'90 GS500E Running Bad...Need Your Input

[SpeedProp]

Hi All....I'm new to the list and have recently purchased a '90 GS. The bike is really clean with low miles, but it's not running like it should. It has 7200 miles on it, starts easy, handles great, and is fun to ride. I've ridden other GS' in the past, and mine doesn't accelerate like or have the top end of others I've ridden. It doesn't misfire and I've checked the coil output, changed plugs, checked float levels, and compression. Everything is within spec. It had a K&N filter on it when purchased, so I removed that and put the stock airbox back on it. I haven't had a chance to test yet with the stock airbox, but am doing so today. Years back, I had a '84 Shadow and removed the stock filter and replaced with a K&N filter. The thing wouldn't hardly run due to the K&N flowing more air than stock and leaning down the mixture. On the GS, does using a K&N filter require a jet change? Also, is there a way to check the fuel pressure out of the fuel pump? I know the fuel pump works off vacuum, but when I take the tank off and turn the tank valve on, fuel dribbles out, instead of flowing freely. I took the tank valve out of the tank and the screen is clean. Do the tank valves normally flow this miniscule amount, or can I expect a healthy flow?
Acceleration feels like the engine is starving for fuel and you can hear an occassional bog, and every so often, you can feel the engine pick up like it's getting the required fuel and it accelerates briskly like a GS should.
Put your thinking caps on and shoot me some feedback please. I have much wrenching experience and have rebuilt several motors, so be as techy as you like.
Thanks.
Speed

[The Buddha]

You got somehting in your tank blocking it from flowing.l I would guess rust, but your clean tank screen rules it out. My second guess is, bad tank vent or a coating on the tank that has come loose and is blocking stuff from flowing. Do not laugh, I found a piece like that in this clown's tank. Kreem or POR 15 or whatever that is used to coat has to be just thin enough to coat it and not be used to fill up large sections of the tank (in this case the crap pockets) That's all I can guess at this point.
Yea fuel is gravity flow, no pressure and we dont ahve fuel pump - vacuum or not.
Cool.
Buddha.

[ben2go]

Hi All....I'm new to the list and have recently purchased a '90 GS. The bike is really clean with low miles, but it's not running like it should. It has 7200 miles on it, starts easy, handles great, and is fun to ride. I've ridden other GS' in the past, and mine doesn't accelerate like or have the top end of others I've ridden. It doesn't misfire and I've checked the coil output, changed plugs, checked float levels, and compression. Everything is within spec. It had a K&N filter on it when purchased, so I removed that and put the stock airbox back on it. I haven't had a chance to test yet with the stock airbox, but am doing so today. Years back, I had a '84 Shadow and removed the stock filter and replaced with a K&N filter. The thing wouldn't hardly run due to the K&N flowing more air than stock and leaning down the mixture. On the GS, does using a K&N filter require a jet change? Also, is there a way to check the fuel pressure out of the fuel pump? I know the fuel pump works off vacuum, but when I take the tank off and turn the tank valve on, fuel dribbles out, instead of flowing freely. I took the tank valve out of the tank and the screen is clean. Do the tank valves normally flow this miniscule amount, or can I expect a healthy flow?
Acceleration feels like the engine is starving for fuel and you can hear an occassional bog, and every so often, you can feel the engine pick up like it's getting the required fuel and it accelerates briskly like a GS should.
Put your thinking caps on and shoot me some feedback please. I have much wrenching experience and have rebuilt several motors, so be as techy as you like.
Thanks.
Speed

Any time you change the exhaust or air filter you have to rejet.The frame mounted petcock works off engine vacuum and may be bad.Here is some links to fix that.

NO FUEL PUMP ON THE GS.NONE EVER ON ANY YEAR.

Jetting how to's.
http://gstwin.com/rejet.htm

http://cgi.stanford.edu/~sanjayd/gs500/Upgrades/Rejetting

http://cgi.stanford.edu/~sanjayd/gs500/Upgrades/Rejetting-LeanOrRich?


How to eliminate the vacuum operation.
http://gstwins.com/gsboard/index.php?topic=19363.0

Cheap replacement.
http://gstwins.com/gsboard/index.php?topic=36958.0