The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => A7 & A10 Engine => Topic started by: mickpip on 27.07. 2014 10:15
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Hi All,
Just completed the restoration of my A10 and it fires up and runs well in neutral, however took it round the block and it sounded as though the engine was knocking under acceleration. Having renewed all the internal bushes and bearings including a crank re-grind, new con rods, re-lined bores etc etc I assume it is something to do with timing or mixture.
If anyone can assist I'd be extremely grateful.
Mike
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If you have fitted a choke, get the bike to wfo then close down the choke, very slowly.
If it gets better then you are slightly lean, if you start to 8 stroke then you are ok
now for the timing.
The cheats way to verify your timing is to adjust the points gap.
Down to .010" then up to .014"
Larger point gap causes the points to open earlier in the cycle ( advanced )
Smaller gap causes the spark to occur latter in the cycle (retarded )
So if opening the gap ( advancing the spark ) makes it better then your timing is too far retarded.
And visa versa.
Back in the day it was fairly common ( in my circle at least ) to do his if you were having troubles getting the timing spot on.
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Have you got somebody else to listen to it as well. A second opinion might help. If it's happening under acceleration I'm inclined to think it's pinking but I wouldn't describe that as a knock, more of a rattle.
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If it's happening under acceleration I'm inclined to think it's pinking
My first thought also, and it can sound like a knock (possible depends on compression used and maybe worse with an alloy head?), in my case both those counted and it was a fearsome sound, I can quite understand how it can wreck an engine.
Turned out to be ignition in my case, it was cured when I fitted Pazon unit, that's not to say it was a magneto at fault obviously, but maybe the Pazon has better control of advance retard or maybe it's just easier to set up correctly.
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Mike,
It's always great to hear of a completed restoration. Congrats. Also, welcome to the forum. If you get a chance, a few photos of your bike and a bit about how you came to be an "A"ppreciator are always interesting.
Regarding "knocking", we are all assuming you mean of the ignition type. If it is, indeed, ignition knocking you mean, maybe the problem is fuel octane. You haven't mentioned what pistons you have. Regardless, if you are not using premium fuel and, maybe, a lead substitute, you should give that a try (in addition to heeding the good advice given about timing).
Richard L.
Edit: Well, I see you did say "timing or mixture", so, equating to ignition "knocking". Sorry for my confusion.