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Correct ignition timing for an AD

Posted: Thu Oct 09, 2008 9:35 pm
by pistnbroke
Whats the correct ignition timing for an AD either in degrees advance or piston position BTDC...?

Yes I know its the contact gap and alignment of the base plate that sets it but using the contact gap is the crudest way of setting timing and I would like to put some proper timing marks on it so I can use my strobe .

Spinning with a drill is good for starting it too !!!!

No point

Posted: Thu Oct 09, 2008 10:29 pm
by Keith.P
A seagull has just a set of points, you can set the gap and thats all.
You could set it up with a strobe but with no flywheel mark there would be no point and you could set it up to rev its head off but on tickover it would run like a bag of nails. the engine has no way to advance or retard its timing when its running, so that why its just a standard set up on the points.
I think most two strokes are set up to about 20 deg BTDC.

Posted: Thu Oct 09, 2008 11:10 pm
by charlesp
The factory setting is in fact 23 1/2 degrees BTDC, or close to it. Each motor has that setting sort of 'hard coded' into it, and if the magneto baseplate locking screw nose engages the dimple in the crankcase nose then that's correct.

Many have been found to be a bit out, but it's not critical.

So the dimple has it right.

Posted: Fri Oct 10, 2008 8:35 am
by pistnbroke
thats it then 23 .5 deg ...not a problem to make a timing mark which aligns the flywheel with a fixed point on the engine .

I carnt agree with Pizey that you can do nothing ..set the points then rotate the base plate to get correct timing with strobe attached and lock it place . Makers marks only for guidance and the best they could do in 1947 but things have moved on ....

Over advancing the timing will make the idle difficult which is why I wanted to know the right figures

What speed do you call idle charles ??? ( dont tell me you dont have a lazer tacho !!! or equivalent of tiny tach on the plug lead !!! )

Posted: Fri Oct 10, 2008 9:53 am
by charlesp
Idle speed is whatever you can tick over at comfortably without the thing stalling. Remembering, of course, that while it's at idle (most of 'em anyway) it's not pumping water.

No I don't have a laser tachometer, indeed I don't have any sort at all.

I really can't accept that 'that was the best they could do in 1947' - they were quite capable of putting marks on things, quite capable of putting adjustments into the thing. They went the other way, and aimed for - and got - Classic Simplicity. That's why I'm here.

I rather like the pre-set timing. It removes doubt.

Of course, if you're thinking of racing your AD based motor, then I completely agree with you, the conversation becomes a lot wider.


Posted: Fri Oct 10, 2008 11:24 am
by Keith.P
My point is, that it was made simple to be simple.
All you need to maintain was some basic tools, screwdriver and some spanners, no need of a krypton tuner.
I carnt agree with Pizey that you can do nothing

Posted: Fri Oct 10, 2008 3:58 pm
by 40TPI
pistnbroke wrote: ..set the points then rotate the base plate to get correct timing with strobe attached and lock it place . Makers marks only for guidance and the best they could do in 1947 but things have moved on ....
The practical aspect of setting it off a degree or so from the factory dimple point to tune it brings a problem. One which you may have found by now......the locking screw will tend to slide into the dimple hole as you tighten it up and pull the magneto plate back to the intended factory setting..... especially true if the dimple has become enlarged ("bruised" ) by people making similar adjustments before you! True some plates are a stiffer fit than others and it would appear to have locked but I'd be very wary of it not moving with time, vibration and temperature if my tune point was half in/half out of the dimple hole.


AD Timing

Posted: Wed Oct 29, 2008 10:17 am
by Collector Inspector
It looks as though you want to be able to adjust the advance "On The Go" anytime you wish...........Yes?

Seagull placed the "Dimple Simple" so the Old dears could be roped easy and off ya go.

I am going to get myself into further trouble with the Aristocracy here, please continue on.

Wanting that is not new. Having that with other makes was available and worked especially well even back in the late 30s.

Advance retard levers on the backing plate is easy to do and works very well on other examples of outboards so why not a Seagull.

