Hi Guy's,

I own a beautiful 1961 Matchless G3C that isn't running at it's best. I think it's the carb but before I go out and buy a new carb I wondered if anybody could recommend somebody in the midlands that would be able to tune my bike? It ias a AMAL MK1 Concentric carb, after about 5 mins of running it appears to run out of fuel and you have to tickle the carb again to be able to start it as if it is getting air into the carb from somewhere. I have a Domino fast action throttle on it and wonder if that contributes to the problem as when you open it up quickly it appears to jump straight to the main jet.

Desperately want to get her running nice as at the moment she is no fun.

Any help is appreciated,

Tim

Hi i would first check the fuel flow from the tank to see if the tap or vent are blocked.If there is a good fuel flow from tank check the fuel filter on the carb in the white plastic housing where the fuel pipe pushes on.

Thanks for the response. Yes, the tank was very dirty, with bits of paint and alsorts of other muck. I have flushed it out now, the filter is old and whilst it doesn't look blocked I will get it replaced in the new year. The vent is a good call. I will investigate that tomorrow.

Thanks again, your help is appreciated.

Tim

Nice bike, check float level. If it's original carb it will be worn, which won't help running.

A heat shield is a easy addition to make, and would help eliminate fuel boiling.

I would also change to a slow action Domino anyway.

Edited December 15, 201312 yr by b40rt

I support b40rt

Concentric Mk1 when old gets worn in throttle and throttle body causing lean mixture and erratic idle. Only replacing the throttle doesn´t help much. Both the throttle and throttle body have to be changed.

Hi,

Having owned and ridden similar machines I would strongly recommend looking at the spark before going into any expense with carburation, especially since it already has a more modern carb. than original.

Good luck.

Excellent advice,my 1950 rigid 350 Ajs was never quite right at idle/low revs.I could never get it spot on.When I took the engine apart for a rebuild I mounted the mag up in the lathe with a rubber drive coupling.With it spinning at 300rpm there was a lovely fat blue spark at the attached plug.I was monitoring all this with my oscilloscope,and all was good.I then fitted a piece of hose over the end of the plug to apply compressed air.The spark trace on the scope then all but disappeared.100psi was enough to kill the spark at that speed.

The mag is now away being rebuit....

Laird 387 & Jon V8, Thank you for your responses and the examples of how you cured your bikes. Lairds description of how his Ducati was running sounds very similar to my issues. However, your testing and resolution are born from a genius that I sadly lack. The best I can hope for when checking for spark is to whip the plug out and look. However, I have just downloaded a magneto tips document from the AJS and Matchless owners club website. I will give that a read tonight and see where it takes me. I wish I had your genius the thought of being out of my comfort zone is not a nice feeling but desperately want my bike to run as sweet as I know she can, especially as the the first round of the Yorkshire classic is in 4 weeks or so, with Christmas in the middle it doesn't leave me much time.

Once again many thanks,

Tim

The carburettor appears to be a 900 series, if it is, its too big. I would try something like a 624, or whatever the AMC riders on here are using, together with a slow action throttle.

Hi trickymicky,

Yes your right it is a Concentric Amal 928. The original specification is a Mono block Amal 376/59t. I suppose it needs to be the equivalent concentric of the 376. My sums suggest a 26.98mm carb which would be either a 926 or a 928 but would need somebody to verify before I spent the cash.

Tim

Tim

The 928 (28mm) is the smallest available in the 900 series. Below that it is the 600 series and you have a choice of 20,22,24,26 and 27mm. 900 series carbs are physically bigger than the 600s', and the general trend is to use the 600,sometimes in smaller sizes than originally fitted. Hope this helps,and as said previously maybe one of the regular riders will be along to tell you what they use

Understood. Thanks for the reply, fingers crossed somebody with a running Matchless will be along soon.

Tim

BIG JOHN

Hi as mick says could be to big a carb but it should still run with the carb you have.If by tickling the carb it restarts you are not getting fuel to the float bowl.Try running the bike untill it cuts out then turn the fuel of quickly then remove the float bowl and see how much fuel is in it.

What big red said, sounds like fuel starvation. Nice looking bike, but if it were mine I would have a foam type pod filter on there not just a mesh bell mouth.

What big red said, sounds like fuel starvation. Nice looking bike, but if it were mine I would have a foam type pod filter on there not just a mesh bell mouth.

Agreed but I wouldn't have either I would have as big as possible considering space available a alloy fabricated air box with a proper modern replaceable filter element fitted. Could still be made to look period but why oh why would you want to fit that awful bellmouth to a Classic bike that has had so much spent on it? spoil the ship for a haporth of tar ?

Then again it's your bike so you do as you like.