left cylinder wont fire past idle

[project94]

Hey guys,

I'm a bit stumped with my left cylinder and was wondering if I could get some help.

Picked up a non-running 94 project bike and so far the valves were adjusted, carbs cleaned, new head and base gaskets, and new plugs were put in. There is good compression with 130 on the left and 140 on the right and plugs were visually checked for spark.

If the bike is started up with only the right plug boot plugged in, it fires up and rev's just fine. The bike starts up with only the left boot plugged in too but the idle is a bit rough. If given any gas (up to WOT) on the left cylinder, the rpm's will raise by a couple hundred and just sputter and hesitate, never really getting out of idle speed.

I'm kind of stumped and not sure where to check next. If the resistances check out for the rest of the ignition system, can it be a CDI issue? Thanks guys, any suggestions would be appreciated.

[jestercinti]

A comprehensive list of things to try:

1. Plug. Switch with other side. Could be weak spark.
2. Coil or wire. Buy a shop manual if not already. There is a resistance check. Or just swap coils and see if the problem moves.
3. Battery. Not enough juice means not enough to spark at high speeds.
4. Ignition pickup. There's a test procedure too in the shop manual.
5. CDI box.  Not sure if there is a test procedure.  May need an expensive OEM tool.
6. You should look into valve clearance and carb air leaks next if ignition does not yield good results.

[adidasguy]

Since it idles and craps out with throttle, my uneducated guess would be clogged jets in the carb on that side.

[BockinBboy]

Since it idles and craps out with throttle, my uneducated guess would be clogged jets in the carb on that side.

This.

Also, check float heights to ensure adequate fuel delivery to both carbs.

- Bboy

[The Buddha]

Probably a blocked pilot.
Cool.
Buddha.

[project94]

Thank you for all your replies.

To eliminate it being a carb problem, carb cleaner and a thin copper wire was used to ream out all small holes in the various jets. The left float level is a little high when I checked it with the clear tube + float bowl bleed method. Will need to correct that.

Jester:
1) Tried switching plugs, same results.
2) All resistances check out according to manual
3) Same results using a fully charged battery or a jumper unit.
4) Need to do this
5) Yea, I can't seem to find much on how to test the cdi.
6) valves were adjusted. need to take a closer look at possible air leaks on carb.

Adidas:
I've had problems with clogged jets before on my EX500. As soon as I touched the throttle the bike would die, but with the GS the bike will still run. Am I over looking something in this comparison? I would think that if the jets were clogged, the mixture would get way too lean at WOT and die out but this GS just kinda sputters just under 2k.

Again, thank you everyone for your suggestions, I will check back after I poke around the ignition a bit.

[jestercinti]

I wrote that before I had my first cup of joe this morning on the city bus.

DOH!  I think fuel/carbs sounds more like it.

Some more thoughts...The early carbs have this little o-ring visible when you take off the top diaphram plastic cover.  If missing/worn it will run bad.

Look for loose and/or frayed connections.  Sometimes when you move something like the throttle, it causes a wire to move and shorts because it's frayed.  Happened all the time on my 1982 GS450.  Are connections tight on the wiring harness?

Take a look at the parts fiche for the carbs...did the previous owner try to upgrade it while screwing it up in the process?  Look at the jets and needle.

Running out of ideas...Kink or bent hose/tube causing fuel starvation or vent/vacuum problems?

[The Buddha]

Its runs fine @ wot but craps out just past idle ?
Its prolly not electrical.

I still say pilot ... how much higher is the float ?
You may have vacuum leak cos that is a left carb only thing on an 89-00.

Cool.
Buddha.

[project94]

Hey guys,

I finally found the source of the problem but I have no idea how this happens.

Turns out that the signal generator was worn.


Swapped it out with a new one and it runs like a champ. Anyone know how this wear pattern occurs? It almost looks as if the rotor component actually came in contact with it. Does this point to deeper issues [worn bearing], or is this expected with age?

[piresito]

Woooww....curious how you found that out and how that wears!!

[jestercinti]

Wow. Ignition after all.

Had a signal generator connection loose. Drove me batty for 3 days wile I traced it out.

[project94]

Pire: Yea, hopefully someone can chime in on this. I get the feeling that this is not normal.

Jester: I completely understand, I despise electrical problems as they can be so hard to find.

If it isn't too much of a hassle, could I ask someone with an older GS to take a peek at their signal generator? Getting to it is as simple as removing the three 7(?) mm bolts from the right cover. There shouldn't be any oil as there is a seal just behind the rotor component. I'm trying to see if this wearing is a common occurrence.

Thanks again guys.

[piresito]

Mine generator cover is currently off..altough I cannot run the engine at this point yet. What do you me to see in there? Take a picture?


BTW, does that bike has signs of a right hand fall? That could bend the screw/shaft a little....

[adidasguy]

The rotor should never touch the pickups.
I doubt the engine shaft is bent. That is big, hard steel.
The rotor could have the top bent due to a fall on the right side as Piresito mentioned.
Other posibilities:
1. The rotor was not on tight, it came loose and started to eat away at the pick ups.
2. The rotor was put on with dirt under it so it did not sit flat and was at an angle
3. The end of the shaft has a burr, preventing the rotor from seating correctly.
4. The bolt holding it on is bent, causing it to be at an angle.

Most likely is #1. If it was #2-#4, the person assembling it would have noticed it when hand cranking the  engine or when doing a valve adjustment.

[gsJack]

Have a pic of my 02 and you can see there is plenty of clearance between the rotor and pickup, should never touch.  Everything should be tight in there, rotor and coils with no wiggle.  Maybe your rotor was loose at one time like Adidas suggests?

[project94]

Thank you guys. So it seems that the wear pattern certainly is not normal.
I should add that the two screws holding the signal generator was badly mangled, the screw heads are just about stripped. Someone definitely has made a ham fisted attempt at something here.

Before running it, I hand cranked it a couple times with the new one to make sure it would not hit, there was just enough clearance for both ends. I think you guys are right about the rotor being loose at some point, this bike has a very questionable history so anything is possible.

Again, thank you everyone, I think we can consider this solved!

[BockinBboy]

Thanks for completing the thread!  Hopefully it will keep another patient away from Dr. House... 

- Bboy

[project94]

Bboy, I think this might be appropriate:


http://xkcd.com/979/

[BockinBboy]

LOL, Perfect!

- Bboy