mag timing - does this sound about right?

[StephenG80]

Hi - my bike is '54 G80 with manual mag. Before taking her off the road, to start her she needed the timing retarded about 1/8 on the lever and would idle with the timing fully advanced on the lever. Performance on the road was a bit unwilling and vibrated badly over 50mph. I suspected the mag needed re-timing so have now done that (point gap at 0.012th, opening at 0.5" before TDC).

It is now raining so I am not going to take her out at the moment to see how things have improved but on starting her up in the garage she now kicks back unless ignition is retarded about 1/3, starts fine with that setting and now, when timing fully advanced on the lever, is very happy to ref and sounds nice and deep re the exhaust note. She now won't idle on full advance on the lever but spits back and stalls, but retarding the timing about 1/8th now gets a steady tick over and no spitting/stalling at tick over.

Does this latter scenario sound like I've got the timing about right?

I've concluded who ever owned her before me, had the mag timing too retarded (I think - although I am suffering a bit of brain ache now so it could have been to advanced!!!)

Stephen

[spookefoote1956]

Sounds all right to me. You have to remember that there is always a little wiggle factor in a manual advance retard system.

[StephenG80]

thanks spookefoote - something I am never sure of, should the timing be fully advanced as soon as you pull off and just left like that with the exception of: a) retarding it slightly if going up a steep hill, b) when at traffic lights to stop spit back and stalling, c) When you want to stop the bike completely?

[spookefoote1956]

I always ride at fully advanced unless off road trying to emulate Sammy Miller, unsuccessfully!

[dave16mct]

Yes always use full advance except when starting or idling. It shouldn't stall or spit back on full advance when stationary. It should just tick-over fast.
Dave.

[SPRIDDLER]

Sounds fine to me. In spite of one's best efforts, setting the timing exactly right is an art rather than a science and always a bit hit 'n miss to some extent. If you have to retard the lever back an eighth and it starts and runs fine I'd leave it like that. You can always find the best setting by twiddling the A/R lever when out on a run. You'll feel the right setting through your nethers; th'engine will feel freer and willing to rev. It only means you're not getting max retard but as long as you can retard it enough so that it doesn't launch you next door when starting it'll be fine. As a matter of interest the mag is designed to deliver its strongest spark at full advance.
Once I've started my 350 I never alter the A/R lever.
I often wonder at just how precisely bikes really are timed when people advocate their preference between 7/16" or 1/2" BTDC. I take it as an aspiration rather than a manifesto promise. It usually takes me two or three goes before I get it 'close enough for Government work', (as my Dad would say. )

[zwarts]

From your description I would say that you have got the ignition timing right Stephen. I don't agree with some of the other advice given here about where to set the lever under different running conditions though! The manual advance is there to be used and you should not just set it to full advance once off tick-over. Set it to give the smoothest running and best torque for the driving conditions - so it is a constant process of adjustment, unless you are travelling at a steady speed on a straight road with no incline. As a general rule I find that this is particularly beneficial with the AMC 500cc single cylinder engines, but less so with the 350's. You need to think of the A/R lever as being part of the 'engine management system' so don't be afraid to try adjusting it whilst riding and you will soon build up a sense of where to set it for optimum running under different load conditions. The aim should be to use the minimum advance necessary for satisfactory performance. This is all part of the charm of these machines and a skill well worth mastering.
Have fun, Bob.

[StephenG80]

I like that approach Bob - I will become a CEM practitioner!

(CEM= constant engine management)

[leswaller]

From your description I would say that you have got the ignition timing right Stephen. I don't agree with some of the other advice given here about where to set the lever under different running conditions though! The manual advance is there to be used and you should not just set it to full advance once off tick-over. Set it to give the smoothest running and best torque for the driving conditions - so it is a constant process of adjustment, unless you are travelling at a steady speed on a straight road with no incline.

The same applies to the twins, I use the A/R on my G9 almost as much as the throttle

[zwarts]

The same applies to the twins, I use the A/R on my G9 almost as much as the throttle

That's very interesting Les and goes to show how much different engines can vary in their ignition advance requirements. I have two twins, a 1951 rigid framed AJS 31 which is used for Vintage/Classic sidecar racing and a 1955 G11. The 51 AJS is on fixed timing with a Lucas SR2 magneto, runs at 36° fixed advance and starts easily with a determined kick. As it spends most of its life in the range 4000 - 5800 rpm there is no need for any timing adjustment when under way but the tickover is noticeably 'lumpy' - as you would expect when there's no facility to retard it!
The G11 is also non-standard and has '59 G12 heads fitted to take advantage of the larger ports and valves. This bike has manual A/R via a Lucas K2F Competition magneto but seems relatively insensitive to changes in timing when riding. Not sure why this is, but as a result it spends most of its life on full advance (35°) and I only retard it when slow idling is required eg. waiting at traffic lights.
Not strictly relevant but my Model 50 Norton is very sensitive to ignition setting. To get the best out of it requires constant slight adjustments and it responds very well to a retarded setting when climbing hills.
Bob.