The BSA A7-A10 Forum

Technical => Lucas, Electrical, Ignition => Topic started by: tommo903 on 10.06. 2017 22:43

Title: A7SS Starting Issues
Post by: tommo903 on 10.06. 2017 22:43
Hi all,
I'm hoping that someone can shed some light on a starting problem I'm having with my '55 A7SS. I've recently refitted my magneto after Andrew at Priory Magnetos refurbished it for me but I'm wondering if there's something about the timing I haven't got quite right.
I worked to the notes in the service sheets and even went to the trouble of buying one of those detectors that lights up just as the points are opening. When it lit, I checked the points gap at 0.002" (at full advance) so therefore, considered all should be ok. Refitted everything and was ready to start it. I set the ignition lever to the retarded position and with choke full on tried kicking it over. However, every time I kicked over the lever kicked back hard with a fair bit spitting, etc. I didn't start and worse still, after about the tenth kick, the lever snapped at the bottom near the pin so now I need another. Any thoughts on what I could have done wrong?
I bought this bike last August and have hardly ridden it yet and now feeling a tad cheesed off to say the least!  *sad2*

Thanks, Steve
Title: Re: A7SS Starting Issues
Post by: Billybream on 11.06. 2017 06:27
Hi Steve.
Never found the need to use choke during the UK summer, so suspect your mixture is way out.
Spitting back would normally indicate weak fuel to air mix.
0.002" points gap should be 0.012" at correct ignition timing position.
Title: Re: A7SS Starting Issues
Post by: Greybeard on 11.06. 2017 09:24
I recently made the schoolboy error of timing the wrong cylinder so I had to swap the plug leads around.
Title: Re: A7SS Starting Issues
Post by: JulianS on 11.06. 2017 10:13
Sounds like the timing is too far advanced.

Suggest you set it again as per the book - mag on fully advanced, points just opening, piston at the appropriate position before TDC (3/8 inch in my book), gently tap the pinion on and tighten the nut being careful that the mag does not move in relation to pinion which sometimes happens and mucks up the timing. With the mag timing light as soon as it comes on then that is the correct position with points just opening. If you turn the mag any further you will likely get too advanced. Then check timing and if it is still OK check timing on the other cylinder which should be close to the same figure.  With a Priory mag I would not expect much if any difference.

Fully open points gap should be 12 thou there may be a little variance between the 2 cams on the slip ring, though with a Priory mag again I would not expect much difference going by my experience of Andrews high standard of work.

You need a little slack on the ignition control cable so that the mag is not held off fully advance in the timing procedure.

The broken lever is a worry - not heard of this happening before on the A twins. Is it a new one - I would like to avoid getting one from the same source if it is.
Title: Re: A7SS Starting Issues
Post by: Greybeard on 11.06. 2017 11:24
Sorry to be pedantic but check points gap before the timing.
Title: Re: A7SS Starting Issues
Post by: raindodger on 12.06. 2017 19:10
Hello, Gents.
                 I was involved with a bad starting bike today.  OK, it wasn't a BSA but it was a pig to start.  The bike had coil ignition, but the spark was weak, checking it out I found a resister plug and a resister cap, changed the plug for non resister and it fired right up.  The owner was very pleased, and so was I.  This may be useful to someone.
Title: Re: A7SS Starting Issues
Post by: muskrat on 12.06. 2017 20:35
That's a good point raindodger, often overlooked. Non resistor plugs & caps are better for magneto ignition.
Title: Re: A7SS Starting Issues
Post by: tommo903 on 13.06. 2017 23:13
Thanks all, for the words of wisdom.
I will take your advice Julian and go back to the beginning and re-check the timing. I'd like to think that I did do everything you said, but obviously, something has not gone quite to plan. I can only think that the points must have moved a little when refitting the pinion. By the way, when I said the points were at 2 thou, I meant they were just opening and that's the point where I refitted the pinion, otherwise, they were 12 thou fully open.

Greybeard...I was starting to wonder if I'd set the timing to the wrong cylinder, but once I'd broken the kickstart, I didn't get the chance to do the 'swap over' test!

Breaking the kickstart was a bit concerning, it's never happened to me before and I certainly wasn't kicking particularly knees prevent me from doing that anyway! It was on the bike when I bought it so I'm assuming it was the original item, although it had been rechromed. I've bought another and just awaiting its arrival...I'm told is a genuine item.

