petrol bath first. After that, use either a nylon, steel or brass whirewheel to polish. Or one after another, depending on the material.

Be careful with the aluminum rails. You shouldn´t use a highly abrasive wheels rather than 1200 wet sand paper. I found that works best. The finish can be done with Autosol polish and a cotton wheels hard / soft. Here´s the whole set.

The two screws holding the throttles are press fitted. I recommend using a non worn screwdriver with thight pressure getting these out. Vice verca, use Locktite during assembly for a good piece of mind.

Another tip. Putting in the throttles during assembly, most throttles have a "10" stamped. Watch out the correct direction when putting them in from the upper side, not the down.

Put the already re-assembled carbs on only one rail first and don´t tighten the screws too heavy! Then add the second rail.

The last piece to add is the mount holding the injection regulator. This will finally center the carbs on the rails. After this you´re good closing all screws in the rail itself holding the carbs.

Another tip. It´s maybe worth painting all steel as they will defintely start to rust after time. I´ll do this at a later stage as it requires using petrol restant 2K lacquer.

And this is where I started....

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