Author Topic: Can ignition timing go faulty during use?  (Read 1609 times)

Online owain

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Can ignition timing go faulty during use?
« on: 11.02. 2019 21:37 »
It's been a few months since my A10 suddenly stopped working whilst I was out riding. The next day it was incredibly hard to start (I had to run down the road and drop into second) and when it did start it would only stay alive with a lot of throttle. The day after that it wouldn't start at all.

The magneto had been reconditioned by APL magnetos in June last year. Both cylinders have 150psi. And I recently replaced the auto-jumble concentric carburettor with a brand new concentric carburettor ( a 928, .240 main jet, .106 needle jet, throttle slide 3, needle pos. 2).

I'm back at trying to get the bike working again now. Fresh fuel in the tank yesterday but I'm getting little sign of life out of it. Perhaps the occassional 'pop' out of the carburettor but no kick back from the pedal (I remember a poorly timed B33 almost snapping my leg with a strong kick!). Even with the new carb not being correctly tuned, I'd expect there to at least be splutter or a brief moment of continuous ignition. The only thing I have left to think of is that the timing is off. It is an auto-advance timing btw. The irritating thing is that I ensured that the timing was set up exactly (11/32" BTDC with auto-advance unit wedged in full advance) and it worked grand for a few weeks. So how could the timing go bad so quickly? Is it possible that it rotated out of it's position during operation? Is that normal to happen with only  a few weeks worth of short distance riding?

Would love to hear what advice might be out there. Thanks!
Sweden & North Wales
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Offline morris

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Re: Can ignition timing go faulty during use?
« Reply #1 on: 11.02. 2019 21:50 »
Quick check; remove the pickups and have a peek inside if there’s a trace of carbon on/around the slipring. Bad quality brushes leave a trace of carbon and will create an arcing path for the spark to go anywhere except to the plugs
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Offline chaterlea25

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Re: Can ignition timing go faulty during use?
« Reply #2 on: 11.02. 2019 22:06 »
Hi Owin,
Has it wet sumped while standing?
A sumpful of oil can prevent getting a good kick over
A quick stationary check of where the points open without stripping off the timing cover will tell a lot, clean the points too
they should open about top dead centre, (there or there abouts is fine)
Is there a good spark at the plugs?

John
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Offline Swarfcut

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Re: Can ignition timing go faulty during use?
« Reply #3 on: 11.02. 2019 22:09 »
Following on from morris, check that when the points open, the plug lead to the cylinder on compression is the one which is contacting the brass segment of the slip ring. We have all swapped the leads over by mistake. Pick up brushes must be clean and free to move. Remove the points cover, in case the maggy is earthed somehow and check for good sparks at the leads.  Timing can slip, but you should get some sparks if the maggy is being driven. Like they say, most carb problems are ignition.

 Swarfy.

Online Greybeard

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Re: Can ignition timing go faulty during use?
« Reply #4 on: 11.02. 2019 23:02 »
Ignition timing will change if the points gap changes. Too wide, spark retarded. Too close, spark advanced.

Online Black Sheep

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Re: Can ignition timing go faulty during use?
« Reply #5 on: 12.02. 2019 06:49 »
Yes, the timing can slip especially if it has recently been set. It's not too difficult to check with the calibrated stick down the plug hole technique. It will give you a fair idea if there's anything badly amiss.
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Offline a10gf

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Re: Can ignition timing go faulty during use?
« Reply #6 on: 12.02. 2019 06:57 »
Some causes that needs checking\eliminating.

Removing the plugs and 'earthing' them, do they show a good, strong spark even with gentle kicking.

If a good spark, check timing, the autoadvance could have slipped on the magneto, has happened to me (with fixed gear) due to not securing the nut properly, while riding the bike behaved worse and worse then stopped net a few miles from home.

Regarding carb & fuel supply, after kicking (or pushing) for a while and getting no start, there should clearly be 'wet plugs' + fuel smell from silencers.