I'll report back after doing a re-check.
Cheers, Steve
Title: Re: A7SS Starting Issues
Post by: trevinoz on 14.06. 2017 22:28
Did you not check the timing after you nipped up the pinion? Basic error.
Title: Re: A7SS Starting Issues
Post by: RichardL on 14.06. 2017 22:52

Tightening up the pinion without messing up the timing is tricky (for me, maybe not everyone). I try to sneak up on it. The first thing I do is use a socket and a light hammer tap to gently tamp the pinion onto the taper. Then, I use my thumb to hold a bit of back pressure at the points plate while finger tightening the pinion bolt. Then, I use the socket to tighten the bolt as much as I can hold back with a sore thumb. Then, I do the first recheck. If that's good, then the bolt gets a final tightening and the timing gets another recheck.

There WILL be better ideas and advice as to the best way to do this and I will read them carefully to see if I have already failed attempting them in the past.

Richard L.
Title: Re: A7SS Starting Issues
Post by: orabanda on 15.06. 2017 01:22
If you slot the mounting holes in the magneto mounting flange, you will be able to achieve approx 18 degrees of variance of the timing once the bike is running. Carefully tighten the nut when the magneto is in the middle point of the slot(s). Then you will be able to advance or retard timing 9 degrees.

Avoid heavy loading against the fibre gear when tightening the nut; this could lead to tooth failure down the track.
Title: Re: A7SS Starting Issues
Post by: Black Sheep on 15.06. 2017 06:46
The timing must be over-advanced. It is essential to re-check the timing after tightening the pinion. It's remarkable just how far it can be out once the pinion is tightened. Of course, you must check timing on both cylinders. It's not impossible for the cam ring to be amiss, though I would be surprised if that were to happen with a Priory rebuilt mag.
As for the broken kickstart. That really shouldn't be possible unless there is a serious flaw. I take it it's a pattern part. 
Title: Re: A7SS Starting Issues
Post by: Zander on 15.06. 2017 07:24
Slotting the magneto mount holes sounds an interesting and convenient option for tweaking the timing without the rigmarole currently involved.  I likes the sound of that! *smiley4*
Title: Re: A7SS Starting Issues
Post by: tommo903 on 15.06. 2017 09:34
Trev, yes, I do admit to committing the most basic of errors…lesson learnt.

Richard…thanks for that, what you have described was pretty much my concern before attempting this, i.e. how to prevent the points from moving. I was told that once the pinion was on the tapered shaft and meshed with the adjacent gear, that provided no movement had taken place up to that point, then all would be ok. Any subsequent points movement was nothing to worry about as the points and pinion were moving 'together'. Is this not correct? If not, then it's not surprising that the points setting could be well out!
Something else has occurred to me as well and I could be making an even more basic error here as well, due to my lack of understanding regarding the ignition control lever (never had to deal with one of these before). Prior to setting the position of the points where they just start to open (2 thou), I moved the lever into the fully advanced position but when I attempted to start the bike, I moved the lever back to the closed position, assuming that once started and I ride off, the lever would need reopening again to a position that felt 'right'. I would be interested to know how others use this lever when starting and riding, is it a case of 'feel' depending on speed, etc? I asked the previous owner how he used it and he said he never bothered touching it.


Title: Re: A7SS Starting Issues
Post by: JulianS on 15.06. 2017 09:52
For starting retard the ignition control a bit maybe 1/3 - the actual best position  for your bike will come to you as you use it. Wire goes tight when retarding.

With the engine running keep the lever fully advanced or  advanced as far as possible for conditions, you will feel if the engine needs a little retard on a hill or trickling through slow traffic. You will find the Shooting Star quite easy in this respect.

It will tick over better with a little retard.

I have had my A10 for over 40 years and it sometimes takes a couple of attempts to get the timing right.
Title: Re: A7SS Starting Issues
Post by: tommo903 on 15.06. 2017 10:38
Julian...thanks. Something you've said there, i.e. "wire goes tight when retarding" has made the penny drop! I'm certain I read it somewhere that tightening the cable advances the ignition and I've been working on that basis. However, from a search on this site, I now know that for a K2F mag, it's the other way round, although the opposite for some other types of magneto (another basic error I hear you say!). So my points 'set position' has been wrong anyway regardless of whether they moved or not when re-tightening.
Crikey, I'm definitely learning the hard way here!  *sad2*

Title: Re: A7SS Starting Issues
Post by: JulianS on 15.06. 2017 10:48
Sounds like you will be up and running very soon.

Good luck.
Title: Re: A7SS Starting Issues
Post by: tommo903 on 28.06. 2017 08:24
Pleased to report that having finally got round to resetting the timing with the A/R lever in the correct position, the bike started after 2-3 kicks and seemed to be ticking over quite nicely  *smile*, albeit just slightly on the high side. I'm hoping this will be nothing more than some time carb fettling with the pilot air and throttle stop screws which I can do prior to the weekend in time for a test ride.

I'll let you know how it goes. Thanks for all your help with this.