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1973 BMW R 90/6 Overview
BMW R 90/6 is an all-round motorcycle, displacing 898 cc. Power comes from a Four stroke, two cylinder horizontally opposed Boxer, pushrod operated 2 valves per cylinder engine, a compression ratio of 9.0:1. On the performance side, it delivers 44.1 kW @ 6500 rpm of peak power and 73 Nm @ 5500 rpm of torque. On the road, the 1973 R 90/6 tips the scales at 210 kg, carries an 18-litre fuel tank, offers a seat height of 810 mm and spans a 1465 mm wheelbase. That's roughly 21 kg heavier than the average all-round motorcycle in our database. The full 1973 BMW R 90/6 spec sheet below covers every technical detail, from suspension travel to tyre sizes.
1973 BMW R 90/6 compared with other bikes in the All-Round category
We checked the recorded figures for the 1973 BMW R 90/6 against up to 497 bikes in the All-Round category in our database, counting each model once at the model year nearest to this one.
- Only 31 of the other 145 bikes in the All-Round category have a higher power output than the 44.1 kW of the R 90/6.
- With 898 cc, the R 90/6 has the joint 109th largest engine displacement of 497 bikes in the All-Round category, 53% above the category average of 588 cc.
- Power-to-weight ratio of 210 W/kg is higher than that of 104 of the other 135 bikes in the All-Round category.
- Narrowing the field to the 23 models within five model years of it, the power output of 44.1 kW is higher than that of 15 of the other 22.
1973 R 90/6 - Pros & Cons
Strengths
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Strong power output: With 44.1 kW @ 6500 rpm and 73 Nm @ 5500 rpm of torque on tap, the R 90/6 is no slouch for its class.
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Strong front braking: Stopping power up front is strong thanks to the disc setup, with plenty of room to upgrade further with braided lines.
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Large fuel range: An 18-litre tank means fewer stops on longer rides - a genuine plus for touring or a lengthy daily commute.
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Low-maintenance final drive: Running a shaft final drive cuts out the regular chain cleaning and tensioning that most bikes need.
Considerations
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Carburetor fuelling: Expect to spend more time keeping the carbs in tune, especially after long storage periods or a change in altitude.
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Drum rear brake: Rear braking comes from a drum, not a disc - it does the job but won't match the feel or fade resistance of newer equivalents.
Wear Points & Servicing Notes
Heat management in traffic
Because the R 90/6 relies on airflow rather than a coolant jacket, expect noticeably more radiant heat at low speed and in traffic. It's inherent to air cooling, and ventilated gear largely offsets it.
Carburetor maintenance
Carburetors on the R 90/6 need periodic attention - pilot jets and float needles are the first parts to gum up after the bike sits, and the first thing to check if idle or throttle response degrades.
Brake disc and pad wear
Braking up front comes from single ∅260mm disc, 1 piston caliper - solid stopping power, with disc and pad wear best checked on the same schedule as tyre changes.
Suspension condition on used examples
The R 90/6's suspension runs Telescopic hydraulic forks at the front. The rear uses Long swinging arm with adjustable strut. Fork-seal condition and rear linkage play are the two things worth checking before buying used.
Final drive maintenance
The R 90/6 uses shaft final drive: essentially maintenance-free day to day, with periodic gear-oil changes the only real service item.
Frame & chassis check
Built around a Double loop tubular frame with bolt on rear section, the R 90/6's chassis is straightforward to inspect: look for corrosion, cracks or repair welds around stress points like the head-stock and swingarm mounts.
R 90/6 - Buying & Maintenance Guide
What to check before buying
Before handing over money for a used 1973 BMW R 90/6 with its 898 cc all-round, cover the fundamentals: service book and oil change history, drivetrain wear, and any sign of oil weeping around the casings. This model runs shaft final drive, so ask for proof the shaft-drive gear oil has been changed on schedule - it's easy to overlook since there's no chain to draw attention to it. Now 53 years old, this all-round is as likely to show age-related wear (perished rubber, seized fasteners, degraded seals) as mileage-related wear. Cold-starting it yourself tells you a lot - a healthy R 90/6 should catch quickly and settle into a smooth idle.
Oil and filter changes
Nothing protects the R 90/6's 898 cc four stroke, two cylinder horizontally opposed boxer, pushrod operated 2 valves per cylinder. like disciplined oil changes - stay on the manufacturer's schedule (roughly every 6,000 km or annually). The sump holds 2.5 l, so budget for that volume of quality motorcycle-specific engine oil. With a 9.0:1 compression ratio, running the octane grade specified in the manual matters more than on a lower-compression engine. Match the viscosity grade to what the owner's manual specifies, not what's cheapest.
