Manual Advance Retard

bob · Post by **bob** » Mon Sep 21, 2009 10:41 pm

I've had my 53 model 16 ms for 5 months and love it as a change from my 60 model 31 .
Following the advise for starting and running works perfectly - starts first swing and runs sweet .
But can anybody explain why the magneto lever needs to be 2/5's retarded to start . Leaving 3/5's movement unused .
Or is there conditions when the first 3/5's are used ?

Merlin · Post by **Merlin** » Mon Sep 21, 2009 11:40 pm

Try starting fully advanced the answer becomes obvious

Duncan · Post by **Duncan** » Tue Sep 22, 2009 12:02 am

Bob

I have always believed that it is for slow tickover, but seldom used by most riders.

bob · Post by **bob** » Tue Sep 22, 2009 12:16 am

bob · Post by **bob** » Tue Sep 22, 2009 12:18 am

Hi Merlin
Yes I undersatnd that ( I have tried it ) its not the advance side I was questioning , but the 3/5's unused retarded .
Also mine just dies if I go retarded beyond the starting position

stevie · Post by **stevie** » Tue Sep 22, 2009 1:00 am

I've found the manual advance/retard a most entertaining feature! If it backfires as you drop the throttle when it's warm, a quick fiddle one way or the other seems to balance things up nicely! Why don't modern bikes have them?
In this weather no choke, no advance or retard, quick tickle and one kick and we're away. Fantastic!
Did I mention, I love my bike?

Don Madden · Post by **Don Madden** » Tue Sep 22, 2009 3:02 am

The engine, if properly timed, will tend to kick back if the spark is at full advance while starting & idle somewhat erratically if the idle speed is set there. Retarding prevents the kickback, stabilizes the idle & gives better torque at low RPM. But the spark is weak at low RPM & gets weaker as the magneto is retarded, making starting difficult or impossible if retarded too far. The 2/3 position is optimized for a good magneto & a properly set up carburetor for starting, but can be retarded a little more when idling for a steady tickover.

Cheers, Don.

rgregory · Post by **rgregory** » Sun Sep 27, 2009 12:53 am

quote:
Hi Merlin
Yes I undersatnd that ( I have tried it ) its not the advance side I was questioning , but the 3/5's unused retarded .
Also mine just dies if I go retarded beyond the starting position

The advance lever is a generic lawnmower choke lever and is not matched to the full movement of your magneto advance.

This means most of the lever movement is wasted, and involves some guesswork finding the optimum start position, especially if your cable is a bit loose.

However, with the "pull to retard" arrangement you know optimum full advance is correct by just pushing the lever off.

Cheers,

Rob

rgregory · Post by **rgregory** » Sun Sep 27, 2009 12:59 am

quote:
Try starting fully advanced the answer becomes obvious

HA HA ...

I know a guy with a Jawa 895 speeday motor in an Ariel grasstrack frame with a 5 speed triumph gearbox.

Fixed magneto timing at 34 degrees advance on 14:1 CR methanol.

He kickstarts the thing.

He says "you have to be a bit brutal with the kickstart".

Remind me never to get in an argument with him !!!

Cheers,

Rob

Groily · Post by **Groily** » Sun Sep 27, 2009 8:41 am

All as Don says.
As to 'why's the thing there in the first place?' - because, given that fixing the timing fully advanced was to be avoided for the sake of our legs, Lucas hadn't yet come up with the automatic timing devices that were a feature later on. Or if they had, timing cases didn't have the room for the thing on the drive end of the mag.
Personally, I don't like ATD devices as they mostly mount on those awful fibre pinions which have a tendency to strip their teeth and leave you well stranded. Not a problem for AMC owners. I know of 4 such gears on other marques which have stripped in the last 18 months. One was mine and it was snowing at the time, natch.
However, ATDs do at least ensure that the mag always sparks at its optimal position in terms of armature-to-magnets - which it can't do across the advance/retard range if a movable cam ring or other device interferes with the relationship. Hence as you retard a manual mag the spark weakens, per Don's point.
Since most of us leave their manual ones fully advanced once the engine's running, no problem in practice, and on the whole the arrangement gives very little trouble on singles and parallel twins. Not much use on V twins though . . . .