Author Topic: Magneto issues?  (Read 3118 times)

Offline BSA500

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Magneto issues?
« on: 20.03. 2013 13:10 »
Hi,
I think by posting this I may be answering my own question. For quite a while the A7ss has had an annoying misfire/stutter when accelerating from approx 1/4 throttle upwards. I had put this down to a horrible worn slide-so worn it ticked and you could hear it over the engine. I replaced the carb with a spare which was the smaller 15/16 but had a resleeved body. The bike now ticked over and actually ran rich due to less air going around the old slide. Anyhows the annoying stutter/missing is still there. I experimented with different needle jets as the old one was a 107 but no improvement. Is there anything easy to try on the mag to check it out. Some other things I have done....
New plugs,new leads,no caps just direct wired to the plugs(rain does not effect them). I suspect its a rebuild/check over but it starts first kick, nice tick over-oh its better when the engine is cold( i know suggests mag as when its warmer its worse).
I do 26 miles a day every day so its not standing around. I f it needs a check/build it will go to Priory mags.BTW the dynamo he rebuilt for me is going great no issues all winter *smile*

Offline muskrat

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Re: Magneto issues?
« Reply #1 on: 20.03. 2013 18:40 »
 G'day BSA500, better when cold means it's rich and the stutter could be your slide cutaway or pilot jet (it affects the whole range not just idle).
I can't comment on the magie, I went lectric 20 years ago.
Cheers
'51 A7 plunger, '57 A7SS now A10CR,  '83 CB1100F, 88 FXST .
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Online Angus

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Re: Magneto issues?
« Reply #2 on: 20.03. 2013 19:52 »
When my A7 was first brought back it had a misfire/stutter at about that point. Roger came and took it back. Fitted a larger carb (its to SS spec inside) and rejeted also dealt with induction bias
1961 A7 since 1976
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Offline BSA500

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Re: Magneto issues?
« Reply #3 on: 20.03. 2013 20:06 »
I suppose I should rebuild the 1 inch carb first then. problem is it needs resleeving which then means you cannot try out different slides. I know I could buy a new carb but its only £50 against £150. Strange the stutter did not change when I swopped carbs I could try a smaller pilot as well at the moment I am using a 30 pilot.

Offline A10Boy

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Re: Magneto issues?
« Reply #4 on: 21.03. 2013 13:07 »
Have you clean the slip ring, set the points, replaced pick-ups etc? To me, if it's still doing it with a different carb fitted, it would be a mag issue.

Regards

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Andy

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Offline BSA500

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Re: Magneto issues?
« Reply #5 on: 21.03. 2013 19:47 »
i will do the magneto checks but I did swop over the jets from one carb to another,so in theroy the same issues have been transferred over. The only differences being the smaller choke size 15/16 instead of 1 inch and a good fitting slide(resleeved). The biggest improvement was that now I have a tickover and she does not spitback or try to die when opening the throttle off idle. I think other than a quick check over of the mag would be to get the 1 inch carb resleeved and jetted according to the specs and go from there.

Offline Topdad

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Re: Magneto issues?
« Reply #6 on: 22.03. 2013 11:11 »
Always worth doing the standard stuff on the mag set it up ok then get the carb done ,sorry you're so far away I'd lend you my carb .Last time I rode to kent (1966 ) took me 14 hours . Anyone closer to help? best wishes Bob .
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Offline BSA500

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Re: Magneto issues?
« Reply #7 on: 22.03. 2013 11:52 »
Thanks for the offer. 14 hours blimey that is dedicated riding. Where abouts in Kent?

