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[Stedman]

I have a 1952 350 Bullet, which starts first or second time when cold, but after the bike gets hot after say 15 / 20 mins of running, if I stop the engine it will not rstart again until everything is cold again!? Anyone got any ideas as to what could be the problem?

[Dennis C]

One of the most likely things is that the Magneto needs attention, rewind, new condenser etc, check for a weak spark when hot.

[Beezabryan]

As said by Dennis = Mag Shagged

[John J]

Hi, The mag. could need remagnitising.

[Beezabryan]

The mag is still shagged and needs specialist attention. Remagnetising is not a home shed fix.

[Les H]

Just before you whip off the mag. Take out the plug when cold and check the spark with a NEW plug on the HT lead but left unfitted. Make a close note of how strong the spark is. Put back the old plug and keep the new plug in your pocket. When the bike is hot and it doesn't start, take out the fitted plug and once again use the new plug as the spark check. Run the test again by kicking engine over at the same speed as the first test and check or compare the spark. The results are obvious as to whether your mag is playing up...or not.

[Anders F. R.]

Been there, done that. My 1953 Model G had just the same symptoms, and the cause was the well known "old-magneto-that-doesn't-work-when-hot-syndrome" ....................................

As the others say, the magneto is likely to be the cause of this. What happens is that the insulation on the windings crakcs or something when it gets old. When it heats up, it short circuits and malfunctions. It may still run, but the spark is weak. As the voltage, and thus the spark strength, from a magneto increases with the rpm, the spark is too weak (or completely gone) when you try to kick it over when hot. When it cools down, it recovers.................................

Try the test that Les H describes. My best guess is that you will get a much weaker spark from the hot magneto, if any at all.....................................

If so, take the magneto to someone that can refurbish it. I did, and it has been just fine since then. It really takes a specialist to do it properly. .................................


Regards, Anders F. R.

[simon]

Dave Lindsley will rewind the mag for you if it needs doing although check to see if the spark is weak when hot, there is alwats the chance that you mixture is too rich. Otherwise you can get someone to megga it for you to see if the windings are breaking down if they aren't it might just be time for a new condenser, the old fashioned version you can replace with a solid state one without too much of a problem.

[Roy]

I agree with Les. I had exactly the same problem on my 1938 model and fortunately it was the plug. Apparently with age the ceramic insulator develops hairline cracks which shorts out the spark when the plug heats up. Good luck.