when one look at the old two-stroke inboarders, allmost everyone has a magneto, which is adjustable, so when you start, you set the ignition at low, to prevent the engine to run backwards, when it works the ignition is set to high. A BS. is not adjustable, and therefore the ignition is set to low, in order not to go the wrong way around, this cannot be the most efficient use of the motor, so has anyone tried to make the ignition adjustable, by changing the things, so the plate could turn a bit, to a higher ignition point.
lower being late
high being early
Allmost any other outboarder changes ignitionpoint to higher, when giving trottle.
good summer to you all. and don't forget the oars.
Just wondering.
Moderators: John@sos, charlesp, Charles uk, RickUK, Petergalileo
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Dr.Lighthouse
- Posts: 30
- Joined: Thu May 25, 2006 10:29 pm
- Location: De Panne - Belgium
As far as I can remember, none of my twenty-odd two-stroke motorcycles came with a variable timing.
The idea behind ignition timing is to try and time the peak combustion to apply the most efficient pressure on the descending piston.
As rpm increase, less time is available for the mixture to burn, so it will need to be ignited earlier to account for the diminished time.
Since British Seagull two-strokes have a very basic combustion chamber and run at fairly low rpm, there is no need for a variable timing.
Too much of pre-ignition will only lead to excessive high temperatures, resulting in 'knocking' which in its turn will destroy the big end, not to mention piston seizures or even the odd perforated piston . . .
If you decide to deviate from the stock timing you'll need to be attentive for overheating.
The appearance of the spark plug will be a great help, as excessive timing has a bad habit of overheating the electrodes.
Here's a link to an overview page of 'spark plug diagnosis':
http://www.spark-plugs.co.uk/pages/tech ... gnosis.htm
Conclusion: leave the ignition as British Seagull has designed it !
The idea behind ignition timing is to try and time the peak combustion to apply the most efficient pressure on the descending piston.
As rpm increase, less time is available for the mixture to burn, so it will need to be ignited earlier to account for the diminished time.
Since British Seagull two-strokes have a very basic combustion chamber and run at fairly low rpm, there is no need for a variable timing.
Too much of pre-ignition will only lead to excessive high temperatures, resulting in 'knocking' which in its turn will destroy the big end, not to mention piston seizures or even the odd perforated piston . . .
If you decide to deviate from the stock timing you'll need to be attentive for overheating.
The appearance of the spark plug will be a great help, as excessive timing has a bad habit of overheating the electrodes.
Here's a link to an overview page of 'spark plug diagnosis':
http://www.spark-plugs.co.uk/pages/tech ... gnosis.htm
Conclusion: leave the ignition as British Seagull has designed it !
Thanks for your answar.As far as I can remember, none of my twenty-odd two-stroke motorcycles came with a variable timing.
The idea behind ignition timing is to try and time the peak combustion to apply the most efficient pressure on the descending piston.
As rpm increase, less time is available for the mixture to burn, so it will need to be ignited earlier to account for the diminished time.
Since British Seagull two-strokes have a very basic combustion chamber and run at fairly low rpm, there is no need for a variable timing.
Too much of pre-ignition will only lead to excessive high temperatures, resulting in 'knocking' which in its turn will destroy the big end, not to mention piston seizures or even the odd perforated piston . . .
If you decide to deviate from the stock timing you'll need to be attentive for overheating.
The appearance of the spark plug will be a great help, as excessive timing has a bad habit of overheating the electrodes.
Here's a link to an overview page of 'spark plug diagnosis':
http://www.spark-plugs.co.uk/pages/tech ... gnosis.htm
Conclusion: leave the ignition as British Seagull has designed it !
I don't know about your bikes, but 99% at least of all 2 stroke outboarders has the ability to chance timing, in fact they are forced to do it, all the small inboarders 2-8 hp I have seen, have the facillity, here in a manual way, and it has a clear function. As many of the magnetos came from UK. I am sure the same type of motors were running there, and still are . If you start them in early position, they will many times try to go backwards and when started with a belt, it's pretty dangereus, many has hurt their hand badly, even lost a finger. Even worse with a handle, spinning the wrong way around. These things are facts, not any theory. So I think the manufactors of BS has made a compromice by setting the timing in a safe way, to avoid misshapps, and make it simple to produce and maintain, but perhaps not the most efficient solution. I seame to remember reading, that a person has changed the motor, in order to , by hand, adjust the timing so early, that he was sure it started backwards, to
use as a kind of reverse gear. I don't remember where I read it, or if it mensioned any improovement, when only changed a little.
