Hi All.
It's a trip down memory-lane for me - I've just bought a '44 WM20 as my Dad rode & istructed on them during the war and am loving it. It's just today's starting problems that are proving difficult.

I went for a 10-miler this morning and it started perfectly. 10 minutes after returning home it didn't want to know. Yellow spark from the plug and also,the plug remained dry despite various tickles and a quick carb strip-down.

It's been pretty hot today - 26 deg c - does that usually create problems with vaporisation?

Various positions have been tried on the adv/ret & choke but still no life.

Worst of all, I had the wife and kids loaded into the car as there was a classic show 2 miles from our door and wanted to debut the WM20. The BSA had to stay at home and I had to take my trusty CD175!

Lee.

email (option): lee@twowheelstested.co.uk

see how well it starts when cold it could be the magneto but always start a the cheapest thing first they do suffer with fuel vaporisation i have a 1/4" spacer between the cylinder head and carburettor plus a metal spacer about 1mm thick that is about 10mm larger all round so that is looks and acts like a cooling fin

email (option): roger.beck@node6.com

Hi Lee... Fancy meeting you here! You may experience fuel vaporisation problems if your M20 does not have a tufnol heat insulation spacer fitted between the carb and the barrel. It should be about 1/4" (6mm) thick. If you don't have one you will need one..they can be obtained from Martyn Bratby or Surrey Cycles to name just two carb specialists. Probably also from Draganfly Motorcycles.
If you do have one you shouldn't experience any problems in that area whatever the temperature.
The Magneto is another issue...The commonest fault with these is condensor failure. Symptoms of this are a failure of the spark when hot. You need to test this a couple of times to be absolutely sure there is a problem as replacement of the condensor is a professional job.
Take the bike out a couple of times on a circular route that is long enough to get it up to full working temperature. Check the spark before leaving and on your return (while everything is still hot) to assess the strength and colour of the spark. If you have a good blue spark at the beginning and a weak, pale white/yellow spark at the end there is probably a problem.
When the engine has completely cooled down check the spark again to see if it has improved..
Let us know what you find...Ian

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

If when you are out and it doesn't restart when hot, try knocking the plug gap down to 10 thou it may give you enough spark to get home

Hi Ian..that was why I suggested a 'circular' route that begins and ends at the garage ...Ian

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

Thanks all. I'll give it a go tomorrow and keep you posted on the results.

email (option): lee@twowheelstested.co.uk

Carry a can of spraystart with you as an experiment.

You'll find that even though it is hot, the fuel evaporation takes effect, try tickling it again.My last one was reliable as hell, but needed tickling hot or cold

email (option): davmax@ntlworld.com

Using the tickler (or effectively choke) when the engine is hot would surely indicate another problem?
Possibly weakness of the pilot setting and/or a worn slide.
A hot engine should not require enrichment to start it. I never use the tickler at all when the engine is hot on any of my bikes...Ian

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

A guy at yesterday's show recommended fitting an inline device on the HT lead called, possibly, Sparkrite(??). Not historically correct and is this simply masking another problem, or a god-send for the older bikes?

email (option): lee@twowheelstested.co.uk

Hi Lee..A waste of time if there is a magneto problem. There used to be and probably still are 'spark booster' products along these lines on the market..the argument was that an additional gap in the lead required a 'build up' of the electrical energy for the spark to jump the gap...or something like that..Unsurprisingly they were never fitted as original equipment by anybody. I saw something the other day that was supposed to boost power by increasing the turbulence in the inlet port...it was a bit of bent tin that fitted between the air filter and the carb...a joke product supplied by conmen.
Now where is my bottle of Doctor Quacks muscle improvement and anti ageing liquid? ...Ian

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

Hi Lee . A quick fix if you've got a vapourlock problem , in case you havent already been given this advice , is open the petrol filler cap so the fuel tank can 'breath' freely , open the throttle wide and boot the engine over at least ten times to clear the vapour from the system , then with the petrol cap still open tickle up the carb , and if it wont tickle , ie is dry , repeat the whole excersise until you get fuel in the float chamber . Ive had problems of this nature through lack of carb heat spacers , etc , or just because the weather is very hot , but when you're stuck out somewhere these little tricks can come into their own , Regards , Leif .

email (option): leifevans75@yahoo.co.uk

If you'll pardon the expression, first things first. You've just bought the bike, so the plug was fitted by a prior owner? Is it the correct heat range? The symptoms you describe are more consistent with a wrong heat range plug than anything else.

email (option): jonny.rudge@verizon.net

It came fitted with a BH8S. Am I right in thinking it should be a B7ES?

Hi Lee...B6HS...Ian

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

Thanks Ian.

Lee.

email (option): lee@twowheelstested.co.uk

Or better still "Champion L86C" IMHO!

Ron

email (option): ronpier@talk21.com

I agree Ron..I always use Champion plugs. However, the slanty eyed NGK plug is easier to source from the local Jap bike shop...Ian

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