THE FUEL SYSTEM

The Airhead fuel system is simple in design and straightforward in operation. However, there are several "rubber" parts that come in contact with fuel and therefore don't age well, and then there are several other parts that will simply need inspection. And then, owing to the presence of Ethanol in US fuels, varnish and corrosion can also be an issue. All this means it is impossible to predict all the issues that might be found. We can only offer a list of items to replace, check, and clean thoroughly.

NOTE: For those new to Bing carbs, the units may appear to be identical, but they are NOT. There are numerous parts that will fit either LH or RH carb, but if they are installed in the wrong carb will create problems almost impossible to diagnose. Therefore, we HIGHLY suggest disassembling one carb at a time to preclude the mixing of parts.

Suggested parts to replace:
• All the fuel. Never trust modern fuel over 8 weeks old.
• Both rubber intake hoses
• Both float chamber floats (Bing issued new Ethanol-proof parts)
• Both float needles (Bing issued new Ethanol-proof parts)
• Both float bowl gaskets
• Both low speed jets (The smallest brass jet, typically a #45)
• All O-rings (These are found on all jets and idle mixture screws, as well as pivot shafts)
• All fuel lines (Due to Ethanol, all fuel lines MUST meet SAE J30 spec)

Suggested parts to check:
• Both diaphragms (Bing issued new Ethanol-proof parts)
• Both idle mixture screws (and blow out their passages)
• Both float bowl "enrichening jets" (See note below)
• Fuel tank petcock operation (Fuel valve packings are replaceable.)

Suggested parts to clean:
• Both float bowls (See note below)

► Check the condition of the air filter because it's critical to good carburetion. Additionally, in older models with the air intake above the starter motor, critters often build nests inside the air box and this can be a very hard issue to diagnose.

► Particular attention needs to be paid to the hidden fuel "enrichening jet", because it is almost mandatory for cold starting an Airhead. Looking inside the float bowl, you'll see a round chamber in one corner.

A tiny, nearly invisible orifice at the base connects the large and small chambers. If liquid cannot pass through that orifice, then cold starting becomes nearly impossible. If your Airhead starts on 1 cylinder, then check this orifice on the non-running side.

► It is highly suggested that a "Top Tier" fuel be used that has built-in 'cleaners'. These are necessary to rid the tank and petcocks of built-up scum and varnish left by old fuels. If you wish to use a liquid fuel cleaner, then I can highly suggest a product called StarTron, which is both a fuel stabilizer and cleaner.

Read about it:
https://www.toptiergas.com/
http://www.starbrite.com/startron

THE IGNITION SYSTEM

Always get the motorcycle running with the existing ignition system. Never install a new ignition system until the bike has run at least 100 miles with the existing system.

Points Type Ignitions
► For initial startup only, assume minimal points cleaning is all that is needed. Clean the points where they sit without making any adjustment. A doubled-over piece of 400-600 grit emery will do, then follow that with a piece of paper to blot off any remaining debris. Check the point gap.

► After the bike is running a full service can be carried out... replacement of the auto advance springs, lubrication of the ignition cam face and auto advance mechanism, adjusting the points gap, and finally setting the ignition timing.

BMW Electronic Ignitions
The stock BMW electronic ignition is fairly robust, but there are 2 maintenance steps that should be completed on any new-to-you Airhead.

► Behind the engine's front cover, on the front of the crankshaft, the ignition triggering device is housed in what is called "the bean can". The electrical connection to the "can" is made by a short 6" wire and a 3-position connector. If that connector is white or ivory in color, then it must be replaced. Motorrad Elecktrik can supply a replacement wire/connector assembly which is not listed on their webpage. The complete bean can is removed from the engine, and the new connector assembly added while on the workbench. http://motoelekt.com/

► Poor heat conduction can make the electronic control unit (located under the fuel tank) overheat and burn out. The heat sink compound between the module and the heat sink simply needs to be renewed. On dual-shock models this is located on top of the brake fluid junction. On single-shock models this is located on the RH side, in the electronics area. Separate the 2 parts, clean off the old hardened thermal compound, and replace it with a modern, high grade compound, such as Arctic Silver 5 thermal paste.

Aftermarket EI
Generally, nothing needs to be done with aftermarket electronic ignition systems. They either work or they don't.

Parts to replace
We highly suggest the replacement of several ignition parts common to ALL Airheads because the cost is very low when compared to the amount of frustration they often cause.

Suggested parts to replace:
• Both spark plugs (NGK BP7ES work well in most models.)
• Both spark plug caps (NGK 5000 Ohm ("5KΩ") work great.)
• Both spark plug wires (Wires must be metal core type wires.)

