My sons "new" AJS Model 20

Information relating to the Matchless G9 or AJS Model 20 500cc twin
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Re: My sons "new" AJS Model 20

Postby Janet » Wed Jul 19, 2017 9:30 am

SPRIDDLER wrote: Here's our 'Adverts Officer' Clive at 2,400m on his 350 en route to Milan, 2 up. Maybe he can comment on the effect of altitude.....
He seems to have lost his passenger. :o
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Re: My sons "new" AJS Model 20

Postby SPRIDDLER » Wed Jul 19, 2017 9:44 am

Janet wrote:
SPRIDDLER wrote: Here's our 'Adverts Officer' Clive at 2,400m on his 350 en route to Milan, 2 up. Maybe he can comment on the effect of altitude.....
He seems to have lost his passenger. :o



Ta-daaahhhhh!
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Re: My sons "new" AJS Model 20

Postby Daveinater » Wed Jul 19, 2017 9:51 am

G15 Roy wrote:are you sure that you have the chock turned off.

I'm pretty sure yes. The mechanic told us the choke would not really be necessary as it starts on the first kick. In fact, he tightened the choke lever so much that it wouldn't be easily moved. I'm out flying right now but I assume the choke is disengaged with the lever fully in?

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Re: My sons "new" AJS Model 20

Postby Daveinater » Wed Jul 19, 2017 9:52 am

Any quick and easy way to properly set the mixture? Is the mixture screw on the right or left side of the carb?

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Re: My sons "new" AJS Model 20

Postby SPRIDDLER » Wed Jul 19, 2017 10:42 am

Daveinater wrote: I assume the choke is disengaged with the lever fully in?


Not sure what you mean by 'in' as the choke lever on the handlebars rotates. The choke slide in the carb is sprung loaded and defaults to the choke 'on' position.
To put the choke 'off' the h/bar lever must be rotated (turned) so that the cable is pulled tight. This lifts the choke slide to the 'off' position.

The mixture is determined principally by fixed jets which are changeable by replacing any them with another of a different size.
The Pilot jet setting is adjustable by screwing in or out the Pilot jet screw. The basic position for this is around one and a half turns anticlockwise from the fully 'in' position. Th'engine is only supplied with fuel from throttle shut to about 1/4 turn open via this Pilot jet.

You have a Monobloc carb. There are other adjustments which are fully detailed in the full tuning instructions here:

http://amalcarb.co.uk/downloadfiles/ama ... d_Tips.pdf

A couple of pics...
Choke 'Off'. (For normal running). Cable pulled tight
2017-07-19 Choke 001 (480x319).jpg


Choke 'On'. (If necessary for cold engine start up). Cable slack (i.e 'released').
2017-07-19 Choke 011 (480x319).jpg
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Re: My sons "new" AJS Model 20

Postby Rob Harknett » Wed Jul 19, 2017 12:08 pm

Not sure if this model has auto advance and retard< if it has a manual A/R lever that needs to be set fully advanced.

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Re: My sons "new" AJS Model 20

Postby Daveinater » Wed Jul 19, 2017 1:09 pm

Hi guys,
Yes, sorry, my description wasn't so good there. I will have to double check the lever positions. I think he set the choke lever in the OFF position and tightened it there, saying we wouldn't need it. As for the timing lever, yes this has one as well, and we haven't messed with it much but it is in the "fully forward" (towards the front of the bike) position. I think he said if we pull the lever, we would advance the timing, so that would mean it's been fully retarded. (I may have that basackwards. Old age does that to a guy. Lol)

I will double check these when I get home.

As for the mixture, sound like we need to re-jet the carb. SIGH. Probably not something I'd try myself. Is that a science and are the jets readily available?

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Re: My sons "new" AJS Model 20

Postby Janet » Wed Jul 19, 2017 1:32 pm

A bit of advice from someone who has spent a lot of time messing with non-functioning* motorcycles but still knows very little. When you're chasing a fault of any description, only alter one thing at a time. Before doing so, make sure you know how it is before you start, eg a choke setting or points gap etc Then you'll see whether the change made it (1)better, (2)worse, or (3)no impact. If (2) or (3), you can put it back to the way it was and look for something else.

*Some of them didn't even function before I started messing.
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Re: My sons "new" AJS Model 20

Postby Mick D » Wed Jul 19, 2017 1:54 pm

Sound advice there Janet

Regards Mick

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Re: My sons "new" AJS Model 20

Postby SPRIDDLER » Wed Jul 19, 2017 1:55 pm

Daveinater wrote:. I think he set the choke lever in the OFF position and tightened it there, saying we wouldn't need it.

Refer to my photos and establish positively how to set the choke.

..we haven't messed with it much ..... I think he said if we pull the lever, we would advance the timing, so that would mean it's been fully retarded.

You need to be 100% sure what you're doing with this. The setting should be at fully advanced for riding around. IF you are riding with it retarded it'll feel dull and as if the brakes are binding (and th'engine will overheat).

As for the mixture, sounds like we need to re-jet the carb. SIGH.

Whoah! Let's not go there. If the carb has been correctly jetted for the Model 20 (it probably has) it's unlikely to need any jet changes made. Just familiarise yourself with the carb tuning info in the link that I gave you. Don't change anything inside the carb (or as Janet said, don't change more than one of anything at a time) or you'll be needing to call in here:
Shit creek paddle stores.jpg
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