tgh30 Posted December 15, 2013 Report Share Posted December 15, 2013 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 Quote Link to comment Share on other sites More sharing options...
big_red_bike Posted December 15, 2013 Report Share Posted December 15, 2013 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. 1 Quote Link to comment Share on other sites More sharing options...
tgh30 Posted December 15, 2013 Author Report Share Posted December 15, 2013 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 Quote Link to comment Share on other sites More sharing options...
b40rt Posted December 15, 2013 Report Share Posted December 15, 2013 (edited) 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, 2013 by b40rt Quote Link to comment Share on other sites More sharing options...
laird387 Posted December 15, 2013 Report Share Posted December 15, 2013 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. 1 Quote Link to comment Share on other sites More sharing options...
carl ekblom Posted December 15, 2013 Report Share Posted December 15, 2013 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. Quote Link to comment Share on other sites More sharing options...
jon v8 Posted December 15, 2013 Report Share Posted December 15, 2013 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.... Quote Link to comment Share on other sites More sharing options...
laird387 Posted December 16, 2013 Report Share Posted December 16, 2013 To Jon v8, When I bought Peter Gaunt's Ducati trials special, since we were old friends, he warned me that; "The carburation needs finishing, I just can't get it to pull reliably - so don't come back complaining - if you take it, you fix it." He was, of course, accurately reporting the way the bike performed. Using it, say, on an uphill section it would pull away like a tractor, then when you came to the easy turn at the top before starting back downhill it would just splutter and die on you. Trying to get it to tick-over reliably was my first goal, but fiddling with every aspect of the carburettor had little or no improvement - then my electronic engineering background made me decide to rule out every concievable variable first, then try the carburettor. Peter had cleverly fitted the flywheel ignition system from a 160cc Ducati twostroke on to the desmodromic 350 fourstroke, so i eliminated that by running a lead from the points on the bike to the coil on my car alongside and then a long lead to the plug cap - using the cars coil ignition !!! Kicked over the Ducati, started first prod and settled to a tick-tock reliable tickover - never touched the carb. Light dawned, swopped back to the flywheel ignition, the bike coughed and spluttered and just would not tickover. Out came the soldering iron, a small rechargeable battery was fitted behind the front number plate, the ignition coil from a Triumph Thunderbird under the petrol tank - then prodded the kickstart. Thump, thump, steady as a rock. Took it out to my favourite practice ground in Adel woods, swooped up and down, in and out of the streams, over the rocks, never missed a beat. The bike was a revelation, utterly transformed. After that I started rebuilding my own magnetos as part of my restorations. Quote Link to comment Share on other sites More sharing options...
tgh30 Posted December 16, 2013 Author Report Share Posted December 16, 2013 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 Quote Link to comment Share on other sites More sharing options...
trickymicky Posted December 16, 2013 Report Share Posted December 16, 2013 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. Quote Link to comment Share on other sites More sharing options...
tgh30 Posted December 16, 2013 Author Report Share Posted December 16, 2013 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 Quote Link to comment Share on other sites More sharing options...
trickymicky Posted December 16, 2013 Report Share Posted December 16, 2013 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 Quote Link to comment Share on other sites More sharing options...
tgh30 Posted December 16, 2013 Author Report Share Posted December 16, 2013 Understood. Thanks for the reply, fingers crossed somebody with a running Matchless will be along soon. Tim Quote Link to comment Share on other sites More sharing options...
old trials fanatic Posted December 16, 2013 Report Share Posted December 16, 2013 BIG JOHN Quote Link to comment Share on other sites More sharing options...
big_red_bike Posted December 16, 2013 Report Share Posted December 16, 2013 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. 1 Quote Link to comment Share on other sites More sharing options...
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