Fill in the "Dimple Simple"

Put a spring tensioned plate under the "Locking Screw" so as to cause a friction surface on between the top crankcase diameter and the base plate ID. Easy.

Attach a lever under the base plate that can be used to rotate the Base as you wish.


Push lever retard, to the left and start normally. Actually, it will start easier as retarded.

Return lever to a calculated "Centre position" to the right, advanced for throttling up.

Benifit is that you will be able to advance lever on backing plate to the right under full throttle load to achieve what you are obviously seeking.

Use 98 octane unleaded and it will be fine.

Note.....YOU must know your motor and be able to HEAR excessive advance on your lever. "It will sing as you swing". A mechanical Stop can be placed to restrict your new found freedom.............

If you go this path, use a COLD plug.

I think everyone else is going to "GO OFF"

My "Chook 102" has this...............................



Posted: Wed Oct 29, 2008 11:01 am
by charlesp
The method of providing an advance/retard mechanism that you have described was used until about 1936 on the teardrop Marstons. Even after that date, for a while, the factory would supply advance retard to special order, and it wasn't until the SD series that the dimple appeared.

Some of the early ones with a 78cc power head, big Villiers domed flywheel, and the ignition retarded, run, at a very very low tickover, 'like a bar of chocolate' in my mate Andy's words. Smooth and sweet.

I have never been convinced that messing with the factory set timing on later models is at all a worth while exercise.

But of course none of us can resist a fiddle about with something mechanical, can we. Or we wouldn't be here.

Posted: Wed Oct 29, 2008 9:05 pm
by pistnbroke
"Non of us can resist to fiddle about "
You may fiddle about charles but we engineers "modify" and find this style of comment offensive ........I am sure Vic is getting steam up now !!

I am currently working on replacing the contacts with some electronics you realise mowers have not had contacts for years but still use a simple magneto rather than CDI....Then perhaps enlarge the dimple into a slot to give idle and run positions..shame the water pump is so poor .....

any way off on a cruise around Figi etc so no me for a week or so ..perhaps when I get back I will have a photo of the correct filler cap for the AD so I can make on up on the lathe

Posted: Wed Oct 29, 2008 10:28 pm
by niander
another lathe owning showoff! :wink:

Posted: Wed Oct 29, 2008 10:29 pm
by niander
And from downunder! :P

Posted: Wed Oct 29, 2008 10:44 pm
by StephenRT
You really should not denigrate those who “fiddle aboutâ€

Posted: Thu Oct 30, 2008 1:10 am
by timberman2004
Hmmm ...interesting point ...

have to confess that my particular primary interest is taking a 'basket case', and restoring it to as near as original as possible came from the manufacturers

my efforts and experience shows that this does appear to require a fair amount of 'fiddling about', combined with helpful assistance from chaps on this network, in achieving a seagull restoration ....and I do have quite a few to restore / have restored,.... not just the one !

whilst of passing technical interest, rather feel that ammendments, as previously described, bypass the whole spirit of the thing ...

why not just go and buy a modern Mercury or somesuch and have done with it ??

Posted: Thu Oct 30, 2008 1:10 am
by Charles uk
New computer I'm now able to log on & post, WOOOPEE!

During my racing research we have tried all sorts of permutations with the spark timing, all to very little avail.

It's true, that if you retard the spark 5 to 15 degrees you can get a smoother, lower tickover speed, which is no use whatsoever, as there is almost no cooling water flow at normal tickover 1750 to 2200 revs, let alone 1200 revs.

As for advancing the spark for higher performance you will see no improvement until you get up to 5500 revs, a figure your unlikely to achieve unless you take the prop out of the water, at which point you are getting close to your motor's self distruct point!

You will get a far better return on your time if you "blueprint" your Seagull, i.e. make sure all the bearings are running within tolerance, all the ports are high speed gas friendly & the carb is doing it's job as Amal intended.
And please don't forget the gear box & prop, both of which when in poor condition are a huge loss of power.