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Re: 1932 BSA 500 cc side valve starting problem

Get a can of carb cleaner , remove the spark plug and put a SHORT shot into the cylinder.
Replace the plug and give it a good kick
You might need to give it a couple of them.
Bike fires = fuel or valve problem
Bike does not fire = spark or timing problem.

Assume it fired, repeat but this time squirt the carb cleaner through the carb.
Bike does not fire = valve timing problem
Bike does fire = carb problem

NOTE I said carb cleaner, not starting fluid as starting fliud can ignite way too early.
I like to put a red in line spark tester on the plug so I can tell when the plug is firing and watch it flashing when the engine is turning regardless of weather the engine s running or not.

email (option): bsansw1@tpg.com.au

Re: 1932 BSA 500 cc side valve starting problem

Thank you for all your help. Yesterday I had another go at starting the bike. I made no alterations other than trying the ignition level and air lever at different positions (which I had done before).

After two minutes of the same back fire and failing to run it came to life! I quickly put my helmet and gloves on and set off for a ride. For the first mile and a half the engine was popping, but at the two mile mark the engine smoothed out and I started to enjoy a well mannered bike. After four miles I realised that the vibrations were undoing the nut on the ignition lever, hence I returned home before I lost the nut and created another job.

When I got home the bike was running fast at ideal, can I resolve this by turning in or out the air screw on the carburettor?
The bike started when the ignition was fully retired and the air level was full closed. I would like to think that this was to answer to my problem; however I know that I had tried this combination before with no luck.

What do I take from this small victory to the journey to understanding my bike and having an easy to start smooth running bike, ……. well just these points:

1, Air fuel is getting through to the engine
2, The new spark plug works fine
3, The engine timing works

email (option): jonathan.billington@blueyonder.co.uk

Re: 1932 BSA 500 cc side valve starting problem

Hi Jonathan

A loose nut on the advance/retard lever is probably not helpful as any vibration means that the ignition may retard of its own accord (assuming you have a tight wire advance mag).

I would ignore the choke i.e. make sure it is in the fully open position.

What condition is the carb in? The main reasons these bikes are difficult to start are due to either a worn out mag (not the issue here), a worn out carb or poor timing.

Regards

Pat

ps Once your bike is running, fully advance the ignition and leave it there (unless it pinks a bit going up steep hills). Running any bike retarded is not good for them and particularly bad for side valves.

email (option): sacombsashtrees@hotmail.com

Re: 1932 BSA 500 cc side valve starting problem

Thanks for your post Patrick.

I cleaned and rebuild the carburettor and to my novice eye it looks clean and functional.

Your point about running the bike fully retarded has been noted; I understand it can result in the exhaust valve becoming too hot, hence causing new problems.

email (option): jonathan.billington@blueyonder.co.uk

Re: 1932 BSA 500 cc side valve starting problem

Hi, I've having loads of issues with the starting on my M20. Try reducing the plug gap to 15thou. Mines started with this

Re: 1932 BSA 500 cc side valve starting problem

Jonathan,

I'll share my own experience here. My WM20 has a rebuilt by the REME engine, unused til I fitted it. Good spark, nice clean carb. It didn't want to fire up, and back-fired through the carb a couple of times. Like your bike it did eventually start and ran somewhat poorly for a while before settling in to a nice steady run.

After some frustration I discovered that I was over-tickling the carb, effectively flooding the engine. Now I simply turn on the fuel, don't touch the tickler, set the advance at about 7/8 advance, no choke needed. It usually fires on the first kick.

I was judging this bike by the standards of my other pre-war rides, where flooding the carb usually permits an easy start. This is not always the case!

I hope this helps.

Allan

email (option): allanmatchless@yahoo.com

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