The AMC God giveth...

Helpful information and requests for assitance and advice
MalcW
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The AMC God giveth...

Post by MalcW »

...and the AMC God taketh away.

This weekend, After extended fettling of my non running Model 31 - cleaning out a messy tank, cleaning the carb out, freeing up a stuck clutch, and sending of the magneto for an extended rebuild, oil change etc., I got her started - more to my surprise than anyone else's. just for a few seconds, A second start ensued, for much longer, and she sounded good. But she would not run on anything other than full choke. Eventually, after a minute or so of fiddling and trying the choke again, she cut out, and wouldn't restart. I checked the magneto points were still OK, removed, cleaned and gapped the plugs (they were slightly wide), and tried again. Still no joy. And then the kickstart return spring came adrift; or broke, I'm not sure which yet.

So, progress, but not the unbridled success it could have been.

I've already ordered a new spring, but would like people's thoughts on the carburettor. Someone has fitted a Mk1 Concentric in the past, and I'm suspecting either a warped flange giving an air leak, or problem with the pilot jet. What do you think? Or should I just fit a new Monobloc?

Thanks,

Malc
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Rob Harknett
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Re: The AMC God giveth...

Post by Rob Harknett »

You could try a new plug. Plugs are not meant to be cleaned. Cleaning will cause damage. Old plugs used to have glazed central electrode insulator. They have not been glazed since the 70's. If you have sumped oil, it may need draining, otherwise the plug will soon get oiled up.
Mick D
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Re: The AMC God giveth...

Post by Mick D »

Hi

Assuming you have confirmed you have a spark:

My first port of call would be to strip the carb and ensure the jets, filter, galleries etc. are clear and flange is flat. - you don't need much in the way of debris to cause the effect you have and considering the bike has been dormant for a long time it's a probability. Re-assemble with new seals and gaskets and try again. This will also give you a chance to assess the condition of the carb throttle slide / bore etc.

I'm a purist so would go for a new Monobloc if the Concentric proves faulty.

Regards Mick
56G80S
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Re: The AMC God giveth...

Post by 56G80S »

Rob

"Plugs are not meant to be cleaned." If I didn't I would be a poor man. I've had success cleaning with an old stiff toothbrush and meths. This is what I did with the one photographed in my other thread at present "Top speed reduced".

Same plug got me to the Alternative and back last year after this treatment.

But you are quite right - they won't stand the old brass brush.

Johnny B
SPRIDDLER
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Re: The AMC God giveth...

Post by SPRIDDLER »

Yep, as MickD said, sounds like gummed up jets or debris, especially the pilot jet and the very fine galleries in the body of the carb. I make no apology for repeating that th'engine is fed primarily with fuel from the pilot jet at the smaller throttle openings so having to use the choke to get it running seems to confirm a blockage. Old ethanol petrol in the carb/filters turns to treacle.
There's an excellent tuning guide for the Concentric here:

http://www.hitchcocksmotorcycles.com/pi ... ettors.pdf

I too would fit a Monobloc if a good clean of your Concentric doesn't help. They're dearer than the Concentric but they just look 'right'.
56G80S wrote: I've had success cleaning with an old stiff toothbrush and meths.
I guess the nylon bristles of a toothbrush are o.k. It's fine for you whippersnappers but we more mature fettlers find leaving the plug to soak overnight in Steradent with the dentures works well ;)
'There is a tide in the affairs of men
Which taken at the flood............'
MalcW
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Re: The AMC God giveth...

Post by MalcW »

Hi All

I just used a piece of fine emery folded over to ensure the electrode and earth were clean,followed by a quick puff of air to blow any dust away. I must admit I'm leaning towards a Monobloc at the moment - I've always preferred them anyway, but in the interests of my wallet I'll check the Concentric over first.

I got my new kickstart spring this morning. Can anyone confirm where the gearbox drain is? I seen to have 1 bolt underneath at the front, and 2 at the back. Or I can just take the outer cover off and then clean up the mess!
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Rob Harknett
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Re: The AMC God giveth...

Post by Rob Harknett »

After my bikes have been standing I need to drain some oil and I clean the plug. The bike will start OK just to run the engine a while. Same procedure next time, as the plug soon gets contaminated. I do expect to keep doing this, or replace the plug. If the bike in question is not one I regularly use. I don't bother changing the plug. As the bike is not going anywhere.
PS no one has ever mentioned an old tip about plugs. ( another tip passed on to me by the "old boy " over 60 years ago )
We cleaned plugs then, also told. Using a soft lead pencil draw on the electrodes. This will leave a deposit of lead on them. Do that boy and your bike will start first kick, I was told.
You should see quite easily the correct bolt to drain the oil, it should also have a sealing washer which should be visible before you completely remove the bolt. Good idea to always replace that with a new fibre washer. At least make sure gearbox, bolt and washer are clean.
SPRIDDLER
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Re: The AMC God giveth...

Post by SPRIDDLER »

MalcW wrote: Can anyone confirm where the gearbox drain is?
Don't you have the Workshop manual, Owners Manual and Spares List? They can be viewed and downloaded from Christians Archive.
http://archives.jampot.dk/book/

The drain plug is Part 15 in the illustration .......
http://archives.jampot.dk/technical/Tra ... d_view.pdf
Don't remove the Detent spring and plunger bolt part 20 in the illustration!!(But if you do by mistake then do not move the gearchange lever).

I'm sure there are better illustrations in the Archive but you can search for them ;)
Have a look in the 'Transmission' section where there are also strip/rebuild instructions.....

http://archives.jampot.dk/technical/Transmission/AMC/
'There is a tide in the affairs of men
Which taken at the flood............'
raffles
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Re: The AMC God giveth...

Post by raffles »

Go for the monobloc buy it from club spares with your spares discount it is the best buy around
Tony
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Expat
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Re: The AMC God giveth...

Post by Expat »

raffles wrote:Go for the monobloc buy it from club spares with your spares discount it is the best buy around
Tony
Agree, Agree, Agree. :P
Keep shiny side up.

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