Starting & Starter Problems

Functioning,starter circuits & associated parts:

The starter motor is a powerful electrically operated motor. The starter motor may have to provide upwards of 1/2 to 1 horsepower.  In cold weather more power from the starter motor will required. The starter motors in our Airheads, like all vehicle starters, are not very efficient motors. The Valeo is more efficient than the Bosch.  Quite a lot of amperes might be needed under some rather common conditions. Starter motors are, at best, 60% efficient due to magnetic field losses, friction losses, etc.

745.7 watts is DEFINED as ONE horsepower. If the system is a nominal 12 volts during cranking (typical, with good battery, wires, and connections, voltage as read at the starter terminals), then 745.7 divided by 12 equals 62 amperes. Due to the efficiency losses, & the need for many more amperes to BEGIN engine rotation, it is NOT uncommon to require twice that number of amperes. The power rating of the most powerful of the three Bosch units used on the Airheads was 0.7 KW. 0.7Kw is 700 watts; divided by 12 volts is 58 amperes. Notice that the starter is also rated at 320 amperes. That is the supposed maximum drain under a severe load. That is equivalent to 3,840 watts….and is equivalent to a bit over FIVE horsepower. The battery, cold day, thick oil, so-so starter, ETC., may need to provide a LOT of power! If the battery is marginal, it may not have enough power to cause the starter motor to rotate the engine properly for starting ….possibly not rotate it at all.

There must be a means of switching on and off the large amount of electrical current to the starter. A heavy-duty solenoid-operated switch is physically located on the starter motor itself. It is a fairly large round cylinder with two electric terminals of the bolt/threads type and one small spade type which supplies a modest amount of electricity to the solenoid from the starter relay, located along the backbone of the motorcycle.   

You must be a member to view complete articles on this website. If you are already a member, you can log in here. If you aren’t a member yet, you can purchase a membership here.

Continue readingMore Tag

Starting your Airhead motorcycle, including in cold weather

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.  

You must be a member to view complete articles on this website. If you are already a member, you can log in here. If you aren’t a member yet, you can purchase a membership here.

Continue readingMore Tag
Scroll to top