AJS & Matchless Owners Club

Hi

I have a new Monobloc fitted to my Model 31. It starts well, ticks over nicely, the pickup feels clean, it doesn't spit back or backfire, and the plug colour seems OK. All good so far. But, when fully warmed up and you go from a very slight throttle opening to none, when trickling along in traffic for example, it doesn't seem to shut down immediately, but continues to rev for a couple of seconds, then die back to idle. I first suspected the cable (twist grip and cable are also new) or slide were sticking slightly, but they seem fine; replicating the throttle movement immediately after turning off you can hear the slide bottom out against the stop, and feeling the movement via the bellmouth confirms it. I'm sure I've had this many years ago on a different bike; could it be the fuel/air mixture when running on the pilot jet?

Thanks,

Malc

It does sound like something is sticking. It does not need much, twist grip, cable dry, sharp cable bends. Give the cable a good oiling. I have had cables come out a box dry. Just left them in a tin lid full of oily white spirit for a few days. Not got a cable oiler to force oil from one end till it comes out the other.

Could it be caused by a weak or broken spring in the avd/ret unit being slow to return?

You know what 'they' say? If you think it's carb, it's usually ignition and if you think it's ignition..........

Hi

Ladies first: Janet, it's a manual advance/retard magneto version, so it isn't that. I certainly know what you mean about carburation vs ignition though. Rob, it's certainly worth a go. When you say 'oily white spirit', do you literally mean white spirit with some oil mixed in?

Cheers,

Malc

Hi

To confirm Spriddler's diagnosis it may be worth seeing if the same effect is experienced if you momentarily open the throttle and then shut off. If it closes down as expected then Sprid is more than likely correct.

Regards Mick

MalcW wrote:Hi

Ladies first: Janet, it's a manual advance/retard magneto version, so it isn't that. I certainly know what you mean about carburation vs ignition though. Rob, it's certainly worth a go. When you say 'oily white spirit', do you literally mean white spirit with some oil mixed in?

Cheers,

Malc

Anything I have laying about Malc, even old sump oil. Some of those NOS cables are quite dry. Takes some time to get them slippery. I had the same problem with my 64 G12 CSR. On shutting down it took ages for the slide to bottom. At first I had probs with tick over setting. Get it right, or so I thought. The once cable was bit easier, shut down too much so engine stopped. Although at first it ran too fast. After a few miles, problems when it loosened and engine keep cutting at lights etc.

I can tell you exactly what the problem is, it's the new carb and excessive slide to body clearance! Every new carb I've had has had the same issue and the suction on the inlet cause the slide to pull towards the motor tipping it slightly causing it to hold up. Retarding the ignition slows the motor and allows the slide spring to overcome the suction and lets the slide drop. When the motor isn't running there is no suction on the slide and it drops to the bottom every time with a reassuring clink.

Can it be overcome by fitting another slide?
Tony

raffles wrote:Can it be overcome by fitting another slide?
Tony

Tony I meant to add that the other issue is that as the clearance is too big it let's more air in altering the mixture which causes faster running as it leans it out too much. Depending on how bad the clearance is it can be overcome by fitting a Surrey cycles oversize slide I used a 389 3c on my CS. 3 being the cutaway and C indicating it was 3 thou oversize. Not sure how many Michael has left though.

That's interesting. I've just measured it using the scientific method of sticking my finger in the air intake and wiggling the slide. There is indeed a movement; very slight, but more than the old Concentric it replaced. In all other respects it's working fine though.

Malc