Starting problems when warm

Information relating to the Matchless G11 or AJS Model 30 600cc twin
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Starting problems when warm

Postby lasse » Fri Jan 17, 2020 2:52 pm

Hi all.I am new on this forum.I have a AJS 30 CS from -58.He start quite easy when cold,but I kick my knee out of funktion when he is hot or warm.I have tested the magneto in my own test,it gives sparks 6 mm long when cold.I have seen somewhere.that it is more difficult to get a spark under compression.What is the problem?

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Re: Starting problems when warm

Postby dave16mct » Fri Jan 17, 2020 3:49 pm

The most likely cause is the condensor in the magneto has broken down. You can fit a Brightspark 'Easycap' condensor on the points plate but the old one needs to be disconnected and its buried in the end of the armature. Google Brightspark Magnetos to see the details.
Dave.

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Re: Starting problems when warm

Postby Ralph » Fri Jan 17, 2020 3:57 pm

Have you tried the spark when it's hot?
when electrics start to fail they very often
fail when hot but will work once cooled
down, I would suspect the condenser.

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Re: Starting problems when warm

Postby bitza » Fri Jan 17, 2020 5:19 pm

Magneto first to check, quite common fault with age.

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Re: Starting problems when warm

Postby Duncan » Fri Jan 17, 2020 9:36 pm

Sounds like a magneto/condenser issue but check some other simple things first like:
Do you have an insulating spacer between the carburettor and inlet manifold?
Is the engine running lean/is there an air leak on the manifold?
Are you valves/tappets correctly adjusted?
Are the HT leads in good condition and the spark plugs and plug cap?
Have you owned the bike for long, has it always been like this?

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Re: Starting problems when warm

Postby MalcW » Mon Jan 20, 2020 9:31 am

My G12 has had a full magneto rebuild but is still harder to start when hot. But genuine Champion spark plugs, and giving it a swift kick withOUT retarding the ignition have helped a lot.

Malc

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Re: Starting problems when warm

Postby clive » Mon Jan 20, 2020 12:43 pm

dave16mct wrote:The most likely cause is the condensor in the magneto has broken down. You can fit a Brightspark 'Easycap' condensor on the points plate but the old one needs to be disconnected and its buried in the end of the armature. Google Brightspark Magnetos to see the details.
Dave.


I agree with this, had to do it on a rebuilt mag after about 6 months of use which came with my 1958 G11CS. I was lucky and the "condensectomy" as described on the website was easy to do. I bought two Bright Spark units keeping one as a spare taped in the headlight in case the first gave up the ghost. Never got it out in the last 5 years except to show people what the Bright spark unit was like!
clive
if it ain't broke don't fix

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