I have found that the fuel filler cap tends not to seal 100% on these bikes.

It could be a vacuum in the tank, if so make sure the little pin hole on the filler cap isn't blocked.

To eliminate this as a potential problem, you can undo the filler cap whilst riding just as it begins to splutter. If the bike springs back to life, then problem solved.

If this doesn't work, then I would think about the condenser.

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On side valves particularly, the valve that gets hottest first tends to be the exhaust valve.

When the exhaust valve sticks, it tends to stick slightly open. Therefore, the symptoms tend to be popping and banging from the exhaust pipe.

email (option): sacombsashtrees@hotmail.com

I would class a sticking valve as an unlikely cause...Unless you have just had the engine rebuilt and the valve/stem clearance was too small...

In 45 years I've never had the problem or met anyone who has...(though no doubt someone has!)

If it's the mag, you will find the spark is strong and blue in colour when the mag is cold but weak and pale/white in colour when the mag is hot...

If you suspect the mag try closing the plug gap down a little to see if that helps at all....012"-.014"...

My advice would be to get the mag overhauled immediately if you have the symptoms outlined above...

On the basis of starting with the easiest thing first I would try the petrol cap seal first....Ian

Hi guys,

Sorry, I should have said that the mag was a brand new (fully refurbished) replacement (fitted especially for the Normandy trip), as my previous one did have a crap condensor... it is now waiting to go for refurbishment as well.

The spark is crisp when hot or cold now :-)

I'll check the breather hole once more as has been suggested, but, has anyone ever heard of adding kero/parrafin/diesel to the tank before?????

Thanks for the suggestions folks :-)
Ian

email (option): fozzie001@hotmail.com

I've never done it and haven't experienced any fuel related running problems with my M20...I just run on the standard lead free fuels available in garages...

I've not had problems with French fuel either over numerous Normandy trips...Ian

I have had these symptoms on several bikes and even my van when the diesel pump got blocked. The bike would run fine but the fuel wasn't filling up the float bowl as fast as I was using it. Then you stop and wait and the fuel fills up the carb again, so it runs again. Had this happen on my 16H, I cleaned out the fuel lines and the tank as there were fine black particles in it. Also drain the float bowl and check for bits. Another fuel starvation problem I had involved new petrol taps. Once used the rubber/cork swelled reducing the flow, I had to run an 1/8" drill bit by hand up it to open up the hole. So take the fuel line off and make sure you have a good flow from the taps. Have you tried running the bike with both taps on?

email (option): horror@blueyonder.co.uk

Hello Ian.

Do you have a "Paper" petrol filter anywhere on the line?
In the past, in order to stop bits and rust coming out with the petrol tank
To block the idle jet again and again, I fitted a small car petrol filter.
When driving in the city all was fine, but on the motorway, the petrol
Could not pass the filter fast enough to cover the petrol consumption,
As these filters are planned to be used in systems with pump, not gravity,
So I had the same symptoms.
I ended up fitting a large filter (about 2" in diameter) and that done the trick.
There are also mash inline filter which has no resistance,
But they usually block only bigger particles.

Noam.

email (option): noam10@gmail.com