I have worked on a lot of old two stroke motors, motors with cast iron pistons, completely unbalanced cranks, and grease cups to lubricate and seal the crankshaft where it exits the crankcase. And I have never seen an ignition like that. The oldest magnetos I have seen had points of some type. I can't see how leaving the magnetic field would cause a spark. Can you explain it? Eric
Oh, boy, the memory is the second thing to go. I was confusing myself with the old low-tension systems with the points in the cylinder (the "make and break" systems) that we were talking about here a couple of weeks ago. I got them mixed up in my memory.
As for the relationship of magnet to coil and the timing, though, that does apply. That will determine the peak output. However, the points have to open close to that peak, too.
Sheesh. Sorry to be misleading. I hate when that happens.
Yeah, I know all about that failing memory crap. I did know about the points and magnet timing too. Which is why, for example, when a points type ignition on a Briggs and Stratton engine won't spark when the flywheel key shears. Even if it shears only about 1/2 of the key width they usually won't fire because the spark will be too weak. Eric
On Mon, 26 Oct 2015 14:06:48 -0700, snipped-for-privacy@whidbey.com wrote as underneath :
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These modern pointless systems have two hall effect detectors (built into the magneto coil system) to detect the speed of rotation and fix the firing point in software ... and also by default the direction of rotation I assume!! Your split box system I havnt come across - It must still have the timing sense from the coil unit somehow, probably a multiple cable connection to the cdi box. The modern ones only have the plug lead and a kill switch wire, nothing else that shows externally... I happened to have a modern chainsaw partly in bits yesterday so I followed my own advice to you and span it in reverse with the ignition on and watched the plug: correct direction, nice fat spark : reverse direction, nothing... so be warned!! I only ran it at speeds enough to get the spark to work properly and then the same speed in reverse - no test to destructio!! No point in wrecking a perfectly good chainsaw motor! If I were doing this I would correct the position of the coil or the flywheel firing point AND also turn the coil unit upside down so that it all works in the directions as designed... maybe an oscilloscope and metalwork will be involved and there maybe space problems! Could be interesting, keep us informed! At full chat a high speed 2-stroke can be timed near 30 degrees BTDC I believe! C+
Charlie, I have a couple electronic points replacement modules made for the typical lawn mower engine that used points. To use them the wire to the points is cut and connected to the module instead of the points. The only other connection for the module is ground. Anyway, these modules work great and I believe the ignition on the engine we're talking about works the same way. But I was wondering if the direction the coil is wound in relation to the rotation direction of the magnet would make any difference. Fortunately it looks like the magneto coil can be inverted like you suggest. So if coil direction matters it looks like I'll be OK. Eric
On Tue, 27 Oct 2015 09:32:29 -0700, snipped-for-privacy@whidbey.com wrote as underneath :
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Sorry Eric I dont really know the answer to that! Or to the question does it matter that the flywheel magnet is approaching/leaving the coil assembly in the reversed pole direction from designed! My guess would be doesnt matter , but its only a guess! Youd have to experiment if the answer doesnt come from anyone else .. the real circuitry potted into these modern systems seems to be impossible to come by, so your now at the limit of my knowledge on the subject! Post how it goes! C+
The classic 3 cylinder 2-cycle Saab 95 would run either way. Car Talk once had a Puzzler on how one could beat a muscle car in a drag race. The answer was "backwards..." as the Saab could be started the other way and have 4-speeds of reverse...
In my novice race at Lime Rock Park, in the late '60s, I got stuck behind a Saab 93 that had been race-tuned (squared ports, etc.). His secret weapon was that he smoked out anyone who tried to pass him.
I have a weedeat, thats the brand name on it. I put it on my back of my bike. I just happen to ha e a bike that had a braket that worked to put it on ther. Welk after i had it all set up realized that its upsidedown.. And it was firing and a few times acted lke it was going to start... But never did... Now it is on the left side mounted on the bike..i spun the carburetor on it thinking it would work that way... But still failed to start... Thus is the firstbone i have made.. So any ideas on what i need to do... I tried everything.. Cleaned everything... Still has spark..tried spraying gas in the carburetor.... Anyone have ideas... Please let me lnow thanks
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