Hi!  This is my first post about my first bike so please be gentle! 

Intro - skip for actual thread-related issue

I've just bought a 1999 GS500 with about 12k mi on it.  PO took good care of the bike but decided it was finally time to let the thing go due to space in the garage.  It's been in one crash but most of the minor cosmetic damage was dealt with pre-sale (and what was left, like a choke control box, is being replaced by me via ebay).  The bike is easy to ride and easy to learn on. 

I've been on two wheels since I was a kid, whether it be little 125 dirtbikes or bicycles or scooters or gopeds.  However, riding in the streets with a street-legal motorcycle leaves a lot to be learned. SO I've picked up most of my gear and I'm ready to start learning for my MSF course.

Issues

1) Starting idle issue

When starting the motor cold with the choke on, it'll warm up right up until the 2nd minute or so of warm-up.  After a minute or two of letting the idle sit, the motor builds revs... FAST.  I've let it rev up to about 6-7k when I hit the killswitch.  Starting it back up with the choke on or off lets the motor idle regularly.

I'm guessing vacuum leak?  I've never dealt with carburetors but from what I've searched and read about in similar threads, seems like I needa yank the tank and spray some WD40 around the carb intake tubes to see what bogs it down?

2) Warm idle bogging issues - Video below, sound kinda sucks.  It was parked up against my garage door when I recorded it with my cellphone so there's a lot of distortion but the gist is there.



This occurs once the motor's warmed up and I've ridden around town for a few minutes.  When I come up to a stoplight, it'll bog down and sound like it's hiccuping.  I also see the cables coming out of the right handlebar controls shake when it bogs.  Not sure if that means anything.  I don't notice any loss in power or anything else, just this annoying bogging at the stoplight.


Outside of that, bike runs great! Having a blast on the road! Just trying to take care of some bugs with this thing.

the bogging can be a few things...

petcock issues or your bike is airlocking somewhere.

that or your carb boots got an airleak somewhere.

also it may be your diaphragms, one might have a hole in it.

The cables probably are shaking due to the vibration?  You've got throttle cable, brake line, brake signal wires, run/off wires.  It seems like those would be unrelated to your uneven idle/hiccup thing.


Unless the hiccup is rapidly changing the angle of the butterfly valve in the carb, that might make the throttle cable move.  Don't know, I'm curious to know what the solution is.

I just realized I typed "clutch" every time I meant "choke" haha.

I'll be checking airleaks this weekend.

Watched video, the hickup is clearly the the sound fuel/air mixture lighting off in the intake, that condition is caused by being lean or the intake valve clearance is too tight or the valve is leaking. Put your hand on the Airbox, you will feel it "pulse" every time it hickups. The fuel/air mixture is lighting off on the wrong side of the intake valve.

Hmmm, how would one remedy this issue? Google?

Quote from: furiousbob on November 08, 2014, 09:11:50 AM
Hmmm, how would one remedy this issue? Google?

People here have had the "hickup" go away by simply opening up the idle mixture screw, not sure how being lean causes the phenomena...but it is more than likely the culprit 

Fuel To Air Mixture Is Too Lean
"Too much air and not enough fuel causes backfires to occur in the intake manifold. The exploding mixture then vents through the carburetor. Improper carburetor adjustments or vacuum leaks can cause this condition."

http://www.ehow.com/facts_7980825_carburetor-popping.html

Edited: nevermind

You guys are gunna laugh when you hear this.

I go out to my garage yesterday to start poking around my carburetor and noticed that my air filter wasn't seated. Matter of fact, the second I touched it (k&n lunch box), it fell right off the intake inlet. So I wrenched with it to squeeze it back on and started her up. Runs fine now! No more hiccuping. I still have the issue of the rpms shooting up once warm, however. I think I just need to read up on that, there seems to be a number of threads on them already.

If it wasn't rejetted properly after the air filter was installed, it's running lean. Any idea on jet sizes? If not, you might as well take the carbs off, give them a good cleaning, and pop in some new jets.

Also, since your carbs are off and it's apart, why not check the valves, too? No time like the present to show your new bike some love!

^ Gotta agree... check those valve clearances. I've been dealing with the hanging idle/rev issue. If your idle is set to about 1200 (or even higher) and your bike wants to jump up to 4k or more, it could be that the valves aren't getting the proper clearance. I checked throttle cable, good; looked for leaks, good; checked the carbs, good; checked the valves, bad. Exhaust valves were rubbing on the shims. Most people recommend checking it every 4k miles or so. I'm planning on going with a wider gap (closer to .08mm than .03mm) just so I won't have to change it as often. Now I'm just waiting for the shims to come in so I can see if that will remedy the situation. Since you've got everything else pretty much out of the way, might as well check em while you can.