Author Topic: start and idle on 1 cylinder  (Read 1447 times)

Offline madsens

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start and idle on 1 cylinder
« on: 09.05. 2010 08:34 »
Hi
My 1962 a10 starts easy enough, but only on the timing side cylinder, until I turn up the revs, then the other side kicks in as well. 
When I back of the revs again it starts missing on the primary side cylinder - The problem seems to disappear when getting hot. Is this the symptoms of the magic A10 Bias problem?  I've been looking around on the forum, and did find a few topics on bias, and anti bias gaskets, but am not quite sure if this is what im dealing with here?

I've just got a totally reconditioned mag installed (reconditioned by Theodole, NL) after my old mag gave up in the middle of overtaking a nice cruising Triumph Spitfire sportscar - a bit scary, just a few backfires and then like somebody just turned of the sparks - I just got around him and then had time to start breathing again.

regards
Joergen
BSA A10GF 1962
Denmark

Offline MG

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Re: start and idle on 1 cylinder
« Reply #1 on: 09.05. 2010 08:40 »
Hello Joergen!

What spark plugs are you using?
Try setting the spark plug electrode gap to 0.4-0.5mm, the 0.8 they usually have are too wide for use with our mags.
I don't think that's a bias problem.

Cheers, Markus
1955 A7 Shooting Star
1956 A10 Golden Flash
1961 Matchless G12 CSR

www.histo-tech.at - Restoration, Repairs, Racing

Austria

Offline roadrocket

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Re: start and idle on 1 cylinder
« Reply #2 on: 09.05. 2010 09:37 »
Hello Jørgen

I had the same problem last year, and it turned out that my HT connections were bad. Check all the way from the magneto to the plugs; maybe the connection in the pickup where the cable is fastened is not the best. Try running it in a dark spot, maybe you'll se sparks flying from the pickup to the magneto housing, because this is now the easiest way for the sparks. You need to make the way to the plugs the easist way for the spark to travel.

Otto in Svendborg (also Fyn!)
Otto in Denmark

G/F DAVE

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Re: start and idle on 1 cylinder
« Reply #3 on: 09.05. 2010 09:48 »
I Would try a plug swap first then if same try swapping leads over.If no joy then check pickups/brushes some replacement brushes are made from a harder type of carbon and can give problems as you describe. Definately sounds like a ignition problem. Dave.

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Re: start and idle on 1 cylinder
« Reply #4 on: 09.05. 2010 09:51 »
Also clean the magneto slip ring.

Offline olev

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Re: start and idle on 1 cylinder
« Reply #5 on: 09.05. 2010 10:41 »
Gday Joergen,
Have you done a compression test to see if both pots are the same?
I had a triumph spitfire years ago.
You could have passed that one on a pushbike.
cheers

Offline madsens

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Re: start and idle on 1 cylinder
« Reply #6 on: 09.05. 2010 14:13 »
Hi all

Thanks for all the good suggestions - I'll start checking them all in the morning - just came home from a short run on the bike - and everything i well and running good as soon as the handle is away from idle - but anyhow I guess they weren't really made to idling - but for driving  *smiley4*
Will see what the testing and trying tomorrow reveals!

Joergen
BSA A10GF 1962
Denmark

Offline madsens

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Re: start and idle on 1 cylinder
« Reply #7 on: 26.05. 2010 19:31 »
Sorry guys - a bit late in trying all your good suggestions !

But as a seaman i had to spend a fortnight at sea  (I work on a passenger ship sailing between Vopenhagen, Denamrk and Oslo, Norway. The firm says "no work no money" - I guess thats fair enough....

Anyway - I've tried swapping the two ignition sides from magnet to sparkplug, but primary side is still missing at idle. - I've put new ignition cables on both sides, so both plug caps, cables and pickups are new - and a totally renovated magnet.

I've taken the carburettor apart (amal concentric mark1 928) and cleaned everything out and blown through all holes and assembled everything, started up again, but same again ! The only advise from you I haven't tried is to check compression on both sides - guess that will be next - but keeping a fast idle keeps me enjoying the bike as the problem goes away when fast idling and hot..... any more suggestions out there?

Joergen
BSA A10GF 1962
Denmark

Offline MG

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Re: start and idle on 1 cylinder
« Reply #8 on: 26.05. 2010 19:49 »
Have you also tried cleaning the mag slip ring, like TT has suggested?

When the carbon dust off the brushes forms a conducting track around the slip ring, the spark will jump over to the cylinder that is not in compression stroke.

Just take one pickup out, earth the mag cutout, press a piece of cloth on the slip ring through the opening for the pick up and turn the engine/mag over with the kickstart (removing the plugs helps there).
1955 A7 Shooting Star
1956 A10 Golden Flash
1961 Matchless G12 CSR

www.histo-tech.at - Restoration, Repairs, Racing

Austria

Offline madsens

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Re: start and idle on 1 cylinder
« Reply #9 on: 04.07. 2010 15:06 »
Long time ago I started this topic - and in between I've been working on my ship a couple of periods, so its time to continue/round of....
After trying out all the good ideas and tips from you all, my mechanics got the problems pretty well located, mixed problems with mag and amal...
As I said earlier I just had a reconditioned mag put on, but there still seemed to be a problem with sparks, so he swapped mag - and it also turned out that the carb had developed a hair thin crack along the casting seam on the side, along with excessive wear in the slide, allowing lots of false air, so a new concentric went on as well. We also ended up with a bigger main jet.
So at the moment my A10 is a 1 kicker (mostly)  *smiley4* and she's got a lot more pull as well. Regarding the start and idle on 1 cyl. there is still a bit at cold start, but after a short while fast idling everything settles down to a steady idle - but strange enough it seems to miss a heartbeat once in a while, when idling - is that something any of you are familiar with.
But at the moment I am very optimistic and looking foreward to the BSA summercamp in Kent this month.

regard
Joergen
BSA A10GF 1962
Denmark