Carburetor upkeep
Deposits in the carbs are the usual culprit behind poor running on a stored R 90/6 - strip and clean the float bowls before the first start. Pilot jets clog first and get overlooked most, so make a point of checking them.
1973 BMW R 90/6 - Frequently Asked Questions
What engine does the 1973 BMW R 90/6 have?
The 1973 BMW R 90/6 uses a Four stroke, two cylinder horizontally opposed Boxer, pushrod operated 2 valves per cylinder. engine with 898 cc of displacement. It is air cooled.
How much does the 1973 BMW R 90/6 weigh?
The 1973 BMW R 90/6 weighs 210 kg. This is the manufacturer's wet figure.
How much power does the 1973 BMW R 90/6 make?
The 1973 BMW R 90/6 produces 44.1 kW @ 6500 rpm of power and 73 Nm @ 5500 rpm of torque. These are peak figures.
What is the fuel tank capacity of the 1973 BMW R 90/6?
The 1973 BMW R 90/6 has an 18-litre fuel tank. At around 5-6 litres per 100 km, that is roughly 300-360 km between stops.
Is the 1973 BMW R 90/6 suitable for shorter riders?
The 1973 BMW R 90/6 has a seat height of 810 mm. This is a moderate seat height that suits a wide range of rider heights.
What brakes does the 1973 BMW R 90/6 have?
The 1973 BMW R 90/6 uses single ∅260mm disc, 1 piston caliper at the front and 200mm Drum at the rear.
What tyre sizes does the 1973 BMW R 90/6 use?
The 1973 BMW R 90/6 runs 3.25 - H19 front and 4 - H18 rear tyres. A good selection of sport, touring and all-weather rubber is available in these sizes.
What gearbox does the 1973 BMW R 90/6 have?
The 1973 BMW R 90/6 is fitted with a 5 Speed transmission.
How much oil does the 1973 BMW R 90/6 take?
The 1973 BMW R 90/6 takes 2.5 l of engine oil at a full oil and filter change. Always verify against the dipstick or sight glass after filling.
Key Specifications
Engine
Four stroke, two cylinder horizontally opposed Boxer, pushrod operated 2 valves per cylinder.
Power
44.1 kW / 60 hp @ 6500 rpm
Torque
73 Nm / 7.44 kgf-m / 53 ft lb @ 5500 rpm
Fuel Capacity
18 Liters / 4.75 US gal
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Full 1973 BMW R 90/6 Specifications
Year
1973 - 76
Make
BMW
Model
R 90/6
Make Model
BMW R 90/6
Seat Height
810 mm / 31.9 in
Wheelbase
1465 mm / 57.67 in
Height
1080 mm / 42.5 in
Length
2180 mm / 85.82 in
Width
740 mm / 29.13 in
Oil Capacity (l)
2.5 l
Oil Capacity (Quarts)
2.6 Quarts
Fuel Capacity
18 Liters / 4.75 US gal
Wet Weight
210 kg / 462 lbs
Stroke
70.6 mm
Displacement
898 cc / 54.8 cu in.
Engine Detail
Four stroke, two cylinder horizontally opposed Boxer, pushrod operated 2 valves per cylinder.
Bore x Stroke
90 x 70.6 mm
Compression Ratio
9.0:1
Cooling System
Air cooled
Fuel Induction
2 x Bing constant depression carburetors
Ignition
Battery ignition
Lubrication
Gear driven pump
Spark Plug
Bosch W 200 T 30 / Beru 200/14/3 A / Champion N7Y
Starter
Electric
Chain Size
Shaft
Clutch
Dry single plate, with diaphragm spring
Final Drive
Shaft
Gear Ratios
1st 4.40 / 2nd 2.86 / 3rd 2.07 / 4th 1.67 / 5th 1.50:1
Transmission / Drive
5 Speed
Fork Tube Size (mm)
36 mm
Fork Tube Size (in.)
1.42 in.
Frame Type
Double loop tubular frame with bolt on rear section
Suspension - Front
Telescopic hydraulic forks.
Suspension - Rear
Long swinging arm with adjustable strut.
Wheel Travel - Front
208 mm / 8.1 in
Wheel Travel - Rear
125 mm / 4.9 in
Charging System
12V 280W alternator
Brakes - Front
Single ∅260mm disc, 1 piston caliper
Brakes - Front
Single Ø260mm disc, 1 piston caliper
Brakes - Rear
200mm Drum
Tyres - Front
3.25 - H19
Tyres - Rear
4.00 - H18
Wheel Ratio - Rear
1:3.09 or 1:3.2
Wheels - Front
1.85 - B19
Wheels - Rear
2.15 - B18
Specifications are compiled from manufacturer documentation and cross-referenced
technical sources, and corrected on an ongoing basis.
Spot an error? Let us know.
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