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Starting Your Airhead Motorcycle in Cold Weather
© Copyright, 2002, 2003, 2007, 2013, 2017, 2018. R. Fleischer
|It was in November of 1971 that BMW first, and almost lastly, recommended opening the throttle some during cold starts. This can be a necessity depending on the bike, the temperature (does not have to be really quite cold), & how the carburetors and cables are adjusted. That is still true for later Airhead models, but BMW dropped the recommendation of slightly opening the throttle. Too bad, because that may be necessary or quite helpful. For many Airheads, a bit of throttle playing is helpful even in mild weather startups (seldom if the engine was still warm or hot).|
Cold weather starting is nearly always done, & properly so, by using 100% full choke and manipulating the throttle a bit during cranking, as the engine begins to start. Have the clutch lever at the handlebars pulled-in during the cranking to reduce loading of the starter motor by the transmission with its cold thick oil. Helps the battery too.
Many manuals, including the factory Owners Manuals will say to not touch the throttle. In my experience, that is wrong. I have found that most Airheads require some throttle manipulation upon starting in cold weather, and often in mild weather.
As soon as the engine is running, reduce the amount of choke as soon as you can, yet if you need to, and you likely will, keep 'some' choke on, until you have smooth running, including when riding. Too quick a reduction may result in the engine dying and needing a restart. Typically the choke lever is returned to ~half-way within half a minute. Even in the coldest weather, the choke lever should be returnable within a few minutes to the half-way position, and not long after to full off ...or, nearly so. For very cold weather, try to keep the rpm between 1200-1500 during non-moving time until some decent warmup is had.
Never blip the throttle to high rpm when starting, this is particularly very bad with a cold engine and wear will be high. In some situations you can break rings or collapse an oil filter with a quite cold engine. Generally, you can start an engine & take off modestly, using quite moderate rpm, after 30 seconds to 2 minutes of high idle rpm (1200-1500), if the temperature is down to as low as 40°F or so. I suggest using modest throttle when taking off, and not going over 4500 rpm, preferably not over 4000, until the engine is warmed some, which takes a couple of minutes.
Warm the engine a bit longer the colder it is. An engine at 0°F may seem to require 5-10 minutes of warm-up, but you can start the engine, let it run for a minute or two, then take off gently, using light throttle & quite moderate RPM, until the engine is warmed. Be cautious when first moving off, if the temperature is fairly cold 40 and more so the colder it is ....because not only is the engine affected, but so is the transmission and rear drive, even such as wheel bearings, etc. Taking off in quite cold weather can result in oil spewing out the top oil breather/inlet of the rear drive ....worse if speed is increased too soon before the rear drive warms up. Remember that wear increases the cold the mechanicals at startup.
If consistently starting in cold weather, you should change to a Winter grade of oil, & the grade to select is in a chart in your owners booklet, but I have the very latest BMW chart in my website, about half-way down this article:
For Airheads with the choke lever mounted on the air-cleaner clam-shells (pre-1981), the lever is down for choke on, & the lever points to the rear for choke off. Some Clymer's manuals are wrong, and have that backwards!
When the engine is bitterly cold it is best to warm the engine before starting. It is better to have the entire motorcycle above freezing; in, say, a heated garage. Wear on the engine, transmission, rear drive ...and other parts ...is vastly increased during extreme cold-starting. But, warming the motorcycle is hardly always practical.