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Online Klaus

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Re: Can ignition timing go faulty during use?
« Reply #7 on: 12.02. 2019 08:12 »
Ignition timing will change if the points gap changes. Too wide, spark retarded. Too close, spark advanced.


Are you realy sure?
I say its the other way.
If the gap is bigger, the contactbreakershue is closer to the camring and the shoe is tuching sooner the ramp. This means the ignition is advanced.

cheers Klaus


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Offline duTch

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Re: Can ignition timing go faulty during use?
« Reply #8 on: 12.02. 2019 08:15 »

 
Quote
.....? Is it possible that it rotated out of it's position during operation? Is that normal to happen with only  a few weeks worth of short distance riding?...

 Only you the owner/ Rider can verify that with an easy check
Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
Have a '74 850T Moto Guzzi since '92-best thing I ever bought doesn't need a kickstart 'cos it bump starts sooooooooo(mostly) easy
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Online Triton Thrasher

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Re: Can ignition timing go faulty during use?
« Reply #9 on: 12.02. 2019 08:53 »
If you’re the slightest bit worried about points and timing, check the points and timing.


If the points close up, the ignition retards.

If the drive pinion slips on the tapered end of the armature shaft, the timing retards.

Offline Swarfcut

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Re: Can ignition timing go faulty during use?
« Reply #10 on: 12.02. 2019 08:54 »
Points and Timing. I'm with Klaus on this one. On a conventional fixed points/ moving cam set up, opening the gap brings the fibre heel of the moving point, at rest, closer to the cam. So the cam has less distance to rotate to open the points, so advancing the timing. Logic would say it does not matter whether the cam is fixed and the points rotate. False logic? So we need a definite answer from our electrical department.

  Checking the timing with the ATD in its retarded position.....Someone measured the piston height, but fool that I am, I  did not make a note. It must be somewhere on the Forum.....a useful dimension for a quick check before things get a bit oily.

 Swarfy.

Offline Rex

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Re: Can ignition timing go faulty during use?
« Reply #11 on: 12.02. 2019 09:29 »
Personally I would investigate the carb and in particular the pilot jet/idling circuit. Do the plugs get wet? Will it run with a squirt of fuel in the cylinders or in the air intake?

Online Greybeard

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Re: Can ignition timing go faulty during use?
« Reply #12 on: 12.02. 2019 09:36 »
Ignition timing will change if the points gap changes. Too wide, spark retarded. Too close, spark advanced.
Are you realy sure?
I say its the other way.
If the gap is bigger, the contactbreakershue is closer to the camring and the shoe is tuching sooner the ramp. This means the ignition is advanced.
Yes, you are correct. I was thinking of car distributors where the cam is inside the points heel. Of course on our bikes it's outside of the heel. Sorry if I confused anyone.

Anyway, points gap affects timing.

Offline duTch

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Re: Can ignition timing go faulty during use?
« Reply #13 on: 12.02. 2019 09:52 »

 
Quote
.....The magneto had been reconditioned by APL magnetos in June last year....

 Yeah but the fact you had it 'reconditioned'  means Jack-shit as per my earlier reply to another thread on this..... did you have it  checked out by the refurb guy,  and/ or an independant someone as I inferred  you should??
 If you don't follow up or feed back on suggestions,  we can't help much as we'd like

Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
Have a '74 850T Moto Guzzi since '92-best thing I ever bought doesn't need a kickstart 'cos it bump starts sooooooooo(mostly) easy
Australia

Offline Colsbeeza

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Re: Can ignition timing go faulty during use?
« Reply #14 on: 12.02. 2019 10:24 »
Hello Owain,
All that has been said should dictate your check list. However, if a solution does not happen after all that you may need to get the magneto bench-tested. I had my magneto timing shift soon after having it overhauled and then checked again. So a magneto fault is a last resort. Took me months to pin that down. The serviceman could not explain why it happened.
Cheers Col
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