Glad you got it sorted out the timing can cause havoc!


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One assignment for Zak is to study the GS500 timing and come up with a theory how 1 tooth off can cause hanging idle.
It involved the cross over of the intake and exhaust momentarily being open at the same time and the timing being advanced by 1 tooth (what, 10 degrees?) and how that can result in equilibrium at 4000 rpm.
Any disturbance kills equilibrium and the idle goes back down (hand over air intake or dragging the clutch a little).

Because it is easy to be off by 1 tooth (diagrams are horizontal and engine is tilted at 10 degrees or so and results in a confused brain) this could very well be the smoking gun for hanging throttle that you just can correct when there are no air leaks at all.

I will add that another cause COULD be the timing rotor slipping clockwise a few degrees. Since we use it to crank the engine clockwise, if it slips that would result in the same or similar timing error. I almost removed the timing rotor just to see if it had slipped.

I don.t see how the rotor could be off unless the pin was sheared.  Turning the crank clockwise like you should with wrench would tighten down the rotor if anything.  If both cams were advanced one tooth I think it might be more likely the rotor was not set on the right mark.

Just to muddy the waters a bit more you might want to consider that 4000 rpm is the point where the ignition curves change, they advance from idle to 40* @ 4000 rpm and stay at 40* to redline.

According to my old 97 GS owner's manual the ignition timing was 12* BTDC @ 1200 rpm and 40* BTDC @ 4000 rpm and the  California models were 5* BTDC @ 1000 rpm and the same 40* BTDC @ 4000 rpm.  I assume my current 02 GS is the same as the 5-40 California models.  Unless this is a typo in my old OM the bikes are both the same 40* advance from 4000 rpm to redline.

If you tip your head to the right 15* while timing cams it should all come out OK.

http://www.gs500.net/gallery/data/500/gs500signalgenerators.jpg

Thanks for the additional info.

I is an 89-2002 ignition so it doesn't change timing with RPM as does the 2004+. The 89-2002 has 2 pickups and all they do is fire the plugs. I can't see anything that alters the timing with RPM. Now the 2004+ with the smart ignition box can do that.
I did consider the rotor being sheered so it was off, but adjusted timing first according to the rotor.  Had the1 link adjustment not fixed things I would have removed the rotor to have a look see.

Zak looked at the timing so I chalk it up to him being new at it. A learning experience. I re-checked it after he borrowed Phenix to get home and the motor had cooled down. I am sure some of the other things like leaking cam chain gasket are things which got fixed were good to do. Also re-mounting the head with super extra precision was a good thing (remember the head first had leaks from not being torqued right).

Overall some good learning for Zak and everyone else. We all make mistakes. Here in West Seattle we have a good laugh at whatever dumb thing we do then we all pitch in and fix it.

Funny - this weekend seemed to be the "I thought I had enough gas" weekend. A few guys came over. Amazing how they run out of gas just as they go to leave. It is all good fun. Take gas from one bike so they can get 4 blocks to the gas station. God damn, we have a great bunch of people here. (That battery powered gas siphon/pump from Harbor Freight makes it super easy to steal gas from a bike for another one.)

Not motorcycle related, but I heard the Seahawks won the super bowl. Whatever that is.

PS: Zak reported that his ride home today on his bike was perfect. Runs like butter! Next weekend is try his carbs, lunchbox and get to new fork springs. He did mention the clutch lever needed adjusting. Meh. Simple.

jmill needs another GS so may be that will be the next project bike. Mat is buying Frank. So much going on here. Gorilla getting his motor back together now. 3 motors to check out for projects. Junior needs new clutch plates.

Lots to do. FUN!

HUHSKY and Thumper (thanks to BrianRC) will be in the motorcycle show.

We need a party Saturday after the show Feb 15th. Friday is take-bike-in day and Sunday is take-bike-home day so we could have a Sunday party.

Timing must be advanced at higher rpm's. I always assumed it was done in the igniter box?  The GS450 had a mechanical advance behind the signal generator that the 500  doesn't have.

The 89-2002 GS500 is a stupid ignition box. No relation to RPM. Just 2 sensors firing 2 SCR's (or whatever) solid state  circuits.
2004+ they put smarts into it. The GS500 89-2002 is really stupid: solid state replacing mechanical contact points.

Now to confuse things, I find there are 2 different rotors for the 89=2002 models. The 01D0 rotor has a smaller trip-thingy on the rotor than the 01D1 rotor. So the 01D1 rotor has a larger bump for firing the spark - and it is both wider forward and backward.

I hope Zak can determine what happens when firing is advanced by about 12 degrees (or whatever 1 tooth is as I haven't counted the number of teeth on a cam).

Whatever it is, it would be interesting to know what that error does and why it causes hanging idle. I hope Zak researches it for his school project. As his mentor, I will insist on it. I guarantee I will help him. It is a learning experience for all of is and I think it maybe the smoking gun for people with hanging idle.It is so easy to be off 1 tooth. Engine runs just fine. Just hanging idle when engine gets hot.

