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Model 18 magneto ?

Submitted by colin_mccabe on Mon, 13/06/2016
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Singles

Hello.

I seem to be having a few magneto related issues.

My 1951 model 18 is very sporadic starting and runs poorly at low rpm and back fires a lot on over run. It is running a later concentric carb.

I have set the timing as best I can at 5/8 btdc although the magneto plate appears to have a keyway which prevents much movement either way.

Do we have a concensus of opinion as to who is the best place to send my magneto to have it checked out?

Thanks.

Colin.

Submitted by george_phillips on Tue, 14/06/2016

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Poor slow running and backfiring on overrun could indicate a weak pilot mixture, Colin. Or a loose exhaust pipe retaining collar? George

Submitted by robert_tuck on Tue, 14/06/2016

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I was convinced my mag was in need of an overhaul, and have no doubt a re-magnetise would be beneficial,however with carefull attention to all the other suspects I now have a bike that starts and runs reliably. I recommend you check , the plug gap is on the small side.no resistor in the plug or cap. mag points are clean and gapped ,earthing brush and track clean, Fit a new plug (not a cleaned one) unless you have a clean plug made before the mid 1970's !,get the mixture right so as to not soot the plug up. If the bike will start without a tickle thats good as some fuel additives get into the insulator and are not easy to clean off. Backfiring can be air leaks but also unburnt fuel in the silencer from poor ignition. Might be worth trying the dreaded ethanol fuel as some bikes don't like the additives in top grade fuel.

Submitted by colin_mccabe on Thu, 16/06/2016

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Thanks for the replies.

I will try and adjust the pilot mixture some more, i have adjusted this previously but it seems to make no real improvement to the low speed running. I know the main jet is a bit large but I'm not sure about the pilot jet.

what plug model would you recommend?

Colin.

Submitted by robert_tuck on Thu, 16/06/2016

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I can't advise on the plug grade but a very old plug (pre 1975 ) is likely to work a lot longer than anything current and will respond to cleaning (not with a steel wire brush!).

Submitted by andy_marks on Fri, 17/06/2016

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Hi Colin

I run my '51 ES2 on a Champion N4C with no trouble.

You're problems sound more like carburation to me. You say its a later concentric but what sort of condition is it in? If the slide and/or body are worn this can cause havoc with running at lower speeds. Needle and needle jet wear can mess up carburation as well.

How are you setting your timing? You should be setting it by putting the sprocket on the taper with the engine at 5/8 BTDC and the magneto fully advanced.

Good luck

Andy

 


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