Setting the ignition timing
Due to the changes in gasoline over the last 40 years, it is highly suggested that an strobe lamp be employed when setting the ignition timing. Contrary to the original instructions, the ignition timing should be set at high RPM (4000 to 5000 RPM) using the "F" mark on the flywheel. The flywheel's high speed mark should appear in the timing hole when the ignition ceases to advance any further (aka "full advance"). Accurate ignition timing at "full advance" is ultimately responsible for lowering the combustion temperature and increasing the overall smoothness of the engine at road speeds.

Ignition timing at idle is of little consequence, and pales in comparison to the need for accurate timing on the road.

THE ENGINE

The Airhead engine is extremely robust and asks nothing but use of high octane fuels, regular riding, and have a regular owner maintenance schedule. With moderate care these engines can easily do 250,000 miles between major overhauls.

Valve Adjustment
It is important to note that these engines were designed for "leaded" fuels. Since those fuels are no longer available, valve clearances on most Airheads tend to close up. If the valve clearance ever gets to be zero, not only can damage to the camshaft occur, but the engine will loose compression and run very poorly. Therefore, it is imperative that valve adjustments become a regular part of the owner maintenance schedule. How fast the clearances tighten up varies from machine to machine. Your motorcycle will teach you what it likes. Start with an "every 3000 mile" routine and adjust according to what you find your machine requires.

Therefore, on any Airhead that's new to you, the first order of maintenance is to adjust the valves... then just to make sure, a second time after completing the first 100 miles.

Compression
Compression on an engine coming out of storage will typically be low. In 98% of the cases the compression will rise back to normal levels once the bike is started and ridden. New owners should resist the urge to disassemble the engine until issues persist longer than 500 miles. Compression will continue to rise over the first 5,000 miles, with the bike giving the distinct impression that it is running better with every outing. Remember, improper valve adjustment is the number 1 cause of poor compression.

There may well be oil leaks and other issues, but if possible it is much wiser to delay repair until the following winter. Then, after thousands of miles, all the issues will be fully understood, and can be corrected during a single repair.

Push rod tube seals
At the base of each chrome push rod tube (PRT) is a black, rubber seal. These make an effective oil seal by applying a slight pressure between the PRT and the engine case. After many years the combined effect of oil, fuel, UV, and engine heat will cause these 4 seals to harden and then they begin to weep oil. The only fix is PRT seal replacement, which requires a top end disassembly.

On about 95% of the bikes taken out of storage these seals will show some degree of oil leakage. However, due to the cost of BMW parts, we suggest that it is more important to place mileage on the engine and determine the viability of all the top end parts so that a full top end repair can be completed during a single disassembly. In other words, for the first several thousand miles it's far less expensive to simply keep a watchful eye on the engine oil level.

LUBRICATION & FILTERS

Proper lubrication is important on an Airhead. However, due to advances in lubrication and mandates by the US EPA, lubrication oils have changed significantly since your Airhead was new. Oil weights and types that were once common are now considered "specialty oils" and may require research to locate. This is especially true of engine oils.

The Engine
Without going into details (which are covered extensively elsewhere), your Airhead engine requires an API rated oil of SF, SG, SH or any combination. Modern car oils API rated SM and SN will not adequately lubricate the Airhead engine. Sectro, Valvoline, Castrol and others still make this type oil, but it will generally not be found at mass markets like Walmart. In most areas of the country and during most weather conditions you'll want to use 20/50 or 20W50 weight oil in the engine. (I found Valvoline 20W50 VR1 "racing oil" at my local auto parts dealer with the correct API specs.) Mobil-1 15W50 is also a viable candidate.

NOTE: Before changing the engine oil filter read and understand the information at the bottom of this page.

Gearbox, driveshaft and final drive
These 3 oil reservoirs can benefit from advances in gear oil lubrication. While your original manual may suggest 90W gear lube, most gear lubes these days are multi-grade oils, such as 75/140, in either regular mineral based or full synthetic. Experiment and see what your machine likes. Most new gear oils far exceed the original BMW requirements.

Front forks (shocks)
No other oil is as important to good handling (and therefore your safety) or as over-looked as the front fork oil. Clean and equal amounts of fork oil help keep the bike going where you intend. Generally, any high grade of "fork oil" between 7 weight and 10 will work. And the oil weight can be varied within that range to obtain the ride characteristics you desire.

Rear shock(s)
The OEM rear shock(s) are sealed units and cannot be serviced. The maximum life of the rear shock(s) is 5-7 years. A good, economical replacement shock is made by Hagon. The correct shock is 340mm center-to-center.

Swing arm
The swing arm bearings are lubricated independently from each side. Access is gained by popping off the plastic cover caps. A special "needle nozzle" is required to get the grease onto the bearings. Injecting new grease is an important part of pushing out water and dirt from the swing arm bearings.

