Boyer mystery

hhh said:

Are you saying you start kicking and then turn on the ignition mid stroke?

Click to expand...

Part of starting a big single is to find compression, then use the decompressor to lose the pressure and move the kickstart to get the piston just over TDC. By turning the ignition off for this bit you do not get a spark at TDC with the risk of a kickback. Plus the Boyer when it sees voltage is primed ready to spark when you use the kickstart in anger for 5 secs before it goes to sleep.

This also works on a Commando, except without the decompression you are left with your foot on the kickstart applying steady pressure as the compression slowly escapes and you finally get to TDC, then you do the proper kick. With the next TDC now 2 revolutions away the kick will impart lots of energy to the flywheel to get it over the next TDC, hence no kickback.

Another way to do this is with the bike off the stand and in gear roll the bike back until you feel pressure, then engage neutral and kick. By rolling backwards you get to TDC from the opposite direction. Good for running starts on the race track as the crank has time to turn before TDC, without this time the rear tyre just slides on the track.

Thanks baz and kommando, after decades of ownership, by now I'm well versed in the big single starting routine, and my leg is tired, I just didn't understand the need for an additional "cut out switch." I just turn on the ignition as the last step with the piston positioned, tickled (depending on the bike, B50 doesn't care oddly), and idle raised 1/2 to 3/4 turn with an extended idle stop screw. The latter was a revelation for one-kick starting. When I first got my B50, I swear I kicked it 300 times before I could even get it to fart until I noticed that it fired when I just barely tensioned the throttle rather than holding it further open. Now I'm going to put in an MX cam and have to learn how to start it all over again. It seems every big single has its own personality and needs.

I contacted Steve Kelly at TriSpark at the time I was considering it and using the advance curve he gave me, and setting the maximum andvance at 28 degrees, the spark timing at under 500 rpm was 8 degrees ATDC.
Dennis

A common error is to route the pick up cables alongside the alternator cables. This can cause no end of issues

Eureka! It was a bad black box.

seattle##gs said:

Eureka! It was a bad black box.

Click to expand...

I wonder if the analog Boyers have electrolytic caps in the trigger circuit that are leaking from age?

I can say my VapeWassell EI never gives kickback on my 74 850...done 20k miles on the ei now.

baz said:

I have an antique power hungry Lucas Rita it's never kicked back in decades
I now have an Alton starter running happily with it

Click to expand...

My mate Tim has a RITA on his Mk2 and it's never missed a beat. Clearly you can't beat quality.

hhh said:

Thanks baz and kommando, after decades of ownership, by now I'm well versed in the big single starting routine, and my leg is tired, I just didn't understand the need for an additional "cut out switch." I just turn on the ignition as the last step with the piston positioned, tickled (depending on the bike, B50 doesn't care oddly), and idle raised 1/2 to 3/4 turn with an extended idle stop screw. The latter was a revelation for one-kick starting. When I first got my B50, I swear I kicked it 300 times before I could even get it to fart until I noticed that it fired when I just barely tensioned the throttle rather than holding it further open. Now I'm going to put in an MX cam and have to learn how to start it all over again. It seems every big single has its own personality and needs.

Click to expand...

An extended idle screw is brilliant on a b50
The starting procedure that I learnt from BSA b50.org is as follows
Take the engine past tdc until you feel the exhaust valve starting to open (you can feel it through the valve lifter lever)
Turn the idle screw in half a turn
Return the kickstart to the top
Tickle the carb
Switch the ignition on and give it a good full kick but don't open the throttle unless it fires and runs first or it will kick back

hhh said:

I wonder if the analog Boyers have electrolytic caps in the trigger circuit that are leaking from age?

Click to expand...

From memory ( have not repaired these since 1988) there is a Tantalum capacitor that can be a problem. The main output transistor is the usual suspect, if the system is operated not connected to the spark plug. Somewhere I have a circuit diagram for this system, silverfish have probably consumed parts of the diagram!!!