Hi I have just completed restoring a 1942 BSA M20 and me and the other guy that I am working on this thing with have had a very difficult time trying to get this thing running. The engine had been fully rebuilt and has very good compression. The mag has been rebuilt and we have taken it off and re tested it everything checks out just fine. We set the piston to 7/16 before TDC on the compression stroke. The bike ends up building to much compression to be able to kick so we relieve the cylinder pressure. We have double checked everything and think it to be a timing issue or the point gap but have se the gap like instructed. If there is anything that anybody could tell me because I'm getting tired of pulling this thing apart. Like I said the only thing that I can think about is that the ignition timing is off compared to the engine timing, but I set it like it said in the manual. Thanks

email (option): bjsullivan23@ymail.com

Barrett you need to be sure the spark is happening at exactly the right time. If you have the correct mag, the adv/ret cable will be at the back nearest the battery ie, tight wire. Set the mag at full advance by pulling the handlebar lever fully towards you. The points should be just starting to open when the piston is at 7/16" BTDC on compression stroke. Sometimes it can take a good few goes to get it right by keep removing the pinion and re setting. Double check each attempt by turning the engine over two revolutions till the points gap is just breaking (I use a 1 1/2 thou feeler) and then check where the piston is. It's best done before you put the head on. Otherwise a marked prodger down the timing hole. As an indication the points will be turning clockwise as you look at them and breaking at around 10 o.clock. Then double check you have a spark by earthing the plug against the engine/mag and spin the engine to see a nice blue spark. After which it is probably a fuel problem if it doesn't start.
Sorry to go over stuff that you probably already know about. Just going back to basics. Ron

PS if your mag was professionally rebuilt. the points gap should have been set at the correct 12 thou.

email (option): ronpier@talk21.com

Hi Barret...There is a comprehensive piece on ignition timing in the 'Technical Section' of the website...It may give you more insight into what is going on...
When you are absolutely happy you have the timing set correctly, if you still have problems you may need to look at carburation/fuel.

Incorrectly set ignition timing is a common problem however, as it can take some practice to get the technique just right. Firstly though, you need a firm grasp of the method and theory....Ian

email (option): ian@wright52.plus.com

Hi Barret...There is a comprehensive piece on ignition timing in the 'Technical Section' of the website...It may give you more insight into what is going on...
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As a newby to magneto ignition Ian's article in the technical section sorted my starting troubles out when I first had my bike. You'll find getting the timing spot on make a big difference in how the bike runs.

Best of luck.

Stuart

Pleased to hear it was helpful Stuart....Ian

email (option): ian@wright52.plus.com