What would happen if I got spark ~1/2 way down on the intake stroke.

[The Buddha]

Its not just a rhetorical question. I rephased my xs 650. It had a 360 crank, and now its got a 277 crank.
Now its only got 1 trigger point and 1 pick up on the crank and 1 ignition coil and it fires both spark plugs 1 in each cylinder.

The rephased 83 degree motor when one is at on the compression stroke the other is on the exhaust stroke 1/2 way up the cylinder. Firing that is no biggie.

Now the second cyl when its on the compression stroke the first one is running 1/2 way down on the intake.
What will firing it there do ? Kaboom ... maybe but gasoline usually wont light up when there isn't the right ratio of air to gas. Of course it will also fire at compression TDC ... but just wondering ...

BTW it has 15 degrees of advance @ idle and 42 something at 3500 rpm. So it will fire well before the 1/2 way mark on the intake down stroke.

Cool.
Buddha.

[black and silver twin]

I dont know for sure but It sounds like it would actually fire the cylinder. If its on the intake stroke then the AFR would be correct and the resulting explosion would exit the intake valve and possibly damage stuff. I wouldnt trust it. but experiment if your so inclined.

[Suzuki Stevo]

The mixture wouldn't be compressed so... 

[The Buddha]

If it lights up it will pretty much set fire to the entire intake side cos the butterfly, slide etc etc will be open.
I think I have to figure out this bloody thing's ignition one way or another ...
Cool.
Buddha.

[noiseguy]

1/2 way on the intake downstroke? I'd be concerned that you'd be burning up part of the intake charge on that side before it gets a chance to be compressed. That would be lean, and fuel inefficient.

Firing on the exhaust stroke can actually clean up the exhaust emissions. Done on a lot of cars. I assume with the 360 crank that's what it did. Though I didn't realize you could run a system like that with just one coil... I guess it's set up like this:



I think you're going to need to break down and buy another pickup and coil. How do other guys handle this, this is hardly a new conversion.

[The Buddha]

I have to buy another black box, not just a coil.
In fact I have to buy a trigger coil, find a way to fit it, run it to that extra ignitor box and then run stand alone wiring to the second coil ...
The other clowns who do a rephase on an XS switch to the points system of the pre 79, and switch out wiring etc etc and the coild and ignitor box etc ... IMHO that is total garbage.
A 360 twin fired @ the crank only needs 1 coil. Its got wasted spark just like a GS but when its firing wasted spark in 1 cyl, its in the compression stroke on the other. I shifet the right cyl 83 degrees, so that needs to be fired 83 degrees out from original.
The Other way I may do it is, get a ex500 or vulcan 500 or 750 stator, coils ignitor box and igntion coils along with the case cover.

Then fit a yamaha banshee rotor and cut the vulcan case open and bolt it inside that banshee stator. The banshee stator fits the xs crank with no mods, and its backwards, as in open side inwards. That helps in our case - we botl the cut up case onto the crank cases, fit the stator then the rotor on that, fit the trigger pick up's which will have to have carrier brackets made or adapted out of the cases then make the tabs on the rotor etc etc fit it ... I am hoping to then run ex500 ignition on it en masse. I have most of these parts from before.

Banshee rotor and ex500 stator is a known mod, I am just going all the way by triggering the ignition too.

Cool.
Buddha.