Wheel bearings
At some point you will want to make sure the wheel bearings are properly lubricated. Wheel bearing maintenance isn't needed very often, but when overlooked can result in dangerous handling. So it's best to check and be safe.

Head post bearings
The forks turn on tapered roller bearings which need their lubricant replaced every 10 years or so. It is common to feel a grittiness or "hunting" within the steering bearings due to the presence of old, oxidized grease. If there is no rust on the bearings, then the old, solidified grease simply needs to be washed out and renewed. This can be done by dropping the front forks 6" and washing the bearings in place.

Proper steering directly depends upon the fork bearings having zero resistance to turning, while at the same time having zero "free play" in the bearings. It's a delicate adjustment that requires some pre-loading of the head post bearings and the proper water-resistant grease. Consult your shop manual.

Engine oil filter
There are several things you need to understand before attempting to change the Airhead engine oil filter. The 2 main ones are:
► Airhead engine oil filters take at least 3 different physical forms. They are not interchangeable, but to the untrained eye they can look nearly identical. You must use the filter that is correct for your model or engine damage can result. The biggest difference is that engines with an oil cooler use a different filter from the non-cooler models.

► Secondly, for /6 and later machines the fitting of the white o-ring is critical to engine lubrication. This o-ring has been called the "$2000 o-ring" and it's proper fitting should be thoroughly researched BEFORE attempting to change the engine oil filter. If you are not sure of how this o-ring fit is properly measured and installed, then it is much safer NOT to change the oil filter until you do understand it.

Read about it:
https://www.airheads.org/airlore/techtips-main/tt-11-engine/178-oilfilter-change-procedures-a-technical-info-rev-by-author-12-07-2007

WHEELS & BRAKES

Wheels, tires and brakes are items which need a thorough safety check before you hit the road on your new-to-you Airhead.

Tires
Due to their multiple failure modes, tires older than 5 years generally shouldn't be trusted. Since the mid-1970's tires sold in the US have a molded-in date code, which typically consists of 4 digits. This code typically appears on only one sidewall. 

There are many great tires available for these vintage rim sizes. The least expensive, most basic tire I advise using on Airheads is the Bridgestone S11 Spitfire. There are also great European tires from Michelin, Continental, Metzler, and Heidenaur.

► It is also good to note that modern tires need about 6psi higher inflation than the pressures listed in most of the original owners and shop manuals. I'm running 35psi front, and 31psi rear on an R100 RS.

Inner tubes
If you replace an old tire, then replace the old inner tube. Inner tubes with patches should always be replaced. Inner tubes move inside the tire during use, so a light coating of talc can act as a "lubricant".

Mechanical drum brakes
These brakes typically collect a minor coating of rust, which makes them extra "grabby". No disassembly is generally needed, just apply them over and over within the first several miles of riding to knock off the rust and bring them back to life. Some minor adjustment may be required since the rust accelerates wear during that period.

Hydraulic disc brakes
Hydraulic disc brakes do not age well and can require quite extensive work to restore them to a safe working condition. For your safety, full attention should be given to the complete hydraulic system before the bike is ridden.

• Due to water absorption, BMW advises annual brake fluid replacement. The useful life of DOT4 brake fluid in a motorcycle is very short. Therefore you'll need to do a complete brake fluid flush and replacement before any riding. On a /6 or /7 bike with the brake master cylinder under the fuel tank, this action can be labor intensive.

NOTE: DOT4 brake fluid is highly corrosive and will eat the paint off any surface it remains on. It is always best to end every hydraulic brake repair session with a gentle washing using hot, soapy water. This paint damage is especially true of fuel tanks, fairings, and frames.

• OEM flexible brake hoses are known to regularly fail internally, without warning and with no visible clues. This is a complex issue and has its own repair article HERE.

• Brake pads have evolved significantly in the last 20 years. It is highly advisable to replace any older pads with modern brake pads from EBC. Again, improved braking is a good thing.

Wheel bearings
Lubrication of the wheel bearings is covered under Lubrication.

Read about it:
https://spieglerusa.com/
https://ebcbrakes.com/motorcycle-products/

ELECTRICAL

The OEM electrical system is a very good product, and even after decades very few items will have failed. However, it is important to note that back in the day Airheads were the kings of the road and these bikes amassed unheard of mileage in all types of weather. 40 years later, it is best to assume that prolonged exposure to water may have left some of the connections in an "iffy" or intermittent state due to formation of microscopic corrosion. There are also the Airhead quirks you want to learn about before you break down 300 miles from home. Here's some tips on the top items to check.

Owner modifications
Back in the day numerous electrical system modifications were commonly suggested to "improve the reliability". One of the common ones for the RT and RS was to move the fuses from the headlamp back to the seat area. 40 years later, the lower quality of these home remedies can end up causing electrical problems. When electrical issues arise, always view "home wiring" (if present) as the primary suspect.

