Hi,

Anyone here of an m20 surging? While I drive the motorcycle feels like it surges or pulls. Goes away under heavy acceleration, not present at all when i pull in the clutch. ( i don't believe it is from the brakes.)

I just rebuilt the clutch and it seems fine. Had a local moron (my mistake) rebuild the tranny. Any thoughts?

It is a 1944 BSA m20 thanks for the help

email (option): jeff@infinitymedspa.com

Hi Jeff. How's your throttle cable. If it's trapped or incorrectly routed it could cause this especially when cornering

the other one is, regular lubrication(every 1000 miles or so) with a suitable oil such as cycle oil (not wd40)for smooth cable operation

i dont think its the cable since it is happening while just cruising down the straight street.

Could it be a carb problem?

Yes I think I know what you mean, I've had a similar thing with old bikes. Is it when you are cruising with the throttle in the same position and the bike doesn't settle at a constant speed..? If so, I would say it's the carb. I changed mine and it was a different bike.

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

Hi Jeff, You could try weakening the mixture in the cruising speed range...also check your mainjet size, it should be a 170...Ian

I had the same problem on a snowblower. Air leaks at the manifold gasket. Lean, rich, lean, rich......

email (option): britool51@hotmail.com

Snow, no snow, snow, no snow.. ...Ian

Thanks I'll check the gasket and reseal. I'll also double check the jet.

Yep that's exactly it. When I'm just cruising. I know the original Amal crbs are finicky. What did you switch it to? Thanks

We have the same problem when we use Kangaroo fuel ha ha;
on the other hand could you have fuel starvation?
Brian Forth

email (option): forrthy@picknowl.com.au

Similar experience, my carb nuts came loose, the action of the cable pulling the carb made it move about, sealing and opening up a gap in the gasket to the barrel, plus the carb itself wasn't running smoothly in its cylinder. Roadside repair soon confirmed..you guessed it, I didnt do my pre-ride checks.

One thing that I prob shouldnt admit to openly was getting the fuel taps round the wrong way, what I thought was closed was open etc., it had been a few months..this made a rather substantial difference and had similar reaction to what you are describing, so check your fuel taps are both open fully and that there is no crap in the pipes or tank blocking the fuel flow, just what I'd look for.

email (option): kit247@hotmail.com

You should only require one fuel tap. The other one will then give you a bit in reserve if you run out, with what is trapped in that side of the tank.
Also I think it was Rik who posted an easy way to remember ON and OFF. The side of the tap with the six sided top (HEXAGON) is the ON tap. So just remember hexag-ON Ron

email (option): ronpier@talk21.com

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

thanks to everyone. I resealed the carb with a new gasket and it is a lot better. i will check the jet this weekend. OIt might also be prudent to just by a new carb from amal. I believe they are making them again. Anybody have a reasonable idea if I want to go with a more recent replacement carb? Im getting the bike ready for normal riding and do not need it "show" ready

Hi Jeff...If you are not worried about originality the Amal Mk1 Concentric is by far the cheapest solution...they look different but function in pretty much the same way.You will need a 'concentric' throttle cable as well.....Ian

email (option): julie@wright52.plus.com

I just bought a brand new Amal 276 for my M21 engine. It cost £240 inc, VAT. Absolutely brilliant. The only criticism, is the chrome parts are bright instead of satin. But since I had just fitted some new satin chrome parts to my old carb, I just swapped them over. Ron

email (option): ronpier@talk21.com

Yes it's great that Amal are still making these carbs so you can keep your bike original. They will also make carbs to your specifications, and their technical team are very helpful if you give them a ring, and don't treat you like an idiot for not knowing something.

http://www.amalcarb.co.uk/default.aspx

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

I fitted one to my M20 when they first started reproducing them..set up was very quick and easy and it has run faultlessly ever since...Ian

email (option): julie@wright52.plus.com