We will keep you updated as we do research into this.

Why was the timing rotor changed? What effect is there on the larger trip-bump on the 01D1? If it eliminates a mis-fire and produces better firing then I will seek out the 01D1 and swap out the 01D0 parts.







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Addy, consider this part fact and part speculation on my part.  The spark must be advanced at higher rpm or gas burn will not complete in time to do any good, you would never reach 11k rpm.  The igniter box on the 89-02 GSs  accomplishes this, see this post from Bob Brussard who altered signal coil plates to provide more initial spark advance for members:

http://gstwins.com/gsboard/index.php?topic=6036.msg49692#msg49692

There are 2 different rotors because there are 2 different timings at idle used on the pre 04 bikes.  One for the 12* on 89-00 bikes and one for 5* advance on 01-02 bikes.  And I do believe you would get the 12* advance on the 01-02 if you put a 89-00 rotor on it.  I'm not sure whether or not this would also increase the max advance at higher rpm by 7* also. 

As far as the more advanced black box on 04 and newer models goes there are a couple more functions to be done by it.  The proper rpm signal must be sent to the electric tach and the timing is retarded by the signal from the throttle position sensor when the throttle is opened suddenly under power.

We mention timing curve for the older boxes but I'm not sure if it is a curve, could be just a 2 position selector switch type of thing giving 12* or 40* advance with the change at 4000 rpm?      I only mentioned it in the first place because the typical idle hang up seems to always be at 4000 rpm.

I still think the hanging idle is more associated with the carburation rather than ignition.   

Suzuki parts lists both rotors (01D00 and 01D10) under 1989-2000.
2001-2002 lists only 01D10

The only difference in them is the width of the tab that generates the signal. They are timed the same. The center of the tabs on both models line up exactly the same. Again, the only difference is the width of the tab.

The slightly wider tab: what effect would it have? A stronger pulse? Does anyone know for sure?

I was not aware that the 89-2002 ignition changed timing in any way. Has that been verified or is there a schematic of the insides of the ignition box?

It makes me want to get out the oscilloscope and see what is going on.  If some say the old bikes change the timing but there is no documented proof, then the scope will show it. Dual trace - compare timing rotor pulse to the signal firing the coil. (or wrap a wire around a plug wire and sense the high voltage).

I have a feeling the 4000 rpm hang point might be more related to where the main jet comes in to play. There is some equilibrium point there when the timing is off or someone has the more common air leak.

And considering the timing and cams, adjusting the timing rotor (or pick up position) changes the time of the spark.
Having the cams off by 1 tooth changes the timing of the valve opening/closing in relation to the piston position. (both cams were correct in relation to each other: 18 teeth and both were behind by 1 tooth on the timing chain)
Those are two very different things.

In our situation, I'd like to know how correct spark timing combined with the valves opening/closing one tooth late would cause the idle to hang (not much when cold, but after a few minutes it then was always there).

Quote from: adidasguy on February 03, 2014, 02:15:00 PMI was not aware that the 89-2002 ignition changed timing in any way. Has that been verified or is there a schematic of the insides of the ignition box?

From the Suzuki service manual:

Quote from:  Suzuki GS500 service manual
p 7-35
12° B.T.D.C. at 1 650 r/min.
40° B.T.D.C. at 4000 r/min.

p 9-2, 10-1, 11-1, 12-1 for 90, 91, 92, 93 models
12° B.T.D.C. at 1200 r/min and 40° B.T.D.C. at 4000 r/min
5° B.T.D.C. at 1200 r/min and 40° B.T.D.C. at 4000 r/min ..... E-33

p 13-1, 14-1, 16-1, 17-1 for 94, 95, 97, 98/99/00 models
5° B.T.D.C. at 1000 r/min and 40° B.T.D.C. at 4000 r/min .... E33
12° B.T.D.C. at 1200 r/min and 40° B.T.D.C at 4000 r/min .... Others

p 15-1 for 96 model
5° B.T.D.C. at 1000 r/min and 40° B.T.D.C. at 4000 r/min ... Calif. model
12° B.T.D.C. at 1200 r/min and 40° B.T.D.C. at 4000 r/min

p 18-2 for 01/02 models
5° B.T.D.C. at 1 200 r/min ..... E-03, 28, 33
12° B.T.D.C. at 1 200 r/min ..... Others

p 19-2 for 03 model
5° B.T.D.C. at 1 200 r/min.......P- 28
12° B.T.D.C. at 1 200 r/min.......Others

p 20-4, 21-2, 22-2, 23-2 for 04, 05, 06/07, 08 models
5° B.T.D.C. at 1 200 r/min ..... P-03, 28, 33
12° B.T.D.C. at 1 200 r/min ..... Others

p 24-2 for 09 model
5° B.T.D.C. at 1 200 r/min ..... P-03, 28, 33

Page 19-17 of the service manual actually has a partial schematic of the ignitor showing a CPU that calculates an optimized ignition timing based on the generator signal and throttle position sensor.  The above data suggests that the 89-00 models at the very least had 2 steps of timing; 5° or 12° below 4K and 40° above.  Certainly for 03, but possibly already in 01 there was a CPU to control the timing.