Alternator
Other than needing new brushes every 80,000 miles, the charging system is very reliable. Those who get into trouble have generally added too many electrical accessories. Still there is one quirk you need to know to be a successful Airhead rider... When you turn the ignition key ON, always check to insure the charge light in the gauge cluster lights up. If that incandescent bulb ever burns out, then the charging system will not operate.

Fuses
• Single rear shock models... fuses are usually located in a small black box hidden above the LH side cover
• Dual rear shock models... fuses are usually located inside the headlamp shell
On most Airheads there are 2 fuses, both 8A rated, and both of the older German pointy-end style. These 2 fuses are a source of recurring trouble since they depend upon spring pressure applied by clean contacts in order to pass current. It is best to scrap the older white porcelain fuse in favor of the modern glass tube replacements. Or better yet, replace all fuse holders so that modern 10A ATM "flat pack" automotive fuses can be used. If you insist on using the older German style fuses, then you must carry your own spares.

► Most Airheads do not have a "main" system fuse, meaning... 1) not every electrical device is fuse protected (thus it is possible to burn up an expensive harness if you are not careful). And 2) if electrical accessories (grip heaters, cell phone outlets, etc) are added, then each accessory requires the mandatory addition of its own fuse.

Voltage regulator
The OEM voltage regulator was very reliable for its day, but it's a mechanical type regulator with multiple moving parts. Now, 40+ years later most are completely used up. A modern, transistorized version (with zero moving parts) is HIGHLY recommended. Additionally, many owners are opting for the newer sealed AGM and lithium batteries which require a slightly higher charge voltage. This is only possible with a modern regulator. If you experience charging issues, then the modern solid state regulators are the best replacement. These are available from third party Airhead suppliers.

Battery cables
Electric starter motors rely upon perfect electrical connections at both ends of both battery cables in order to be reliable. If you replace your battery, then take the time to check your battery cables.
• Negative (-) side battery cables have issues making good contact at the gearbox end. The attachment fastener is generally the hollow gearbox breather bolt which can only accept very limited torque. In order to make good contact, more fastener tightening is not an option and will not substitute for clean terminals.
• Over time, Positive (+) battery cables can wick battery acid inside the jacket and through the braid, all the way to the starter motor. If blue-green corrosion is observed at the starter motor terminal, then the positive battery cable must be replaced.

Bulbs
Replacing the OEM incandescent light bulbs over time with modern LED replacements can have multiple benefits for the Airhead owner. LED bulbs are generally much brighter, making the motorcycle more visible to other drivers (thereby increasing rider safety), and consume much less electrical power (thereby making more power available for other electrical accessories).

Also, LED bulbs are available in colors. Using red LEDs in the tail lamp and a blue LED in the Hi-beam indicator can further increase the bulb's visibility. Using softer blue or green LEDs for gauge illumination can reduce nighttime glare from the gauge set, while at the same time making the gauges easier to see.

► Airhead bulb suggestions....
• The biggest boost you can give your electrical system is to install an LED headlamp bulb. However, new bulbs are coming on the market everyday. You want an H4 style LED headlamp bulb, 5000 to 6000K, with a light output of at least 2500 Lumen. At 25W these uses less than half the power of the OEM bulb while being about 3 times brighter. The center post of the bulb should be 3-sided to achieve the best light pattern for motorcycles. Most of the available bulbs are flat, 2-sided, so you'll need to search.

.

• Super Bright LEDs ( https://www.superbrightleds.com) is a great source for general vehicle replacement bulbs, including the smaller bulbs found in the Airhead gauge cluster. However, I do not recommend their headlamp bulbs.
• Remember: the alternator warning lamp in the gauge cluster must remain an incandescent bulb in order for the alternator to work.

Intermittent connections
Due to 40 years of riding in the rain, intermittent electrical connections are found on about half of all Airheads. Water promotes corrosion on the bronze electrical connectors and electrical connectivity suffers. If you have this issue, then I highly suggest the use of a product called NO-OX-ID by Sanchem. Available on Amazon, this professional electrician's paste prevents water intrusion, reverses electrical contact corrosion (oxidation), and dramatically improves electrical connections. You'll only need to apply a tiny amount (1/2 drop) to each contact, meaning the smallest package (7ml) is enough for ~10 motorcycles. I use it on both ends of both battery cables, fuse ends, relay plugs, all harness connectors, low wattage light bulbs, inside the ignition switch, horn terminals, the gauge pod connector, all the contacts inside the headlamp shell... everywhere. In order to apply the paste, you'll need to unplug each connector, one at a time, and coat the male contact. It's a tedious but necessary task, that can be spread over several weeks.