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timberman2004
- Posts: 375
- Joined: Wed Apr 02, 2008 11:11 pm
- Location: Lerryn Cornwall
timing
According to my father in-law the J.A.P 2stroke engine was about the only 2stroke available at one time and with no adjustment of timing when running, I have five outboards of the 50s/60s and the only one with an adjustable timing, and thats a 1947 USA made outboard, and has a tendency to cook its ignition system, the seagull was a basic outboard with a basic 2stroke engine that ran for ever, it works so why change it.
And anything in the wrong hands is dangerous.
And anything in the wrong hands is dangerous.
All of the old bikes I owned ( 2 & 4 stroke ) had adjustable timing, dont forget although you set the timing statically ( well you did in those days 
) they were fitted with an automatic advance / retard unit wiv ikkle centrifugal weights to advance the timing as the speed increased, before that the timing was on a lever ( much the same as a seagull throttle ) on the handlebars.
I would imagine the original poster is correct and a seagull might benefit from a more complex ignition solution but then they wouldn't be so simple would they? if you don't really need it why complicate things? Remember the Americans in the 60's produced a magnificent ball point pen for use in space, very high tech, wonderful piece of kit and it could write upside down all day, the russians took a pencil. ( probably hypocryphal but you get the idea, if 3-4Hp is OK y change )
As a matter of interest, I am aware that CDI circuits can be made that do incorporate some kind on advance / retard function, any of our experts know if any of the seagull units do?
) they were fitted with an automatic advance / retard unit wiv ikkle centrifugal weights to advance the timing as the speed increased, before that the timing was on a lever ( much the same as a seagull throttle ) on the handlebars.I would imagine the original poster is correct and a seagull might benefit from a more complex ignition solution but then they wouldn't be so simple would they? if you don't really need it why complicate things? Remember the Americans in the 60's produced a magnificent ball point pen for use in space, very high tech, wonderful piece of kit and it could write upside down all day, the russians took a pencil. ( probably hypocryphal but you get the idea, if 3-4Hp is OK y change )
As a matter of interest, I am aware that CDI circuits can be made that do incorporate some kind on advance / retard function, any of our experts know if any of the seagull units do?
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Charles uk
- Posts: 4972
- Joined: Wed Feb 27, 2008 4:38 pm
- Location: Maidenhead Berks UK
There are 2 styles of CDi a white Mk 3 Wipac & a brown Mk 4 Wipac.
I have measure the white Mk 3 Wipac & at circa 2000 revs the spark seems to advance from the low 20's to somewhere between 25 to 28 degrees before TDC.
The brown MK 4 I'm told does the same.
Do not swop the flwheels around between these 2 types of CDI's they never seem to work properly, & the white type flywheel, "no groove on the periphery" will damage terminally the brown Mk 4 CDI.
I have measure the white Mk 3 Wipac & at circa 2000 revs the spark seems to advance from the low 20's to somewhere between 25 to 28 degrees before TDC.
The brown MK 4 I'm told does the same.
Do not swop the flwheels around between these 2 types of CDI's they never seem to work properly, & the white type flywheel, "no groove on the periphery" will damage terminally the brown Mk 4 CDI.
Ooooo er! I don't like the terms 'damage' and 'terminal' in the same sentence 
Thanks for the warning Charles. Wasn't planning swapping anything but as my 90 is Mk 4 I will be careful. The older 90 I haven't checked out yet, but as I had heard the Mk4 ignition was much better I suppose I might have been tempted to replace it if it proved to be a Mk 3 and not in the best of health, will think twice now!
Thanks for the warning Charles. Wasn't planning swapping anything but as my 90 is Mk 4 I will be careful. The older 90 I haven't checked out yet, but as I had heard the Mk4 ignition was much better I suppose I might have been tempted to replace it if it proved to be a Mk 3 and not in the best of health, will think twice now!