hi there , has anyone experience with running the bikes in high alpin regio? we try to make a trip in the dolomites and there are many old military trails up to 2000m. do we have to change main jets? greetings jarek

email (option): jarek@jareksgarage.de

Hi Jarek

I had trouble in the Austrian Alps with a melted piston on my M20, I was told afterwards that I should have rejetted the carb, but strangely they suggested a larger main jet, which I never understood, I would have thought that if you were drawing in less oxygen you should reduce the petrol to match???? Rob.

email (option): robmiller11@yahoo.co.uk

Jarek, BSA recommended reducing the main jet size by 9% for altitudes of 6,000 feet (1,800 metres), so a 10% reduction sounds about right for the higher trails. The problem is that if you re-jet and then have a steep climb up from an overnight stop at low altitude, your engine will be running too weak and that's asking for trouble.

I think it's safer if you just let the engine run rich at high altitude and take a couple of spare sparkplugs.

Chris J

For what it's worth I travelled a lot to Switzerland in the 60s and 70s on various bikes BSA, Panther and a Vincent, never found any need to change jets for travelling over the passes most of which were over 7000ft, suprising enough never had to change plugs either, you will notice a small drop off in power but thats all.

not that i am up to speed on carburettor settings but could you move the notch up or down on the needle to get different fuel air mixture

Raising the needle will only effect the middle range, with all the raw power of a M20 at your disposal you would be on the main jet all the way up the pass,personally I would leave the main jet running slightly rich, I would think that the extra fuel would help to cool down the piston.In 1965 I took a 1952 600cc Panther plus double adult sidecar and 4 people plus camping gear over the passes and into Italy, first gear all the way up but no problems.

Yes, all travelling in an M20 is full throttle!

ok guys, thanks a lot, i think i will take a 190 jet as a spare and several spark plugs. 170 is the original isnt it?

email (option): jarek@jareksgarage.de