After just buying a 1999 GS500E I have found a wide open throttle at about 6000-7000 i feel a strong misfire and a loss of power but when I close the throttle a bit the bike accelrates past the rpms and again i can WOT it and it makes tuns of power till about 9500 rpm where it agains misfires and loses power. Shifting to the next gear the whole scenario repeats. I have found that the faster I go the lower the rpms are when this occurs. I did find that the spark plugs hat the previous owner installed where about finger tight, must not have noticed that on the back of NGK spark plug boxes they show that the tapered seal plugs take an 1/8turn and not noticed that gasket type use a 1/2 turn to seal properly, besides the point. The misfire was reduced when I did that but it still remains. The bike has 11341 miles on it and the owner said that the valve lash was done at 8000 miles or so. Could it just needs to be reshimed or is there a carb problem?
If it were a valve problem, I think it would run wierd all over not just a high rpm. Same goes with a leaky carb or something. Could be a jetting issue. Maybe running lean or rich at WOT.
What kind of pipe does it have? Any rejetting?
Have you tried going up the gears at less than WOT like at say 3/4 or so?
Yeah thats the weird thing is it only does it at WOT, when i roll of the gas to about 3/4 throrttle it continues to increase in RPMs, its completly stock as far as I know. The owner said the only not suzuki part on the bike is the aftermarket seat, which i replaced with the stock(looks much better). When I pulled the plugs there were a whiteish tan color, more white than tan. As far as I can remeber whitesh tan is good, but i could be wrong, not carbon deposits or oily residue. Weird eh?
coll0412, sounds like you have a lean condition under WOT. Lean mis-fires usually sound like a real mis-fire (popping, banging, bucking) whereas a rich mis-fire is just generally sluggish and makes the motor feel lethargic. Your slides may be opening too fast or you may have a leak between the carb(s) and head. I'm really not that up on C-V carbs, so if the slides open too quick I am not sure what the cause would be. But if your plugs are white then, yeh, lean mis-fire. Next time it does it, chop the engine (pull the clutch and kill the motor), and coast in and pull the plugs. That will tell you a lot right there. Gotta love the little cycle and the forum too.
C.......
Normally flat-spots are generated by carb/exhaust issues. Potentially it could be fuel delivery, but it generally wouldn't hit only in one portion of the rev range.
Is the exhaust all rusty? Could be some sort of constriction there (I have one right now, which means I'm putting an aftermarket pipe on) that is causing a flat spot at that sort of RPM. However, my pipe is rusty and tapping on it give rattles that indicate a baffle has become dislodged, messing things up. There also seems to be a pin-hole leak near the front :( (I've just been informed this leak is supposed to be there! You learn something new every day - I love this forum!) Oh well, with a new canister I can help disguise the fact the bike ahs been dropped :)
Otherwise you can follow the instructions on the site to synchronise your carbs and see if that helps sort out the problem.
And for fuel, considering the vintage of the bike (not old) see if there are any kinks in the fuel lines that may just be messing things up enough that at WOT you aren't getting enough fuel. I've found in these situations it only happens at high speed and backing off doesn't help too much unless you really back off. Quick test could be to put the petcock on PRI and see if it cures the problem.