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Bsa wm20 - 1941


jerichoe1961

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I hope that somebody can help me with my BSA WM20 that I have just acquired.

 

I am confused as to the advance/retard lever. Contrary to what I have been told by other people, if I am sat on the bike it appears to be fully advanced when the lever is pushed away and then retarded when I pull it towards me for starting. When started it seems to run fine when I push it away again but it would be racing if pulled towards me.

 

I hope that this makes sense and any help would be greatly appreciated.:-D

 

 

jerichoe1961photo 1.JPG

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It depends on which assembly is fitted. Does the A/R cable enter close to the cylinder or close to the battery ?

 

As standard it would have had a 'tight wire' advance but the post-war fashion was for 'slack wire' advance which does have the advantage that the bike can still be ridden if the cable breaks.

 

However, retarding the ignition usually lowers the rpm, so if the revs are increasing as you pull the lever back, that would suggest that you are indeed advancing it and that you have the conventional set-up.

 

If you remove the points cover, it's quite easy to see which way the assembly is moving.

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By zooming in on your picture, I'm sure I can see that your mag cable enters at the rear of the mag near the battery. In which case you have a correct tight wire advance. So advance by pulling the lever towards you. Always assuming that you have the correct type lever, and not the type fitted to Ariel W/NG's. The points on an M20 will rotate clockwise.

I'm just confirming what Rik says. Ron

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By zooming in on your picture, I'm sure I can see that your mag cable enters at the rear of the mag near the battery. In which case you have a correct tight wire advance. So advance by pulling the lever towards you. Always assuming that you have the correct type lever, and not the type fitted to Ariel W/NG's. The points on an M20 will rotate clockwise.

I'm just confirming what Rik says. Ron

 

Hi, thanks for your reply. You are correct that the cable enters at the rear of the mag. I just took the cover off the points and when I pull the lever towards me the cable goes tight and the plate behind the points turns anti-clockwise. Hope this makes sense.

 

thanks again

 

andy

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Thanks to everybody for your help. I now understand the advance/retard lever :laugh:

 

Two things:

 

1. What does the throttle stop screw actually do. I get the idle screw but not the throttle stop??

2. Anybody know where I can get either an original front number plate or a good repro?

 

Thanks again

 

Andy

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The throttle stop screw is just that. The further you screw it in the further it stops the throttle slide from descending and increases your tick-over speed.

 

I think you'll find that by the year of manufacture of your bike, number plates were deleted. The number plates as fitted to the earlier deluxe models require a totally different front guard with a spot welded channel to hold the number plate.

 

Ron

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