Hot Start Problem

[Billington]

My 1932 BSA W32-6 500cc side valve will not start when the engine is hot. It will start when cold with just one kick and run beautifully, however if I stop the engine and attempt to restart it when it is hot it will not start.

I had this problem in 2017, which I solve by having the magneto rebuilt. I’ve done approximately 800 miles since the magneto was rebuilt by Tony Cooper (I believe he is now retired).

Could the magneto have failed again with such little use or should I look for other issues. I would be grateful to hear your kind advice and details about how to diagnose this and correct issue.

[R]

Sounds like a failing condensor again, doesn't it. !
Do you know what the rebuild used - not a NOS one, we hope. ?

Another possibility is vapour lock.
Have you checked to see how warm the carb/manifold is when you pull up.
Those heat insulating tufnol type gaskets were added to many a model,
to help prevent this happening in hot weather.

So if you pour icy water over the carb and it still won't start, then try it over the maggie.
Preventing water ingressing to inside the works - a tricky situation.
Have fun, tell us how it goes ...

[33d6]

Of course the magneto could fail after little use. Age and how it has been stored since last done can have serious consequences regardless of mileage done.
I’m currently amusing myself with three radio controlled helicopters. All N.O.S, all received in their original unopened packaging, all looking perfect but all non running due to battery failure through sitting around for the last ten years or so. Electrical equipment can do that if left sitting. Look good externally but moulder away internally. Very frustrating but that’s how it is.
As R says it could also be vapour lock. Side valve engines do tend to run hotter than their OHV equivalent and I have seen some poorly thought out fuel line arrangements as well as R’s failure to fit a Tufnol heat barrier twixt carb and cylinder.
Nevertheless I tend towards electrical failure as my own experiences with vapour lock have been on stinking hot summer days with the engine smelling like a fifty year old fish and chip shop on a busy Friday night. Not just a mere hot start issue.
Tell us how you get on.

[john.k]

Fail to start can also be flooding of a hot motor ...........I diagnose start problems with a can of starting spray ......this stuff will fire with flooding or with fuel starvation .......but it wont fire with no spark.

[Billington]

Thank you everyone for your kind advice I will try your ideas.

[Billington]

Based on your diagnostic advice I went on a long ride. The air temperature was 26°C, 69% humidity (hot and sticky). The bike started easily on the second kick, then ran beautifully.
I then stopped the bike at the top of the hill an immediately attempted to restart the bike, however it simply would not start, not even any signs of firing. So I tickled the carburettor until fuel was seeping out of the bottom wholes, then kicked it over but it still refused to fire. So I put the bike in second gear rolled it downhill until it picked up speed then let the clutch out, it started and rode all the way home without any hesitation.

When I got home I stopped the engine and immediately attempted to restart the engine, but again it would not fire up. I then sprayed some Holts Easy Start in the carburettor at which point it started and ran without any problem.

About 3 years ago I started to have issues when running the bike at temperatures over 20°C. After just under 2 miles the engine would stutter and come to a halt. The carburettor would be very hot, hence the petrol had become so hot it vapour locked the carburettor. I was using E10 fuel (in the UK this means it can have up to 10% Ethanol). I resolved this by using E5 in a see through container then removing the Ethanol by employing the water method (Ethanol is hydrophilic), after 2 days I remove the water, leaving just fuel. I also added a 6mm Tufnol spacer. Finally, I changed the route of the copper fuel line from the fuel tank to the carburettor from behind the cylinder head to the right-hand side, where it could be in the air stream.

Because the bike started when rolled down hill I thought that this pointed to the condenser, however because the bike will start on Easy Start, I’m not sure. What are your thoughts?