Sporadic sluggish throttle

[mongreloctopus]

Greetings,
I am a complete noob so I apologize in advance for not knowing what I'm talking about.

I bought a '97 GS500e last summer, rode it daily until it started raining a lot this past winter and I'd ride it about once a week--probably about 10-15 miles each day max.  As it got colder (~30-40 degrees at night) it got harder to start in the morning, which didn't really surprise.  What I started to notice, however, is that about eighty percent of the time the bike was noticeably sluggish.  This would continue throughout the entire duration of each trip, and after I had warmed the bike for about ten minutes.

The position of the choke doesn't seem to make any difference--in fact, it seems like the choke is only operating in two positions, one which idles at ~1k and one which idles at 4-5k.  Opening the throttle 1/4 of the way maxes out my acceleration.  Anything above 1/4 only increases engine RPM at the same rate as 1/4...and despite the engine being at 8-9k, the bike is still accelerating as if the throttle were mostly closed.  As the RPMs rise, the engine sounds louder but I can hear a deeper resonant rumble that increases with engine speed.

Twenty percent of the time, when the bike is behaving normally, opening the throttle will send the bike flying as I would expect, and there is no deeper rumble that I can hear.

I haven't inspected anything on the bike except the oil because I don't really know what I'm doing...but I'm confident I can figure it out and fix it with some guidance.

Any help is much appreciated!

[Big Rich]

How often do you get gas? Sounds to me like your carbs might need cleaned.

[Mechmech]

On my first bike I had a similar problem (working throttle for a while, then the throttle would work up to about 1/3rd then the other 2/3rds were ignored). Turned out to be a combination of a faulty petcock and a bad vacuum line (the petcock created a constant problem, the vacuum line would only act up after the bike was warmed up... They worked in tandem to drive me insane for a while).

Have you tried changing your petcock setting to prime and seeing if the problem persists?

I'd suggest looking at your lines and checking them for leaks (run the bike, spray carb cleaner or wd40 on the line, if the bike makes a different sound you've got a leak there).

Could the engine sound just be the normal sound it makes at higher revs? Could you take a recording/video and post it to youtube for us to hear?

Like Rich said it could be the carbs... Pouring some seafoam into the tank and running the bike might help, from my limited experience.

[mongreloctopus]

How often do you get gas? Sounds to me like your carbs might need cleaned.

It's about once a week...this reminds me, though, that whereas before I was getting about 100 miles to a tank I'm now getting anywhere from 60-80.  Is there a way to clean them without disassembly, e.g. seafoam as recommended below?

Have you tried changing your petcock setting to prime and seeing if the problem persists?

I noticed early on that the petcock was problematic on the freeway, behaving as if it were out of gas...as a result, I ride around with the petcock set to prime about half the time I'm riding, depending on whether it's going to be streets only or freeway also.  There doesn't seem to be any difference between the two with regard to the problem I'm having.

I'd suggest looking at your lines and checking them for leaks (run the bike, spray carb cleaner or wd40 on the line, if the bike makes a different sound you've got a leak there).

Is the line you're talking about coming off the petcock and running toward the front of the bike?

I can try to take video, though I doubt the audio would be clear enough to hear what I'm describing...it's pretty subtle.  It's kind of similar to the sound of an engine in too high a gear for the speed of the vehicle--but in this case, the engine is already at 8-9k.

[jacob92icu]

The lines he is talking about that might be leaking are your gas lines coming from the gas tank to the petcock, then from the petcock to the carbs. Where he is saying to spray wd40 or carb cleaner is on your carb boots, which are the rubber things that connect the carbs to the head. If you hear a change in rpm when you spray carb cleaner or wd40 on it, then you have a vacum leak and should replace your boots. Easy fix.

[oz353]

This problem sounds very familiar.... I had very similar issues. I second the suggestion to check your Carb boots thoroughly ....can't stress that enough. I thought mine were fine when in fact they we're leaking.  If they are leaking do not try to repair the original boots. Replace them. Also I had issues with wind gusts, this I solved by routing my vent tubes well away from the wind. I tucked mine down in to the battery tray. I think I had to lengthen something...ah yes, the tube from the  valve cover to the airbox. I installed a k&n lunchbox air filter rejetted and made my own exhaust.