B25 trials project.

Here you can publish Your projects bikes.
Only BSA singles

Moderator: minetymenace

FranktheWelder
>100
>100
Posts: 106
Joined: Tue Dec 10, 2019 1:35 am
Location: Bellows Falls Vermont
Contact:

Re: B25 trials project.

Post by FranktheWelder »

beat wrote: Wed Jan 13, 2021 8:08 pm hi JB

yes, shorter stroke = less advancing.

but basically : there is a horrible mistake done by BSA , - covering maybe all models.
and this mistake is keeping still alive in all brains of BSA owners :

Kickstarting the engine by a ignition timing, set to some degrees still before TDC.

this is totally wrong :!: :!: :!:

for the kickstarting process, ( same as the electric starting process ) - the timing must be set to somewhat of two to four degrees AFTER TDC. :!: :!:

and this is very easily to modify on the Alu.

I have done it on two engines, B50 and a Gold Star and great benefit. -- NO MORE EVER A KICKBACK !

and when you make this experience , the energy you set in to the leg to kick it over is definitely stronger.

so, IMO, a electronic Ignition where the advancing curve is ending by 32° ( Road ) ore 34° ( Racing ) for a B50 is a bad thing.
guess for a B25 it should be 13° ore 14° ATU, - makes 26° ore 28° Flywheel.

beat
Not sure I understand but ATU is the total advance available? and ALU is the ignition module?
machines, materials and motorcycles.
User avatar
minetymenace
Gerry1
Gerry1
Posts: 7783
Joined: Wed May 26, 2004 1:00 am
Location: On the edge of Salisbury Plain, England
Contact:

Re: B25 trials project.

Post by minetymenace »

Frank, beat has few faults; a propensity for metric threads being his greatest sin, and of the many languages he speaks (and writes) his English is the most hilarious. I think he means the automatic advance and retard unit in all cases here (for ALU read ATU).

Beat extends the slots in the unit to give the unit the ability to advance more than standard (16-17 degrees on the cam), this means that when the engine is at full chat, the fully advanced is as standard, but at kickover speeds (full retard) the ignition occurs after TDC hence easier starting with no kickback, details here......re-reading this I'm not sure my English is any better than beats, but I hope you understand.
There is no evidence to support the notion that life is serious.
Abyssinian Wire-Haired Tripehounds Gnash.
beat
>1400
>1400
Posts: 5826
Joined: Sun Jun 04, 2006 5:33 pm
Location: Switzerland

Re: B25 trials project.

Post by beat »

minetymenace wrote: Thu Jan 14, 2021 9:35 am (for ALU read ATU).
<209 <906 <944 <058
Velofello
1-10
1-10
Posts: 8
Joined: Wed Apr 17, 2019 10:42 pm
Location: New Jersey

Re: B25 trials project.

Post by Velofello »

I find this interesting. My experience has been that setting the retarded ignition value at atdc means the bike won't start on the kick starter, or if it does, it is with difficulty. If it does start, it runs pretty nice though. Had this with my B44 and a little Gilera.

Ed
FranktheWelder
>100
>100
Posts: 106
Joined: Tue Dec 10, 2019 1:35 am
Location: Bellows Falls Vermont
Contact:

Re: B25 trials project.

Post by FranktheWelder »

Let me see if I get this.
1) bike is easy to start if firing slightly after TDC,
2) Beat is saying 27* advance is good but stock is much less so he mods stock advance system <216 <216
3) Electrex has 28 degrees advance (retard) so I should start with static time something after TDC.
4) Where can I buy a bag of lock washers cheap? <215
machines, materials and motorcycles.
User avatar
minetymenace
Gerry1
Gerry1
Posts: 7783
Joined: Wed May 26, 2004 1:00 am
Location: On the edge of Salisbury Plain, England
Contact:

Re: B25 trials project.

Post by minetymenace »

You got it Frank, but beat is talking about B50s, he only briefly mentions B25s. I have never found a problem starting my B25 with stock points and ATU. Now, as you will hopefully spend longer with the ignition fully advanced than fully retarded, the fully advanced position is what you need to get right in the end, and this will only be done when the engine is warm using your fuel of choice, and the fully retarded setting will be whatever it will be when the ignition is finally set. If your carboration is set correctly, it will start if the ignition is +/- 10 degrees of where it should be and you can very quickly dial it in.

So set it the best you can and move on, near enough is good enough at this stage in the build (and welding porn is far more interesting than labouring over the minutiae of ignition timing).

P.S. Not sure about your lock washers, we only have lock keepers in this country, it seems that all the rain keeps the locks pretty clean. >44
There is no evidence to support the notion that life is serious.
Abyssinian Wire-Haired Tripehounds Gnash.
Post Reply