Author Topic: B31 new owner - trouble starting  (Read 214 times)

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Calum

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B31 new owner - trouble starting
« on: 18 October, 2020, 19:14:40 »
Now I know what you're all thinking... another newbie who doesn't know how to start his bike, but please hear me out!

I've recently acquired a 1953 B31, which is complete and running and I have seen it so. I have also started it myself a few times, but it was pretty difficult and now cannot seem to get a spark at all.

Bike has been sat for a few months under a cover outside before I bought it, petrol in the tank was a bit stale but still fired up okay on viewing (took him a few goes mind, to be expected I suppose) and I have ran it a few times since then too. I have since filled the tank up with fresh petrol (though admittedly did not drain out the old stuff that was still in there, around a third of a tank perhaps).

I struggled to start it the other day, but once it was running and warm enough I could start it again no problem.

Ignition timing might be a bit out - move the advance/retard lever towards retard and it cuts out at idle (taught wire advance). There was a lot of slack in this at first so I've eliminated the backlash in the cable. Currently waiting on delivery of a timing disc and TDC tool to double check the timing (in the meantime I'll also buy or make a mag sprocket puller as I'm bound to need one eventually).

So after failing to start it today I checked through everything I could think of. Plenty of fuel getting in. Removed the plug, cleaned it up and gapped it to the book figure of 0.018" (gap was much larger). Plug looks very recent, Champion N83C I think it was (L10S equivalent is an N86C I think?) Checked the magneto points which were a bit close. Cleaned them with a bit of emery and opened them up to 0.012" (as per the service sheets).

I then tried kicking it over with the plug held against the engine. I probably got a spark once every 10 kicks or so... but not consistently either - sometimes 3 or 4 in a row and then nothing at all. I removed and checked the brushes on the pickup and on the earth brush too. Seems to be plenty of life in them both so I cleaned with electrical cleaner and refitted.

The carb is new and probably wants fine tuning (which I am fine about), the fuel might be a bit stale and the timing might be out but of course none of these would have an effect on the fact I cannot seem to get a decent spark kicking it over.

All I can think is it must be the mag (MO1), is it worth just taking the plunge and having it reconditioned? If so, recommendations for a firm to do a decent job most welcome. I'm not adverse to having it overhauled as I don't want to have problems with it in future and would like complete faith in it to be honest.

Any tips gratefully received!

idie

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Re: B31 new owner - trouble starting
« Reply #1 on: 18 October, 2020, 20:00:50 »
I see that the plug that you using is a copper cored one. This will be a late type plug with no glazing on the porcelain. These can get soaked with petrol and short to earth. Try and find an old style plug like an L10. This might well be your problem. Worth a try changing a plug.

Calum

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Re: B31 new owner - trouble starting
« Reply #2 on: 18 October, 2020, 20:31:48 »
Thank you, that's a very good shout and I'll get it swapped!
I did look for an L10S but couldn't see any in stock anywhere. I usually use the Green Spark Plug Co. but even they don't seem to have any. I'll have a rummage through my tin for something that looks vaguely suitable (and glazed porcelain around the tip) and have another go.

idie

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Re: B31 new owner - trouble starting
« Reply #3 on: 18 October, 2020, 21:18:56 »
If it is just to start the bike any old short reach plug will do. The values only really come in to being once up to temperature.

EDDIE SIMPSON

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Re: B31 new owner - trouble starting
« Reply #4 on: 19 October, 2020, 00:46:01 »
if its a magneto the first place i would look after checking points is the pick up holder for corrosion. also wipe clean the slip ring with the points plate removed.

EDDIE SIMPSON

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Re: B31 new owner - trouble starting
« Reply #5 on: 19 October, 2020, 00:53:13 »
sorry re read your post. but did you check continuity with a meter on the pick up? whats the condition of the pick up holder and carbon brush.

Calum

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Re: B31 new owner - trouble starting
« Reply #6 on: 19 October, 2020, 07:30:35 »
If it is just to start the bike any old short reach plug will do. The values only really come in to being once up to temperature.

Yes indeed, but it's mainly long reach plugs I seem to have 'in stock'. I'll have a look after work today.

if its a magneto the first place i would look after checking points is the pick up holder for corrosion. also wipe clean the slip ring with the points plate removed.
By this I assume you mean the connections inside the plastic pickup holder? The HT lead acorn nut connection seemed fine, and the pickup brush moved freely and seemed to have plenty of life left (maybe a good 5/16" or so of length before the spring). I didn't check for continuity I must admit but all looked good (although I know these can be mutually exclusive events!). If you mean the slip ring behind the pickup holder then I tried to give it a wipe whilst slowly kicking the engine over but it didn't look too dirty to start with. A bit awkward for access with the oil tank fitted.

Calum

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Re: B31 new owner - trouble starting
« Reply #7 on: 19 October, 2020, 19:13:31 »
I see that the plug that you using is a copper cored one. This will be a late type plug with no glazing on the porcelain. These can get soaked with petrol and short to earth. Try and find an old style plug like an L10. This might well be your problem. Worth a try changing a plug.

Well first thing after work I went straight to the workshop and dug around in my ice cream tub full of random plugs(!) and I found an old KLG F50. It actually looks as though it has never been used. Was already gapped at 0.018" so I tried it held on the timing case - nice consistent spark. Bike fired up second kick so at least it wasn't my technique, though I had obviously over-thought the situation and completely ignored the basics. Mind you the Champion plug looked okay and I didn't expect the shorting as you described - every day is a school day!
Thank you!

I started it several times and it was much easier than it has been previously. Now whether this is solely due to the plug itself or the points being adjusted who knows but I'm much happier with it already. The ignition can now be retarded quite a bit more as well to slow the idle down to a steady tick over. More tinkering and it'll only (hopefully) get better.

Thanks again.

idie

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Re: B31 new owner - trouble starting
« Reply #8 on: 19 October, 2020, 20:34:31 »
Glad it worked. The problem with our old clunkers is that we usually flood the carb to start, if it doesn't fire first time the excess fuel soaks into the unglazed porcelain then shorts the spark to earth.

TTJOHN

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Re: B31 new owner - trouble starting
« Reply #9 on: 22 October, 2020, 09:39:00 »
Also while on the subject of spark plugs, don't use a suppressed plug on a magneto.

TTJohn