Just wondering if this is normal, but I only get about 15-20 miles per gallon AT THE VERY BEST. I usually hit reserve around 40-50 miles. I am pretty sure this is not normal. Anyone know WHY it would be doing this? It is a '95 model. It seems to run fine, I have recently had the carbs cleaned and replaced the coils. However, the left cylinder still has a VERY weak spark. At idle, you can completely remove the left spark plug wire, and NOTHING CHANGES. GASP!! Yet if you remove the right wire, it cuts off immediately. However, it seems that the left cylinder kicks in past about 4k rpms. Below that, no torque or power whatsoever. Yet it seems to have full power and torque past about 7k. It smells like gas after riding a few miles. Theories, anyone?

Fuel consumption should average around 50mpg, you have a major problem. I'd start by checking compression, then valve clearance. Sounds like you're losing compression on your left cylinder.

If I was losing compression, it would have to be either the valves or the rings, right? And if it was the rings it would smoke and use oil, right?

I'd check all the bases.  For a 4 stroke engine to work you need: Compression, Fuel, Air, and Spark.  Youre using plenty of gas, and air is probably not the problem....and you may have it nailed with the spark being weak.  But check the compression anyway, can't hurt.  Try moving the coils/wires from cylinder to cylinder and see if it moves with a particular component.

when i replaced the coils, i did swap them back and forth between the cylinders, and the problem did not shift with it. it stayed in the left cylinder.

I would start suspecting an ignition pick-up problem with a weak spark if it's not the coils.  The pre 04 GS500s have 2 pickups to trigger the spark under the small cover at the right side of the crank, one for each coil/cylinder. 

so are you saying to check for problems under the stator cover? I am not exactly a professional when it comes to motorcycle engines, I am an automotive mechanic, please bear with me. What exactly should I look for?

haha i just got a good laugh. I have a thread exactly the same as this one on stuntlife.com. the best response i have gotten over there is "fuel gremlins are stealing gas for white witch's sleigh". those guys are useless.      

Yeah, mine is averaging like 60 

Quote from: TurkeyChicken on June 21, 2009, 09:42:09 PM
Yeah, mine is averaging like 60 

you get more on one gallon than i do on an entire tank!?!? that just makes me wanna slap full coverage on it and run it off a cliff. . . . .

Jay Leno's jet bike gets 4-6 mph. I think you're getting seriously screwed on the MPG/Fun ratio if his bike is getting better MPG than you, and his bike makes jet noises at the same time.

Damn I want jet noises.  Maybe I can wire up a fake blow off valve to it?

I average about 49 MPG, so yeah, must be those gremlins.

The ignition pickups are under your fancy Dr.Pepper cap.  Since it's only running on one cylinder and you just had the carbs worked on, I'm leaning towards a carb sync.  Good luck.

A worn left cylinder or valves doesn't explain weak spark on the left cylinder.  Since you are getting a spark, however weak, your pulse generator is working.  The fuel in the left cylinder isn't burning.  That's why you smell it as you ride.  The first thing I would check in this situation is for corrosion on the spark plug wire where it connects to the coil.  If that's good, time to check your connections back to the ignition module.  Good luck.

I have the same symptom, plus it's fouling my left plug. Buddha turned me to the vacuum line, to try pinching that off and running the frame petcock on pri, w/e that stands for. Will report back with my findings when I can test ride.

I'm still thinking it's a fuel problem.  Since you state in your original post the engine seems to have full power above 7k rpm. That's when the jet needle and the main jets are in play.  If you take the airbox off and spray some ether/starter fluid into the left carb while at idle and it comes to life, I'd say sync the carbs.  Just my .02 as I had a very similar issue recently.

Let us know how it goes.

willing to bet, since it's a 95, your diaphragm in your frame petcock has gone bad, leaking fuel into the left cylinder and drowning it out.    Easy fix just switch out to the Honda dirtbike fuel tap as outlined in the wiki.....oh yeah hold onto your socks when your horsepower doubles as the left cylinder comes back on line.   

Whatever it says in my sig is waht i was averaging....until I meet up with the Ken and the Buddha.

Compression test FTW.  Why not rule out any compression issues since it takes 5 minutes to check it.