Offline Topdad

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Re: Magneto issues?
« Reply #8 on: 22.03. 2013 12:40 »
It was the last family holiday in 1966 ,my dear old mum and dad ( he being a true born cockney ) always took us to Ramsgate for our hols when we lived in Manchester ,we moved to liverpool and decided it would be nice to go again once more so I follwed him in there camper so quiet slow 45 max however the rain was of biblical proportions ,I had to be rescued by the firebrigade under a bridge in rudgley stone  mag was under water !!  ..kaput  but pulled it out dried it off used that new fangled (then )wd40 stuff  and bingo on our way again ,boy did I sleep when we got there!! strangely looking back I was rather pleased with myself , (......sorry e here I go again wind wondering of topic ) Finally remember visiting Manston to see the spit and hurri ,they were still outside then and looking very sorry but to be able to get that close ,feels like yesterday and certainly worth the 14 hours best wishe and hope you sort your misfire BobH.
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Offline BSA_54A10

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Re: Magneto issues?
« Reply #9 on: 22.03. 2013 20:24 »
Spend £ 30 on a colour tune and stop wearing your brain cells out.
With it you can look at the combustion colours as you open the throttle .
If the flame goes out & you can see the spark then you have a carb problem.
If the flame goes white ( lean ) or yellow ( rich ) you have a carb problem ( note it should go rich momentarially as you open the throttle )
If the flame goes out and you can not see a spark, or the spark is not constant then you have an ignition problem.

Of all the "special tools" in my tool chest this one gets the biggest work out.
Knocks down tracking problems in 1/2 and just about every one who watches me using it ends up buying one.

Just two tricks to remember.
1) run the bike from a lawnmower fuel tank hanging on a stand so you do not run the engine stationary for too long
2) lightly engage the rear brake & pop the box into a high gear to put a bit off a load on the engine

Bike Beesa
Trevor
Bike Beesa
Trevor

Online bsa-bill

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Re: Magneto issues?
« Reply #10 on: 22.03. 2013 22:08 »
Quote
If the flame goes out and you can not see a spark, or the spark is not constant then you have an ignition problem

spot on Trevor

it did and I had, as yet I've not had time to find out why but suspect a series of duff plugs and maybe Magneto condenser - all on a to do list
Meanwhile Pazon performs with distinction
All the best - Bill
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1959 Rocket Gold Flash - blinged and tarted up  would have seizure if taken to  Tesco

Online Triton Thrasher

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Re: Magneto issues?
« Reply #11 on: 23.03. 2013 09:52 »

Just two tricks to remember.
1) run the bike from a lawnmower fuel tank hanging on a stand so you do not run the engine stationary for too long

I don't understand. Don't run it too long, by pressing the kill button.

Quote
2) lightly engage the rear brake & pop the box into a high gear to put a bit off a load on the engine


Be aware of what will happen if you knock the bike off the stand, or get something caught in the chain.

I have landed myself with two Colortunes, which is good on a twin. The odd thing is, an ideal coloured flame at idle doesn't always seem to be so ideal when you go out and ride around on the bike. I ended up setting the idle mixture, by ear, for best running at a teeny-weeny throttle opening, held by the cable adjuster. I know that's wrong, in theory.

Mixture at bigger throttle openings isn't hard to get right by road testing.

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Re: Magneto issues?
« Reply #12 on: 23.03. 2013 10:23 »
Quote
I have landed myself with two Colortunes,

Lucky lad, I can see why for once overspending would be a big benefit, I will continue to swap mine from one side to the other until someone comes up with a good price, unfortunately when I got mine Halfords didn't do a bogof
All the best - Bill
1961 Flash - stock, reliable, steady, fantastic for shopping
1959 Rocket Gold Flash - blinged and tarted up  would have seizure if taken to  Tesco

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Re: Magneto issues?
« Reply #13 on: 23.03. 2013 10:30 »
Quote
I have landed myself with two Colortunes,

Lucky lad, I can see why for once overspending would be a big benefit, I will continue to swap mine from one side to the other until someone comes up with a good price, unfortunately when I got mine Halfords didn't do a bogof

The second one was cheap second-hand.

Spitfiremk9

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Re: Magneto issues?
« Reply #14 on: 23.03. 2013 10:57 »
Thanks Triton thrasher, forgotten I had one tucked away in the garage must dust it down and use it, regards Bobh