Just another question.....Kerry you are more than welcome to answer...haha

[Thrash67]

What does it mean "Ignition advanced by 5"?

[Ry_Guy]

5 degrees? I had my ignition advanced by 5 degrees back in the day (from Bob B).

[Kerry]

Wow - back for more already, eh?    OK, but this will make more sense if you've already thought fairly deeply about the 4-stroke internal combustion cycle.

Let's concentrate on the combustion stroke.  Think about the point in time where the piston is right at the top of its travel, having compressed the fuel/air mixture into the smallest space possible at the top of the cylinder.  It seems like this would be the best time to ignite the mixture by energizing the spark plug, yes?

Well, it isn't.

If you wait until "top dead center" (TDC) to fire the plug, you will lose out on some of the "push" you could have gotten from the ignited and expanding mixture.  It takes time for the "flame front" to propagate through the mixture, and the piston will have already started to recede from TDC.  In a way, the flame front has to "chase" the piston back down the cylinder.  That's probably not a very precise description of what really goes on in there, but it should give you some idea.

Whatever the "real" reason is, the plug is normally fired several degrees (of the crankshaft) Before Top Dead Center (BTDC).  At higher engine speeds, the momentum of the engine is plenty sufficient to compress the mixture that last little bit, even though the plug has already fired and the mixture is already starting to burn.  Besides, at higher engine speeds the piston spends very little time approaching and receding from TDC....

Now get this: on GS500s sold in California, the plugs are fired at 5 degrees BTDC.  On all other GS500s, the plug is fired at 12 degrees BTDC.   Finally starting to answer your question, you could say that on non-CA models the ignition is "advanced" 7 degrees compared to CA models.  (You'll have to ask an expert to find out why California insists on the 7-degree difference ... must be something to do with fuel efficiency or pollution reduction. 

How does the ignition system "know" when the fire the plug?  On pre-'04 models, there is a pair of "pulse generator coils" behind the bulge on the right side  of the engine (where the "SUZUKI" sticker is).  These coils detect the passing of a metal tab on the very end of the crankshaft, and send a signal to what we call the "black box".  The Haynes manual calls it the "ignition cotrol unit" (ICU).

It's the ICU that actually tells the plugs when to fire, using some algorithm that includes engine speed (and who knows what all else) to determine the ideal timing.  In fact, the ICU "advances" the ignition electronically even further, up to a maximum of 40(!) degrees BTDC, which it reaches at around 4,000 RPM according to Haynes.

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Whew!  Time for a breather before we finish up.  Does everything make sense so far?  Hope so!
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OK, now let's suppose that for some reason you wanted to advance the timing even further.  For example, David Johnson talks about it on the gstwin.com [Racer's Corner] page.  (Search for "Advancing the Ignition".)  He says, "A couple of degrees is as far as you want to go."  But more on that later.

Let's see ... you say you want to know HOW to go about advancing the ignition?  Well, I know of two different ways.  David Johnson actually mentions them both in passing, but doesn't give much detail:

    1) Make the tab on the end of the crankshaft (called the "rotor") go past the pulse generator
        coils a little earlier.

    2) Rotate the plate that the pulse generator coils are mounted on a little bit, so it
        appears to them that the rotor is going past a little earlier.

Method #1 used to be easy.  Vance & Hines (V&H) used to sell an aftermarket rotor that replaced the stock part.  Remove the stock one, put the V&H one on ... done.  It "advanced the ignition" by some number of degrees.  (I can't remember how many, and I'm starting to run out of steam....  )  Unfortunately, V&H stopped selling these aftermarket rotors back in 2003 or so, and they became real scarce real fast.

Method #2 has been documented in good detail by GStwin board members.  Maybe I can do some more searches tomorrow if you come up empty.  (Try search terms like "ignition plate degrees".)  If I remember correctly, someone first came up with a non-reversible method, but then someone else came up with a reversible method. 


At this point, allow me to introduce our very own Bob Broussard, GStwin member and GS500 racer extraordinaire.    As of late 2003, he was "converting" stock ignition rotors for the low price of $5 + shipping.  Whether you sent in a CA rotor or a non-CA rotor, you got back...

a modified rotor that will do the same as a $45.00 V&H rotor (if you could ever find one).

For more details on Bob's original offer, see [THIS OLD THREAD].

Is Bob still offering this service?  I honestly don't know.  I was off the board for about 2 years, returning last Fall, and I don't remember reading much about advancing the ignition in the General GS500 Discussion forum ever since.  You could try PMing him, or emailing him at the address in his profile.  If he's "out of the business", maybe he will document the conversion so someone else could pick up where he left off.  (Maybe he's already done that and I'm just not aware of it.)

Whew!  Will that do for now?

[dgyver]

Yep, Bob is still doing the mod, for 89-02 only (no 04+). I sent several to him last week. He said he does not come around here that much since he semi-retired from racing, but still building GS motors.

[Kerry]

That's good to know.  Thanks for the update, dgyver!