This is from the site Bring a Trailer (https://bringatrailer.com/) ...
This 1974 BMW R90/6 was purchased 8 months ago and mechanically refurbished by the seller over a 6 month period. The bike is powered by a 898cc opposed twin with a 5-speed transmission, and work performed by the seller included honing of the cylinders, new seals, and a carburetor rebuild. The brakes, clutch, electrical, and fuel systems were also serviced, and new tires fitted. 20k miles are currently shown, of which the seller has added only a handful. This R90/6 is offered at no reserve with an owner’s manual, factory tool kit, and a clean Ohio title in the seller’s name.
The bike is finished in white with black pinstriping which is believed to be factory applied with only minor touch ups. A previous owner re-covered the seat, while the seller replaced the handlebar grips and exhaust. The master cylinder and front brake caliper were rebuilt, and the fork seals, brake pads, and brake hose replaced. The rear brake shoes were cleaned, and bearings for the steering head and wheels greased. A broken tang on the center stand was repaired, and new swing arm seals installed. Weinmann alloy wheels wear new Metzeler tires.
The control cables were replaced, and the instrument cluster consists of a 140-mph speedometer and a 9k-rpm tachometer. The cluster was disassembled, and the warning lights were replaced with LED items.
Corrosion was discovered on the wiring harness, which was replaced along with the starter, generator brushes, relays, and battery. Norris ignition points were fitted along with Beru wires and Bosch spark plugs.
The air-cooled 898cc opposed twin was factory-rated at 60 horsepower and features dual 32mm Bing carburetors. Power is transferred to the rear wheel via a 5-speed transmission with shaft drive. The transmission is believed to have been rebuilt by the previous owner due to a broken kick-start gear. When purchased, the seller removed the engine to hone the cylinders, and replaced the following:
- Rear main seal
- Neutral switch
- Push rod tube seals
- Base gaskets
- Head gaskets
- Valve cover gaskets
- Silicone oil pan gasket
- Oil pump O-ring
- Mahle air filter
- Braided cloth covered fuel lines
- Petcock screens
- Mahle oil filter
- Driveshaft boot
- Driveshaft bolts
The clutch disc was determined to be good but a new clutch spring plate installed. The valves were adjusted along with the ignition timing, and the drive splines lubricated. The carburetors were also ultrasonically cleaned and rebuilt with kits from BMW before synchronization with mercury tubes.
The under-seat tool tray has a new seal and contains a replacement tool roll with factory tools, an owner’s manual, and a BMW shop towel. The factory tire pump can also be seen attached to the left frame rail. Walk-around, cold start, and tuning videos are provided below.