Im Stumped!!

Information relating to the Matchless G9 or AJS Model 20 500cc twin
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NZMatchless
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Joined: Sat Mar 16, 2019 8:48 pm
Location: Essex UK

Im Stumped!!

Post by NZMatchless »

When I first fire up my 53 G9, she always starts up on the left cylinder only, it eventually fires on both cylinders after about 20 secs, I've tried swapping plugs and leads but still the same, once it's warm it's fine and stars up on both cylinders straight away, The Magneto has been refurbished and I have a new Amal Carb I'm stumped![img]64736343_10156820880127912_7926927633047093248_n.jpg[/img]
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Mick D
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Location: Aberdeenshire

Re: Im Stumped!!

Post by Mick D »

Hi

Have you checked the plugs for colour, indicating mixture strength? It sounds like your mixture could be a little on the lean side. Are your exhausts blued where they exit the head?

Regards Mick
Oggers
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Joined: Mon Jan 14, 2019 5:37 pm
Location: Aberdeenshire

Re: Im Stumped!!

Post by Oggers »

Tappets for that cylinder incorrectly set?
Weak valve springs?
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Rob Harknett
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Re: Im Stumped!!

Post by Rob Harknett »

Try a new recommended type plug instead of changing them round. There maybe a slight difference on the dodgy cylinder the old used plugs don't like
MalcW
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Location: DEVON UK

Re: Im Stumped!!

Post by MalcW »

Just out of interest, have you tried removing the RH plug before starting from cold, to see if it's actually sparking at that point? As has been pointed out, changing the plugs completely, rather than swapping, could be worth a try. I have recently fitted Champion N5C plugs (previously NGK B8ES) and it's made a big difference. Have you tried swapping the HT cable and plug caps from side to side?
Also, have you tried a compression test? If you don't have a compression tester immediately to hand, does the compression feel similar on both cylinders when kicking it over? It does have the feel of a mechanical issue rather than electrical - sticking valve or piston rings for example.

Malc
Winkie
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Joined: Sat Nov 26, 2005 10:47 pm
Location: WEST MIDLANDS UK

Re: Im Stumped!!

Post by Winkie »

When my model 31 was rebuilt it did the same, except that it was the right hand cylinder that fired up, with the left taking its time, if at all. The magneto was newly rebuilt and the plugs were new NGKs. In the end I cured it by sticking in a set of Champion plugs, non insulated of course. Instant result. The magneto just did not like NGKs!
MalcW
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Re: Im Stumped!!

Post by MalcW »

Winkie wrote:When my model 31 was rebuilt it did the same, except that it was the right hand cylinder that fired up, with the left taking its time, if at all. The magneto was newly rebuilt and the plugs were new NGKs. In the end I cured it by sticking in a set of Champion plugs, non insulated of course. Instant result. The magneto just did not like NGKs!
Exactly the same as me! I got Champion N5Cs from The Green Spark Company and it's like a different bike!

Malc
SPRIDDLER
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Re: Im Stumped!!

Post by SPRIDDLER »

There are said to be fake NGK plugs around.
It might be worth checking yours:
NGK fake plugs (640x398).jpg
More on the NGK website:
http://www.ngk-sparkplugs.jp/english/te ... index.html
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NZMatchless
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Location: Essex UK

Re: Im Stumped!!

Post by NZMatchless »

Mick D wrote:Hi

Have you checked the plugs for colour, indicating mixture strength? It sounds like your mixture could be a little on the lean side. Are your exhausts blued where they exit the head?

Regards Mick
Ride New Zealand - Live the Dream
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NZMatchless
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Joined: Sat Mar 16, 2019 8:48 pm
Location: Essex UK

Re: Im Stumped!!

Post by NZMatchless »

Mick D wrote:Hi

Have you checked the plugs for colour, indicating mixture strength? It sounds like your mixture could be a little on the lean side. Are your exhausts blued where they exit the head?

Regards Mick

Mixtures fine plugs are a light brown and no blueing on the pipes
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