How does the choke work?

[ohgood]

Now I'm thinking I'll swap the low-tension connections to the coils - it's wasted spark so I can do that, right?

Hmmm ... it seems like that would only work if the plugs in both cylinders were normally fired at the same time.  For that to be the case, wouldn't the pistons have to be moving up and down together, with a compression & firing sequence that was either exactly in phase or 360* out-of-phase?

Does anyone know the crank offset between the cylinders?  I wouldn't recommend firing the plugs, say, 90* too soon or too late. 

I -thought- it was 180*, but now I'm going to watch your valve video again and make sure...

[Kerry]

180* could be even worse ... firing the plug with the piston at the bottom of the stroke and the cylinder full of fuel/air mixture seems kinda counterproductive. 

[desilva]

According to Haynes K3+ models have only a single pulse generator coil pick up, so it must be 360 deg and both pistons go up and down together. There's nothing else in the loop to introduce an offset if it was required.

[Kerry]

it must be 360 deg and both pistons go up and down together. There's nothing else in the loop to introduce an offset if it was required.

The [CRANKSHAFT diagram] seems to indicate otherwise.    It doesn't provide a good view of the "crank" itself, but the balancers make it look like the strokes would be directly opposed (180*).

If that's true, the compression strokes would be either 180* or 540* apart, right?  (Depending on which cylinder you use as a reference.)  Either way, it doesn't seem like swapping the ignition timing for the plugs would be a good idea.

In the case of the K3+ models, maybe the "black box" is smart enough to time the sparks?  It's responsible for altering the timing anyway, even on the earlier models, so maybe Suzuki went for simplicity (single pickup) via extra complexity (circuitry in the black box)?

I dunno ... where's an expert when you need one? dgyver?  Srinath?  Bob?  Anyone?

[desilva]

The [CRANKSHAFT diagram] seems to indicate otherwise....Either way, it doesn't seem like swapping the ignition timing for the plugs would be a good idea.

I have to agree with your crank analysis. Haynes has a small photo of the conrods connected to the crank and it bears out what you're saying. Now I'm more than a little pleased I didn't try swapping the LT connections. You may have just saved me from some serious damage! 

Doing more searching in the forums is steering me towards an earthing problem; auxiliary ground looks like a good suspect right now. If fact, just like Starwalt suggested in this thread three months ago. Note to self: start paying more attention. 

[gsJack]

Yes, the GS500 has a 180* crank and fires cylinders 180* apart.  That's why the 02 and earlier models have 2 signal generators 180* apart and also 2 coils.

The 04 and later GS have only one signal generator but the rotor has 6 lugs, one large one and 5 small ones that provide timing to the electric tach.  The large lug signal keeps the ignition timed to the crank for the first cylinder and the small lugs send smaller signals to indicate speed to the tach.  The "box" must count the signals for the 180* timing of the spark to the second cylinder.  Two coils are still used.

My Honda twins had 360* cranks with both pistons moving up and down together and only one coil that fired both cylinders together, firing one cylinder while burning excess fuel mix at the scavanger point of the other.

[desilva]

That little ICU has more brains than I gave it credit for. 

I set off this morning after wiggling some earthing points and it was worse than ever. It won't idle, anything less than 3000rpm is a struggle for it, and it's shaking itself to pieces. I did a U-turn and headed straight to the dealer where the bike is now waiting for some TLC. I'll post back with whatever they find.

P.S. Subject line updated 'cos the original post was more than a little misleading.
P.P.S. Ah, it doesn't change it for the whole thread. 

[desilva]

I got my bike back from the dealer and it's running like a charm now. Woo-hoo! 

What was wrong? The frustrating thing is they don't really know. They pulled the carbs, stripped and cleaned them and put them back on...hey presto! Now my lovely bike warms up really quickly, choke goes off, she idles low and smooth and (almost) all of the vibration has gone. It would have been nice to know what was going on in the left carb to make it run so badly, but at least I won't have to have that fruitless conversation with the dealer any more ("Yeah mate, that's carb icing that is.")

It's been like that for so long I'm having to re-learn my gear changes. De-clutch..shift..lots of throttle..clutch. It became muscle memory and now I'm unintentionally accelerating after every shift.    Now the sun is threatening to come up, I think I need a really loooong trip for me any my lovely GS to get re-aquainted.   

[Kerry]

What was wrong? The frustrating thing is they don't really know. They pulled the carbs, stripped and cleaned them and put them back on...hey presto!

I figure:  The bike ran when it left the factory, so if I can get it back to the same state it should run just as well again.  The trick is figuring out what the "delta" is ... the difference between factory-new and now.  Getting things clean (especially carbs) is certainly a good first step.  Doing the cleaning and reassembly right can be problematic, I suppose, but yeah....

Thanks for posting the results!