How to start a B50 :-)

How to start a B50 by Rickard Nebrer

This is what different magazines writes about starting the B50.

Classic Bike Guide: April 1998

"The engine was set up to avoid the B50 Bugbear of Difficult Starting"

The engine was stripped and reassembled, with new electrics replacing most of the original MX's batteryless, points- controlled capacitor system. A tiny 12 volt battery off an electric- start Honda scooter was employed, together with a Boyer Powerbox replacing the old Zener diode, etc (see Chris Read' s explanatory article in CBG No81). Boyer featured again with the I.D. ignition unit, which leaves the points in place but puts hardly any voltage across them; the way this smooths out the ignition was another contribution to easier starting, which Mike demonstrated, despite having flooded it a little, kicking brute into wearing trainers. As part of the quest to make a bike which you could live with, he explained; 'We've retarded the ignition by about 10 degrees - because some duffer might kick it over wrong, and go into orbit if it kicked back.

Classic Bike : August 1984

"Kick-starters are also prone to premature failure, Particularly if no valve lifter is fitted."

" Easy starting was never a B44/B50 strong point."

The Classic MotorCycle : April 1999

Starting the engine is a whole load of fun in itself. Let me begin by saying that since I race a BSA B5OMX I am in a better position than most to appreciate the vagaries of persuading a big Single in to Iife. Even so, the CCM provided a worthwhiIe chalIenge. First of all, fIood the 36mm Amal Concentric then bring the motor to tdc on the compression stroke. Finding tdc is straightforward because the Piston won´t move a millimeter further even when tree or four of your friends jump on down on the kick-start together! Next pull in the valve lifter which depresses the exhaust valve and then gently ease the piston over tdc. You will now have a very slim chance of accelerating the pison fast enough to spin the flywheels with sufficent momentum to carry the piston over it top dead center when it reachescompression again. Heaven help you if you don´t- the CCM punishes carelessness with ruthless efficiency.
What happens if the piston isn´t travelling with sufficent speed is that the spark occurs before the piston reaches the top of the bore. This drives the piston back down the bore at hyper-sonic speed, at the same time returning the kick-start with awe-inspiring force.
If you think a mule has a kick, you ought to try being on the nasty end of a CCM.

British Bike Magazine : October 1990

The B50 is a brute. Its undersized flywheels and 10 to 1 compression ratio combine with the strange lack of a decompressor to make optimum positioning of the piston for kickstarting simply impossible.

Smug "experts" opine that there is a Drill for Starling the B50. Rubbish! Why are they never seen riding B50s? Flood the Amal 930, open the throttle a little, apply about four fifths choken and lunge.

If you are lucky, it will catch; if not, strip off and try again. On about the ninth try, the B50 will probably retaliate. Climbing down from a nearby building, battle is rejoined. An explosion will shake the surrounding buildings and be followed by a series of further explosions - increasingly violent in force - as the throttle is opened to fast idle. Success!

BSA Motor Cycles by Steve Wilson ( Book )

The B50 like the late versions of its great namesake the Gold Star, was a bitch to start. A 10:1 compression ratio made the use of the ( awkwardly positioned ) exhaust-valve lifter a must, and the downdraught Concentric permitted only the lightest tickling before flooding. The continued absence of an air-lever did not help cold starts either.

Two Wheels: December 1972

When the 500 Gold Star was tested several months ago we criticised the poor starting of the bike. The same criticism can be applied to the trial bike. There is no choke fitted and the right amount of flooding has to be guessed.... the result is a first swing start or a long puch to clear the motor. Experienced riders will read between the lines.... The valve lifter routine is a must for the 500, but the 250 can be swung over quite easily on full compression. Disadvantage of the absence of a choke is that before the bike can be ridden confidently it has to be warmed up by blipping the trottle.

Cycle Guide: December 1971

The compression is awesome, and if you don´t know about the compression release and its proper use, you can end up with a hernia or a battered leg, and the machine still isn´t running.

Cycle Ilustrated: April 1973

The BSA is a big fourstroke single, and these beasties take a lot of starting. I am not exactly a novice with such machines, for I have owned and raced a number of other singles, but even so the BSA Proved to be a swine. Kick-starting from cold is just out of the qestion. Being someting of a masochist, I chose the high-compression engine.

Cycle: March 1972.

If you don´t know how to fire up the MX, the bike will bite you.

Cycle World: Jan 1972.

It does require considerable rider weight to drive it through compression and make it fire.

I just say " Good luck " Rickard.

Updated 2000-01-25
© Rickard Nebrér