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won't idle low=too much timing?

usefulidiot

Well Known and Active Forum Website User
Non-VOC Member
Having an issue getting my twin to idle well after a magneto refurbishment and re-timing. It idled well and started easily before the magneto work. Amal Concentrics. Pilot jets are NOT clogged. I am no stranger to sync'ing concentrics and have a hard time believing its me failing to tune them right. Right now the bike will only consistently idle at around 1500 rpm or so. During a test ride the power delivery is not as smooth as it was, seems to have some flat spots. Moderately annoying to get started. Whenever i try to bring the idle down to a normal level the bike just fizzles out and dies. I have already tested for intake leaks. I used the rod-timing method to 34 degrees, however it didnt feel like the most precise of operations. I have a feeling the timing is not where it needs to be but i'm not sure what direction it needs to go. I have the pieces on order from the spares company (timing disc, rod, and plug stop) to try and do the job more accurately but in the meantime my natural inclination is to keep experimenting. Too much initial timing?
 

BigEd

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VOC Member
VOC Forum Website Moderator
It may be too much of a coincidence that the magneto refurbishment is the only change. See if the problem goes away after a more accurate check of the ignition timing. If that fails to improve things can you borrow a known good mag to try? Not very technical but an easy black or white way of diagnosing problems by substitution.
Regarding the Concentrics: Check the cheap easy things first. Pull a hose and see if there is there a good flow of fuel to the carbs?
You say that your pilot jets are clear but it might be carb related if internal drillings are blocked. The fuel these days seems to leave deposits when it evaporates over time. Sometimes needs an ultrasonic bath to clear.
Having an issue getting my twin to idle well after a magneto refurbishment and re-timing. It idled well and started easily before the magneto work. Amal Concentrics. Pilot jets are NOT clogged. I am no stranger to sync'ing concentrics and have a hard time believing its me failing to tune them right. Right now the bike will only consistently idle at around 1500 rpm or so. During a test ride the power delivery is not as smooth as it was, seems to have some flat spots. Moderately annoying to get started. Whenever i try to bring the idle down to a normal level the bike just fizzles out and dies. I have already tested for intake leaks. I used the rod-timing method to 34 degrees, however it didnt feel like the most precise of operations. I have a feeling the timing is not where it needs to be but i'm not sure what direction it needs to go. I have the pieces on order from the spares company (timing disc, rod, and plug stop) to try and do the job more accurately but in the meantime my natural inclination is to keep experimenting. Too much initial timing?
 
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Chris Launders

Well Known and Active Forum Website User
VOC Member
How long is it since you had it running last and are they mk1 concentric's. I got a twin from a friend, it had been stood about 3 years (i've had it just over 2 years), when he had it it ticked over ok, when I got it I could'nt get it to tick over properly at all.
Double and treble checked everything, I eventually read the article by John Mosher on Thevincent.com website and followed his advice, drilled out the pilot restrictors .040 and fitted 30 pilot jets, instant tickover. Having done this I realised my Norton Atlas (with single 32mm mk1 concentric) had gradually had to have the mixture screw further and further in over the years until it was now fully in and was losing tickover again,so did the same mod, again instantly much better.
Not reccomending this as a first option but when all else fails it's something to be aware of if you have mk1's
Chris.
 

usefulidiot

Well Known and Active Forum Website User
Non-VOC Member
Fuel flow is good, they are MK1 concentrics. I also read that carb article and did that on my 66 Atlas last year..the bike was running good a few weeks ago, but the spark would get weak when the bike was warm so had the magneto refurbished. This is why i think it's timing related. I'm thinking i wasnt very accurate and the timing is off. What i'm curious about is whether the symptoms i'm decscribing would be of timing too advanced or retarded.
 

chankly bore

Well Known and Active Forum Website User
Non-VOC Member
Most likely too advanced. You need to do timing accurately with a piston stop and a degree wheel. Aim for about 35 degrees full advance.How old is your A.T.D.? Check timing on both cylinders. See "Tuning for Speed" page 156 for a cheap way of accurately getting point of opening on your magneto.You do not need expensive electronics to do this. There are other obscure errors that can cause these symptoms, but I don't want you all discouraged straight away.Let us know of progress. Cheers, F5AB/2A/7945 since 1970
 

BigEd

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VOC Member
VOC Forum Website Moderator
As a general rule if your timing is too retarded the bike may be reluctant to start and the performance will tend to be a bit flat. Too advanced and it can be difficult to start and will be prone to kicking back when starting. You should aim to set the ignition timing as accurately as you can but in this instance a few degrees either way should not cause the faults you are describing.
If we assume an ignition rather than fuel problem then the erratic starting and performance can be an indication of a faulty capacitor. This usually gets worse as the magneto gets hot.
What work was done when the magneto was refurbished? The capacitor is inside the armature so it is a major operation to change. It is usually replaced when the armature is rewound.

Having an issue getting my twin to idle well after a magneto refurbishment and re-timing. It idled well and started easily before the magneto work. Amal Concentrics. Pilot jets are NOT clogged. ...... Right now the bike will only consistently idle at around 1500 rpm or so. During a test ride the power delivery is not as smooth as it was, seems to have some flat spots. Moderately annoying to get started. Whenever I try to bring the idle down to a normal level the bike just fizzles out and dies. ..... I have a feeling the timing is not where it needs to be but I'm not sure what direction it needs to go. ..... Too much initial timing?
 
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Magnetoman

Well Known and Active Forum Website User
VOC Member
There's just no way to know what the person actually did when he "refurbished" your magneto. The fact the bike worked OK before that, but doesn't after, makes the magneto a principle suspect in this, although the symptoms you describe are not those of classic failure of an original Lucas condenser. But, even if the repairman installed a new condenser, it easily may be one without the necessary specifications to handle the high pulsed currents it is subjected to.

Luckily, assuming you have at least one friend, it's easy to eliminate the condenser from consideration. Take the cover off the points and once you get the bike running have your friend watch the points as you move the rpm around from the 1500 where it runs OK to lower speeds where it misses. Your friend should see no more than the hint of pinpoint sparking at the points at all rpm. Any more than that and the condenser is definitely to blame.
 

Kansas Bad Man

Well Known and Active Forum Website User
Non-VOC Member
At times when mags are overhauled and the points are replaced, the points stick at the pivot pin. Clean any preservative from points, clean contacts with a point file, insure free movement of points. To check for lean idle mixture causing fast idle , go to full choke and see if RPM drops, if it does could be the carbs.
 

Simon Dinsdale

VOC Machine Registrar
VOC Member
VOC Forum Website Moderator
I would re check your ignition timing. I suspect it is too advanced. If you advance the ignition timing on a bike with manual ignition control, the idle speed will increase, which sounds similar to what is happening.

With an increased idle due to advanced ignition, if you try and lower the idle via the carbs, what happens is you reach the point where the throttle stop fully closes the slide and the engine stops. The adjustment just drops off a cliff. So I would accurately set the ignition timing and then as it sounds like you have been adjusting the carbs, re-set the tickover with a warm, but not stinking hot engine, and see how it performs.
 
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