The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => Lucas, Ignition, Charging, Electrical => Topic started by: Neil_EngUK on 16.11. 2013 17:43
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I have a very relaible 1950 A10 Rigid, built up by Matthew and Margaret Mason, of Gannet Racing fame in the 1980s.
Earlier today (after a long/fast run) the bike started to suddenly backfire at high revs.
It is fine at low revs and ticks over like a clock.
I suspected ATU and was surprised to find there is no such device under the timing cover! (Only the magneto pinion, bolting onto the K2F magneto.) This is the first time I have ever had need to take this cover off, as the bike has been wonderfully reliable for over 30 years. It has never had a manual advance/retard.
Can anyone explain what is going on and how can i sort the backfire issue please?
Recently, the points were changed, but the timing/magneto/slipring have not been touched.
Also, can anyone put me in touch with Matthew or Margaret Mason? My mate was a customer of theirs in their Didcot Shop 'Masons', and he ordered the bike from them in the 1980s. I bought the bike off my mate 20 years later, after he stopped riding, following an accident.
Many thanks Neil
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G'day Neil, *welcome*.
That is very strange, both the no advance unit and not touched in 30 years.
A low comp motor will idle and run on a fixed advance (most 2 strokes are) OK but would go better with it adjustable.
Backfire at high revs could be a few things other than timing or magneto. Partially blocked main jet, sad or broken valve spring/s, spark plug.
How have you been checking and adjusting the timing?
Cheers
ps, give us an intro in Bikes, pictures and members.
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You do mention it was built up by someone with a background in racing, which could explain the lack of advance retard.
Its not uncommon for race engines to be set up with fixed timing set at full advance.
My sidecar has this set up but sadly comes down more often than yours ;)
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Ignition trouble? Plugs first, then points.
I would have to suspect the points, as you have interfered with them.
Gap and clean, for a start. Check clearance of points spring to cam ring.
For a long time, owners would not spend money on an auto advance for an old bike and then later for some time it was difficult to find a working one or get one fixed. As you have found out, some bikes don't need auto or manual advance.
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Thank you for the replies i received to my posting, some time ago.
Since that time, i have timed the beast best i can, and it starts well from cold, ticks over well and runs good at low - medium speed.
However, the timing suffers at high speed, and it coughs and splutters and generally fails to co-operate. (Plus hot starting is bad)
I assume that as the machine was built without either a manual or auto advance, it must have originally been timed accordingly. (to a good working average/approximation)
I have tried all manner of settings to repeat this, without success.
Can anyone shed any light on this and give me a set-up that starts easily and also runs well at all speeds.
Better still, has anyone got the bits for sale, to reinstall either a manual or auto advance?
Many thanks and kind regards
Neil
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^^^
give me a set-up that starts easily and also runs well at all speeds.
Can't be done without some form of variable timing, electronic, mechanical (springs\weights) or manually. Lock at full advance will work, but = rough idling\lower rpm, and risks of broken leg or a week limping and pain killers (kick-back at start).
Here's a NOS autoadvance (http://www.ebay.co.uk/itm/LUCAS-Auto-Advance-Ariel-Huntmaster-BSA-A7-A10-Golden-Flash-Road-Rocket-47503-/151182289468?pt=Motorcycles_Parts_Accessories&hash=item23332aaa3c) ...at a price, but probably quite rare to find these as NOS. Used ones are widely available, but also widely varying quality, so ask about (or see) them before buying. Easy fit. Maybe our mag-experts members here on the forum got some refurbished ones for trade.
Converting mag to manual involves more work, needs new parts \ housing at the points side (and ?maybe? a new cam) + cable and lever.
Research what's the most practical \ economical. Personnaly I enjoyed having manual & handlebar lever.
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Thank you for the replies i received to my posting, some time ago.
Since that time, i have timed the beast best i can, and it starts well from cold, ticks over well and runs good at low - medium speed.
However, the timing suffers at high speed, and it coughs and splutters and generally fails to co-operate. (Plus hot starting is bad)
I assume that as the machine was built without either a manual or auto advance, it must have originally been timed accordingly. (to a good working average/approximation)
I have tried all manner of settings to repeat this, without success.
Can anyone shed any light on this and give me a set-up that starts easily and also runs well at all speeds.
Better still, has anyone got the bits for sale, to reinstall either a manual or auto advance?
Many thanks and kind regards
Neil
I'm sure you can source one closer to home but am sure there's one unused on the shelf if interested, but am away all weekend.
In terms of running fixed ignition, always set at full advance. My cooking B33 has manual ignition and I only ever retard it when stopped at lights. As soon as its on the move its fully advanced. Full advance usually applies from extremely modest rev's.
My fixed timing A10 pulls like a train right through the range and well tickled starts easy enough with a push (no kickstart fitted).
coughing and spluttering doesnt sound like ignition unless well out. Poorly timed bikes typically either feel flat, wont rev or lack torque.
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There are a couple on eBay if your still looking?
http://www.ebay.com.au/itm/BSA-A7-A10-Lucas-Auto-Advance-Unit-Used-/131001788961?pt=UK_Motorcycle_Parts_13&hash=item1e8050aa21&_uhb=1
http://www.ebay.com.au/itm/Triump-bsa-pre-unit-lucas-magneto-auto-advance-unit-/331100307472?pt=Motorcycles_Parts_Accessories&hash=item4d171dc010&_uhb=1
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The bike has gone well since the 1980s. Whatever is wrong now, it's not lack of an auto-advance.
It must be set to the correct fully advanced timing figure.
Have you done the simple things like checked fuel flow and main jet? Is the problem related to rpm, or throttle position?
Worst case is a magneto needing to go to Tony Cooper.
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I'm in agreement with Triton Thrasher, sometimes new points do bed in quite a lot and the gap can dissapear
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And if that be the case, closing the gap retards the timing, hence fine down low but crap at revs. Will also overheat and blue the pipes.
Cheers
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Points gap is a service item.
If you don't attend to all the service items in the Service Sheets, you'll get no sympathy from me.
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Hi All,
After 20 odd years the magneto is well overdue a servicing !!!
I have seen an A10 which had all the symptoms described , it turned out to be a faulty mag slip ring
HTH
John
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I've also seen modern points plates break. But then you wouldn't get any spark.