Re: Changing spark plugs often

Hi Fabrizio. Three things:

It could be the magneto. Quite often old magnetos have an open circuit on the secondary coil or the capacitor (condensor) is faulty. When cold it works but when warm the problem causes the magneto to stop generating good sparks. After you stop and replace the plug, sufficient time has passed by for the magneto to cool down a little and start working again.

OR:

It looks as if the fuel mixture is very rich. When the engine is cool, the mixture works well, but with a hot engine the mixture is so rich the plug becomes sooted up and fails to spark. Check the jets for the correct value, the float height and see if the clip in the needle is in the correct groove. Alsoget someone to follow you and check for black smoke from your exhaust.

OR: The piston rings, especially the oil control scraper ring, have not bedded in orare broken or faulty. This will allow oil to pass by the rings and carbon up the plugs which will short out with all the carbon forming on them. Get someone to follow you as you ride the bike to check for excessive blue smoke from your exhaust.

Regards

Les

Previously tapia_fabrizio wrote:

Hello,

I am new to the club and own a 1949 ES2 500, the motor was just rebuild and it start very easy after few kicks, then runs well for 20-30 miles. After that it start misfiring until it turns off and also becomes very difficult to restart . Once the spark plug is replaced with a new one, there is no problem (the spark plug comes out wet and dirty). Does anybody has some idea what can be wrong or I need to fix?

Thanks

Fabrizio

Dear Fabrizio,

I'm afraid it is the windings on the magneto. In earlier daysmagnetos were manufactured utilising "Shellac" as an insulator for the windings. Over a period of years this insulation starts to break down under heat and whereas the machine will always start cold it becomes ever more difficult to start it hot because of that insulation breakdown. It happens on the twins too.

My advice is to not mess about any further. Remove your magneto and have it re-wound by a specialist and your troubles will be over.

Regards,

Peter Bolton