Spark occurence?

[jaffa90]

Not bikes but static ignition timing on a petrol strimmer with a two legged solid state coil and a fly wheel with a north and south magnets, my question is when does it spark ?
When both magnets line up with the two legged coil or when the last magnet passes the last leg on the coil?

[stinkwheel]

Assuming it's a hall effect sensor.. Um depends which way round the sensor is wired in but that's probably an irrelevant layer of subtlety for a strimmer.

On a strimmer, in the absence of any markings to the contrary, I'd take the timing point to be when the trigger magnet is halfway along the sensor, there's often a line on the sensor. Sometimes also some markings on the rotor in which case I'd go by them.

In a more complex way of looking at it, if the trigger hits the positive leg of the sensor first, it's just after the rising edge passes. If the trigger hits the earth leg of the sensor first, it's just after the falling edge passes. If you have opposite poled magnets at 180 degrees, it could do it one way on one and the other way on the other.... So yeah, middle would be my vote.

If you've got it set and it's latchy to start and pinking at higher revs with a white or nibbles plug electrode, retard it slightly. If it's easy to start but down on power with a dark coloured electrode, advance it slightly.

I'm surprised you're able to adjust it. I'd have expected it all to be keyed in place
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[jaffa90]

Thanks for the reply and the flywheel is keyed in place and magnets and coil legs line up about 40 degrees after top dead centre in the correct rotation. I`m going to file another keyway and JB cold weld it instead of buying a new one because this looks original.

[A100man]

[stinkwheel]

Equally, if everything is fixed in place in factory positions with no adjustment possible and you're considering altering the keyway position, you're probably barking up the wrong tree. Unless the timing shaft has spun in the crank?

WDforte may be along soon, he has a very good understanding of the intricacies of electronig ignitions.
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[jaffa90]

I had the same problem years ago with a Stihl non runner covered in oil, i checked if the flywheel was the correct one with no joy, so i filed another key way and away it went without blowing oil out.

[jaffa90]

Some pics with the piston at top dead centre (TDC) and magnets no where near and rotating anti/clockwise.

[WD Forte]

'Solid state' coil? you sure?
I have no experience with strimmers but my initial guess
based on a first brief look.

I'd have said its just a potted coil and the magnet passing
the two 'legs' builds and collapses a magnetic field in the
LT winding.
This build and collapse induces a high voltage on HT side
which discharges via the spark plug.

Timing like on lot of these wee motors would be there or thereabouts
and fine for a relatively fixed speed.

Again just guessing, but I'd assume the LT windings to be insulated from the body so any leaks to ground from bad insulation would dampen power
Like most coils I'd look for low resistance in the primary side and
high resistance in the HT side
____________________
bikers smell of wee

[jaffa90]

Solid state' coil? you sure?

I thought a solid state coil had no points or a condenser.

Q, what position would the magnets be in with the legs of the coil when a spark occurs?

Granted it`s a fix timing.

Also this strimmer has had very little use (stored for about 10 years) but signs of oil around the carb and exhaust.

[WD Forte]

Semantics I suppose
Solid state to me is using transistors/mosftets n shit for triggers and
power switching

That appears to be just simple electromagnetic system
where a magnetic pole sweeps past the primary coil at one leg to create an electromagnetic field which quickly collapses when the other (reversed) pole sweeps past to induce a current in the secondary HT windings.

EM fields build and fall very very fast but not instantly
so I assume the rotor magnets position in relation to the coil legs
has been designed to do this at an optimum time.
____________________
bikers smell of wee

[stinkwheel]

Yeah, that's not what I thought it was. A hall effect sensor is about 2x2cm.

I wonder if those two rectangular holes are significant and trigger the breakdown? I think the only way to be sure of the timing point there is with a strobe.
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[jaffa90]

""That appears to be just simple electromagnetic system""
I agree,

"""I wonder if those two rectangular holes are significant and trigger the breakdown?""""
These are open cooling fins in between the magnets and dummy weights on the opposite side for balance.

I have managed with patience to position the magnets in the middle of the coil legs at T.D.C.

As far as manufacturers quality look on ebay daily deals for tons of refurbished items.

[WD Forte]

As per Stinkwheels suggestion, I'd use the original keyway unless there's a compelling reason to change it.

Do you have a spark?
if not I'd be testing the coil before changing the rotor position
and also check the kill switch isn't shorting to ground
____________________
bikers smell of wee

[jaffa90]

When i start checking a non runner i remove the plug and spray oil in there, next i check for compression / suction and then a spark with a non resistor plug and then the kill switch. After that i remove covers and the carb and check the ignition timing.
I have repaired a lot of these engines and found that the magnets give a ratchet effect when rotating the flywheel/rotor at T.D.C.
I have a strobe but no access because it is all enclosed when built.

[stinkwheel]

[jaffa90]

Well i`m gobsmacked, i reset the fly wheel with the magnets on both coil legs at T.D.C as i`ve seen / felt on many of these 2 stroke engines before but found that using a strobe light ( used many years ago when checking for mechanical and vacuum advance timing) it flashed 45 degrees to early so i fitted the flywheel back to the original position.
In future and if any doubts i`ll use the strobe.
So i thank you both Stinkwheel & WD Forte for your advice.
Q, how can an ignition coil spark 315 degrees after being excited ????

[Nobby the Bastard]

That's nothing, I've known Mrs bastard to orgasm 3 days after I excited her.
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