Very weak spark - have searched - I've tried...

[Robzor]

Hello all - I've reached the end of my ability and knowledge, and am finally asking for help.  Problem presented yesterday, and joy of joys my license exam was today.  That ship has already sailed.

Bike is a 2001 GS500
Symptoms:
Very hard starting - only with heavy application of throttle and won't hold an idle, choked or not
Sounds very very rough

What I've done:
*Checked the plugs.  Heavy carbon deposits, reek of fuel.  Cleaned them, no change.  Replaced them (OEM NGK's), no change.

*First thought was the coils.  Tested them both - primary resistance 5-6 OHM, secondary resistance 25k-28k OHM.  This looks like it's in range.  Tested the +12v terminal, its seeing 12.5V give or take.  Signal must be good, since I get weak spark, not NO spark.

*Pulled the plugs to visually check spark, at beginning of troubleshooting it was too weak to see in direct light, and barely there inside the garage.  After all the troubleshooting, I now get a very weak orange spark.

*Charged the battery, tested at 12V.  Even ran the bike off my car battery, no change.  It cranks the starter just fine, just no good spark.  Voltage increases when the bike is running so I figure the charging system is OK, though the battery was low after having sat only several days...  Maybe there's a clue here??

*Tested continuity of the main ground at the trans case, that's fine.  Visually inspected the aux. ground toward the back of the bike, looks fine but I couldn't reason out a good way to test it..

*Read about problems concerning the 3-wire plug leading to the ignition control, tested resistances from the center wire, they were in range (about 250 OHM), this is regarding the strength of the signal I gather, so I wasn't expecting a problem here.

*Drained the gas tank, and the carb bowls, and filled with new gas.  This was my last longshot, no change.

*I've recently (500miles, 6 weeks or so) dismantled cleaned and reassembled the carbs, they are in spectacular shape.

I've been checking everything I can think of, I may have missed something.  About a month ago I, ahem, very gently set the bike down sideways in the driveway by accident.  It didnt even hurt the mirrors, and its a gravel drive, AND it was fine for a 250mile round trip afterwards so I cannot imagine I hurt anything.  Bike was resting on the right side, which is generator cover, correct?

I am COMPLETELY stumped.  The battery is fine, the coils are fine, they are seeing 12V, but the spark is so weak it won't hardly run - my ability to troubleshoot electrical problems is barely functional at best, but this baffles me.  Problem is symmetrical, if I pull one plug wire it'll still run, just even worse.  Power is fine, ground is fine, plugs and coils are fine... what the hell is in the middle that could do this?  What changes that heavy throttle will keep it running?  Change which jets the carb is using?? Advance the ignition??

Please please please help.  I am at your mercy.  Thanks in advance.

[gs500Ant]

hi mate,im nooooooooooo expert but thought i might try to offer my 2 cents worth for you.

when you dropped the bike on the right side did the suzuki emblem come off?,if so did you ride it with the emblem (cover off for those 250 miles) i only say this as i to (ahem) dropped mine that side at about 1/8 mph but lost the emblem,shite got in there and damaged the pickup (right side) replaced the picups and a better spark.

also,take it you have tried spraying around the carbs,boots,air intake incase of any leak?

sorry this is all i can offer matey-  goodluck

Ant.

[Robzor]

I appreciate any input at this point friend 

I didn't hit it hard enough to hurt the emblem, but I may as well take the cover off and inspect the pickups.  If something's obviously bunged up in there that could do it... maybe the coils vary spark voltage based on the strength of the signal?? I'm really reaching here....

An air leak should make it run lean, not super rich, I'd think, but I can triple check everything is sound in this area.

[Robzor]

Bump/cry for pity.  Pickups at the right side of the engine case look fine.  Going to try running alligator clips to the coils from the battery, maybe the voltage is finding some other path to ground??

Any ideas, even bad or crazy ones...

[The Buddha]

Try the auxillary ground ... it could be bad, and heck you could also have bad spark plugs.
Cool.
Buddha.

[Robzor]

Try the auxillary ground ... it could be bad, and heck you could also have bad spark plugs.
Cool.
Buddha.

Thank you, I was looking for a reply by one of the forum gurus!

I've visually inspected the aux. ground and it looks clean and secure.  Where is a good place I can check its continuity?  Resistance to a +12v somewhere? At the voltage regulator??

Bad plugs, technically possible at this point but statistically unlikely - the old plugs operated exactly the same as new plugs, having 4 plugs simultaneously fail seems unlikely, new plugs was my first thought..

[simon79]

Where is a good place I can check its continuity?

Just a thought, I'd suggest checking resistance between the battery (-) pole and another point grabbing on the frame, e.g. one of the two bolts - under the passenger seat - holding the tail plastics to the frame. On my bike, its value is somewhere between 0.06-0.07 Ohms or something like that IIRC.
More significant values may mean that aux ground connection is bad.

[Robzor]

Ok, the aux. ground has good continuity to the battery (-) terminal at least.  I checked the resistance from the neg. terminal to the ground nut at the case yesterday and read something like 4 OHM, which seems a little high but could that really cause all this trouble?  I'll check to a few points on the frame..

[Robzor]

Nevermind, resistance to ground is good, pegs the multimeter at 0.