Obvoiusly the timing has been adjusted based on RPM since 89; the question is how and what affect the timing advance mod would have over 4000 RPM.

That does give some more info for research. Might explain why 4000 rpm is that magic point for a hanging throttle.

FYI: Throttle position sensor was 2004+. The control box for 89-2002 is not the same as 2004+.

Quote from: adidasguy on February 04, 2014, 01:11:51 AMFYI: Throttle position sensor was 2004+. The control box for 89-2002 is not the same as 2004+.

Well the service manual shows the TPS connected to the ignitor for the 03 model; but in the US there was no 03 model.

Hopefully you can figure out what's going on

Quote from: radodrill on February 03, 2014, 07:23:38 PM.............................The above data suggests that the 89-00 models at the very least had 2 steps of timing; 5° or 12° below 4K and 40° above...................

If someone with a 89-00 model would put a timing light on the marks and rev it up we could see if it was a stepped change at 4000 rpm or if it was a gradual change from idle to 4k. 

My 02 is frozen in a sheet of ice in my old garage with the battery out right now but I'd like to observe the timing changes on it when I can.

I do intend to check this out. The oscilloscope can do it. Timing light probably could be made using an LED connected to the input of the coils.

Once we determine the timing, then we need to determine why that is the magic point for hanging idle - a strange state of equilibrium.

Service manual just shows ignition as a box. No details of what is inside (89-00 book). So testing will have to be done.

had my legs up after the surgery, was playing with the oscilloscope ive got here testing everything. those thines are awesome, will tell you pretty much ANYTHING you need to know

Well,
Interesting this should come up! A year or so ago this was happening to Flick finally replaced the head. Now we are 7,000 miles later and the same thing is starting to occur after he is good and heated up the idle will shoot up to 4 grand at a stop. I've got a new gasket coming in but not sure other than valve clearance and compression test what more should I be looking for?
Mary

Exactly the same - check the timing and valve clearances. Have intake in spec and like most people here, exhausts on the looser side of things.
With just the valve cover off - check timing carefully.
It might be that timing is OK or pretty good when first done. But with the timing chain lose, it could look good then go a little off when the tensioner is released and pressing on the chain.
I swear we triple checked everything. Changed intake o-rings and everything else was like new. Still problem when warm. Then that night I just had to figure it out. Studied the timing and it now looked off by 1 tooth. The cams were 1 tooth counterclockwise of where they should be - understandable if the timing chain was not tight. When tightened up, it would pull the cams counter clockwise.
I moved them clockwise 1 tooth then they were spot on. Engine has been running perfect since then. Same carbs and everything else. Runs the same with throttle minus a little backfiring (and no hanging throttle).

And we also did tests of 2 different sets of carbs and stock & lunchbox air boxes. Fiddled with mixture screws (we have long boy mixture screws so easy to fiddle with). Nothing mad any difference. Everything looked find and ran fine other than the hanging throttle.

When you figure the diagrams are horizontal, the motor is about 15* angle and the timing chain is not tight then you could easily get off by 1 tooth.

I've joined this group of hanging idlers for the past 2 weeks..




http://www.youtube.com/watch?v=mXng03ICnzw





I got this bike from a friend who couldn't get it running for a long time, I got it running and now it's got this issue. I've checked timing marks, I've rebuilt the carburetors a couple of times just to make sure jets/ports are open and not clogged, I've removed, cleaned, and sealed the boots that mount the carburetors onto the head, and it's all doing the same thing.

I've gone now to taking the carburetors apart again, and will be replacing all of the O-rings that hold the needle seat, and the float assembly. The rings that were in there were fairly dry, but weren't holding the seats firmly onto the carburetor assembly.

Another check, did you check the throttle butterflies, or a stuck choke?

I checked the throttle butterflies last week, one was actually bent, it was confirmation why I couldn't get both carburetors to sync, the choke assembly I had apart since Friday, I took it apart, cleaned, tried to lubricate the sliding shaft, and put everything back together last night. I used an automotive o-ring kit to replace the needle seats' o-rings, and it now provides a seal, big difference.



Here's the old on the left, and on the right a new one, I went with a 1 size smaller than that so it's a tighter fit.

And I'm gonna bet, it will still hover - unless you did something you haven't mentioned in your last 2 posts.

Hovering is due to sucking air - intake or exhaust side, or being lean.
Bent butterfly - may not matter at all, I've seen em with a plier mark on them and looking horrible, and the bike ran fine.
You can synch it, but it may not synch if you are taking in air in 1 cyl. So there is a clue for you, look for air entering into intake.

Cool.
Buddha.