My M21 after travelling less then one mile from cold begins to misfire under load and at any speed above about 25 Mph.

Bike starts easily from hot or cold.

Engine has good compression, point gap and timing checked and found to be good.

A new lead and spark plug were fitted but made no difference.

The fuel cap is vented correctly.

Fuel flows freely out of the fuel tap.

Correct 276 carby from Amal fitted about 500 miles ago.

I don't know the history of the magneto fitted to the bike but I am beginning to think this maybe the problem?

Any assistance greatly appreciated.

I would start by removing the carb for a strip and thorough clean. There are some tiny drillings in the jet block and carb throat that can be poked through with fuse wire and air line, which will require the jet block to be removed. Also take the float bowl apart for a good blow through. Ron

email (option): ronpier@talk21.com

Magneto problems are often condensor related and in my experience take a bit more warming up before they give trouble.

Could it be choke related, is the choke slide fully lifting?

Rob

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

That's a good point Rob. Are you pulling the choke lever off? ie lifting the slide? Ron

email (option): ronpier@talk21.com