Non starter when hot

[Captain Mike]

Hi I am running in my 1957 Plunger A0 and have an issue with it not starting when hot

During a cold start the old girls fires up 1st or second kick and then settles down ok, then I go for a run for 20 - 30 miles and then stop the engine, it will not start again, twenty kicks later, still no starting, I thought I had flooded the carb the first time this happened, but this does not seem to be the case

it seems to be when the motor has cooled down enough it will start again, I have not been happy with the spark from the magneto since I bought it as it seems fairly weak, and not a great big fat blue spark as I anticipated with a magneto, I have read that it may be the field wiring that is breaking down in the Mag

can anybody give some advice, and confirm if the magneto should have a large fat blue spark as I call it ?

Thanks in advance 

[Pete A10]

This sounds like classic magneto windings failure. Once the mag has been working and got warm the insulation breaks down leading to very poor or no spark. The spark should be bright blue and capable of jumping a quarter inch. I had the same on my A10 and ended up having to have the magneto rebuilt (£300+).
It may be worth stripping the mag off and cleaning the slip ring and checking brushes first but I wouldn't hold my breath. It may just have to be an expensive repair.

[JulianS]

Will not start when hot but starts when cooled down can also mean a failing condenser.

[Captain Mike]

Thanks for the reply's guys, much appreciated, after doing some research on magnetos/ repairs/ new ones, and pricing, I am going to convert to Electronic ignition, the cost is minimal compared to Magneto repairs, it maintains the magneto and looks original, and should be a fit and forget

I have already converted to 12 volts along with LED lighting and electronic regulator so I may as well go the whole nine yards

Reliability is paramount to me, and in any case if these things were available as upgrades in the fifties and sixties I am sure there would have been an uptake to make sure the old man could ride his Beeza to work and take the misses out at the weekends without breakdowns

Cheers

Mike     

[geraldhattrick75]

I had the same trouble with the magneto on my Velo Venom, and fixed it with one of these........

http://www.brightsparkmagnetos.com/easycap/index.htm

[EDDIE SIMPSON]

what size is the pilot jet?
although magnetos can be the problem i would experiment with a smaller  jet and use the choke to start when cold and see if the hot start is better.
i went down to a 15 pilot on my iron head a10 . i thought it was a modern petrol quality issue.

[Guitarzanbikes]

Experienced exactly the same problem with the iron head Flash combo the other week when it was a nice hot day. 50 mile thrash and stopped for a brew, wouldn't start then.Pulled the plugs, dry as a bone, 2 big fat sparks. Fuel evaporation due to heat i reckon, the old gel was working hard before we pulled in for a cuppa and you could fry an egg on the head! Had another cuppa, waited a bit and she started fine and ran ok. Have got a float bowl extension on my monobloc carb and a thick tufnol spacer between head and carb but the carb still gets really hot and bothered on days like this, in total contrast to the agro I had with the carb freezing up regularly on an A65 in freezing fog! I'd be looking at the carb.