poor running / tickover G2

Information relating to the Matchless G2 or AJS Model 14 250cc Lightweight
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poor running / tickover G2

Postby paul miles » Fri Jun 06, 2008 7:49 pm

Hi all,
I have a G2 CSR which Im trying to ready for road use.
The old girl suffers from rough idleing even when warm,sometimes racing slightly then slowing almost to a stall. I have cleaned and checked the carb (389) as well as I can, replaced points condenser and changed the coil & HT lead (silicone one from a car)which I know isnt ideal but Im trying to eliminate things. The greatest improvement came when I replaced the Champion plug (N5C)to a NGK B6ES which certainly improved overall performance. Is this the right NGK plug???? as I read somewhere that they can clash with the top of the piston, I measured it as best I can with vernier gauge against the N5C and it seems the same length. Does the type of plug cap matter on this lightweight or not?

As you blip the throttle it seems to hesitate only slightly to pick up and omits a very very small amount of Black smoke,Once up the rev range a bit the smoke turns white again only just noticeable but still there none the less..... I think its running a bit rich as it struggles to rev freely towards the top end of its limit when tested.
I know that once its on the road I can fettle with it further but I would like to try & get it running better now (Mr impatient or what !)

Any comments most welcome
Regards
Paul M

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poor running / tickover G2

Postby Biscuit » Fri Jun 06, 2008 8:55 pm

I carried out some experiments and found the the outer electrode clashed with the inlet valve. The solution was to lightly centre punch the body (or any other mark to taste) in line with the point where the electrode is fixed to the plug end, when screwed in it can be seen where the electrode ends up, if in line with the inlet valve then you have the problem, if you have a twin, swop the plugs around or if a single try another plug. You could try another washer on the plug. I have seen it written that if the gap faces the inlet valve (which is what we are after) then you get better combustion.




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poor running / tickover G2

Postby bjork » Fri Jun 06, 2008 9:10 pm

Hi Paul, assume you've checked the obvious things like sticking throttle slide or cable already, then have a look see if the slide or body has much wear in it. If you stick your finger under the slide you can check it for movement backwards and forwards. The most wear seems to happen just off idle. These carbs have a little movement as new, but if the wear is much at all you can get some of those symptoms.
I would also get rid of that silicone HT lead asap! The car you borrowed it from has a higher energy system and will cope with dodgy leads better than old lucas stuff at 40+ years. And silicone leads are famous for being infamously crap.
To help you stop smoking, check the float level is about right too, the favourite mistake is adding a fibre washer to the needle and seat assembly, that raises the level by quite a lot.
Also ignition timing and the advance retard mechanism can give you this type of problem too, if it is worn or sticking.
An Ngk B6 is fine, if you use it hard a 7 might be better but there isn't much in it. If it is an NGK BP6 or 7, they have an extended electrode and may be what you have heard about touching the piston. So check for a 'P' in the code. If it has an 'R' in the code it has a resistor in the plug and that isn't needed here and could (only possibly) add problems later. Hope this helps,

Steve.
Using yesterdays technology to create tomorrows problems today

Posts: 24
Joined: Mon Apr 28, 2008 11:44 am
Location: ESSEX UK

poor running / tickover G2

Postby paul miles » Sat Jun 07, 2008 11:39 am

Hi everyone
Thanks for all your help, the plug thing worries me a bit, a friend suggests putting a small piece of blue tac on the end of the electrode and turning the engine over by hand, if contact is made, it will/may show up on the blue tac, but thanks for all your advice it is much appreciated
Regards
Paul M

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poor running / tickover G2

Postby Biscuit » Sat Jun 07, 2008 2:33 pm

Agree with you Steve on the fibre washer under the float valve housing, but the new copies come with a washer at this point. Be interesting to find out whether the dimensions allow for this or the manufacturers have made the mistake.




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