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Messages - Foghorn

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British Bikes / Re: 1951 B31 Plunger BSA Carburetter
« on: November 30, 2016, 10:36:17 AM »
I like the suggestion about the tappet clearances- haven't checked them.  Spark plug too.
The car behind is a 1939 Flying Standard 12.  Must finish it off too!  The rear gearbox seal seems to be non-existent.
How does one test a magneto apart from option one?  [Option one- hold the spark plug lead while your 'friend' kicks the engine over].
Foghorn.

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British Bikes / Re: 1951 B31 Plunger BSA Carburetter
« on: November 30, 2016, 12:11:13 AM »
Yeah!  The magneto was totally rebuilt.  One assumes the job was done well and at this time I have no reason (well, not until I opened today's forum replies) to think otherwise, but I will pursue the thought.  The magneto and the bike has only 15 miles on it since rebuild and most of those were put on by the bloke who did the roadworthy certificate.
Yes R, I had 3 years of fun- now the fun starts.  I will see if I can attach a pikky.
Burlen, JFerg, for a mono or concentric as suggested by Rex.  Thank you all.
Initially at the first ride, the bike seemed to work without stopping- [it actually started FIRST kick].  There was just a faltering, an inconsistency of operation which made me look at the carby.  It was after the replacement of the throttle slide and the required honing of the tunnel mouth to fit same (see my reply post to another member) that the symptoms altered for the worse.  It seems that the worn slide worked better than the new one.  Now with the old slide back it place perhaps it may be a little over-honed, but a new carby is sounding better and netter.
Foghorn.

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British Bikes / Re: BSA 1955 B31
« on: November 28, 2016, 09:21:53 PM »
Re my carby post- I have been fiddling with the carby on my 1951 B31.  I did find an odd thing or two:
After removing the jet block (by tapping it down out the bottom of the slide tunnel, I found very slight deformations at the point where the vertical slots in which the throttle slide runs, and this was causing the slide to catch at that point.  I used a 3 square scraper to gently remove the high spots found there.  The throttle slide slipped freely through the entire length of the slide tunnel then, and also freely over the jet block.
When I re-inserted the jet block and then slid the throttle slide down into the slide tunnel, it slipped nicely over the jet block as it should.
However, when I tightened the large nut over the bottom of the jet block, a distortion occurred so as to cause the throttle slide to jam when it was well down over the jet block.  By loosening the nut slightly the jammed slide was freed.  I think the carby body was being distorted ever so slightly.  So-
How tight should the nut be?
My carby is well used/worn. The carb had been dropped on the top of the slide tunnel as some time and there was a tight spot just at the top thread area so that the slide was tight until it cleared the very top edge of the tunnel (it didn't affect the slide through its operating range though).  When I tried to fit a new throttle slide I found I had to hone the tunnel bore to get it to fit, and even then It was sticky.  Eventually I went back to the original slide and I think that is why in my own post I am after a new carb.
I hope my story helps.
Foghrn.

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British Bikes / 1951 B31 Plunger BSA Carburetter
« on: November 28, 2016, 08:56:57 PM »
Hello all,
My B31 is now restored and running.  But the carby is rather worn in the slide tunnel, which may not be the only fault with it.  The symptoms are that, though the bike starts first kick and runs nicely, after some 2 miles or so the fully re-built engine loses power, farts a little and then just sighs to a halt.  Judicious tweaking of the throttle may keep it going but without substance and it dies.  It is an AMAL 275 separate float chamber model.  I have not been able to find a new replacement for it.  I wondered if someone can tell me if there is a later AMAL model carby which could be pressed into service in lieu.  An AMAL monoblock would be satisfactory, but I do not want to spend money on what will really be a trial without some re-assurance that it will essentially be the same carburooster.
Regards, Foghorn.

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