High idle RPM, carb overflow, etc. remedied

[cchocjr]

Howdy all,
Just writing to catalogue my success at getting rid of my high idle (that wouldn't go down unless I let out the clutch in gear) and, following this, my overflowing carbs and 'prime only' running condition.

Some friends and I took apart my '89 GS500E to get to the carbs. We opened them up, cleaned them out with carb cleaner, and rejetted them according to stock specifications. They noticed that the various o-rings in the carbs were quite old and dried up. We hypothesized that this was inhibiting proper cut-off of fuel. These were replaced with o-rings obtained from a local NAPA store--much better seal.

Before this, we fiddled with the idle screw, and could get a decent idle for a minute or two, but eventually it would cut our fly up because of using the idle screw to overcompensate for a carb problem. We also checked out the throttle cable on handlebar end (though not the engine end--this is important, as I later came to believe that a stuck throttle cable was partially to blame for high RPMs at idle, though I don't regret cleaning out the carbs--they needed it.

After we put everything back together, it ran great...in prime, but would no longer run in 'on.' After reading many posts on the forum, I gave up, and decided that I would just run the bike in prime, but turn the petcock to 'on' when parked. I gave up on this after a few times of forgetting, and coming back after a few hours to a flooded bike hovering over an ever-increasing pool of leaking gasoline.

I planned on replacing the vacuum-system with a straight-forward pingel petcock, but first I wanted to replace the aged fuel line. I bought about 8 feet of quality 5/16 ID line (froma motorcycle shot) and a about 8 variable fuel hose clamps (screw-type, from Advance Auto Parts), and proceeded to rebuild the system.

It turns out that, when my friends and I took about the fuel lines when getting to the carbs, we failed to put them back properly. In particular, the vacuum hose was not going to the right side of the left carb, which would explain (duh!) the non-functioning 'on' vacuum system.

I got all of the new lines on just fine--though I did reuse the vacuum hose because of its smaller diameter--as well as the new hose clamps. Everything was nice and tight. I also took this opportunity to leave myself a little slack in the lines going to the tank petcock for easier removal of the tank.

Verdict: It runs great now! Carbs were dirty, and cleaning them helped for sure. Redoing the fuel lines wasn't necessary, but now I have new lines that are slightly larger, definitely better quality, and the experience and satisfaction that come from DIY work. After I got everything back together, the idle was spiking when I twisted the handlebars to one side--this turned out to be caused by the engine side throttle screw-thingy. In hindsight, this might have been a major culprit in the original problem.

Just sharing this to help out and to give hope.

\cchocjr

[xtalman]

I had a similar experience.  My bike would stall when coming to a stop.  If I was on an incline when stopped, it would idle just fine, but if I was on level ground, it would die.  I thought it was the float level but when I checked and re-checked they were fine.

I ended up replacing the fuel lines with clear hose, installing a fuel filter, cleaning the carbs, lubricating the choke cable, and replacing the frame-mounted petcock.  When I looked at the carbs, I saw some idiot had run the vacuum hose from the port on the left carb to the one on the right carb!  No wonder it would never run in "ON"!  I probably didn't need a new petcock.

I then ran the hose from the left carb to the petcock and now it runs fine in ON.  I have yet to test it for fuel starvation at high speeds, but I will get to it soon.

I don't know what actually fixed the problem, but I don't really care now either.  My bike runs great  

[CO_GS500]

Glad to hear of your success!

I'd be grateful for any members guidance on the probably related issue.

My '02 (3,800mi) basically runs great, but it's lately developed a way of coming off of RPM's sloooooowly.  So slowly that upshifts always jerk because the RPMs have not dropped suffeciently to match engine speed to the trans input shaft with the higher gear.

I've noticed this behavior before when the choke is on, so an over-rich condition is possible.  I've never had the carbs off or otherwise messed with them, only tweaked the idle speed as nec from time to time.

++Is internal carb wear likely at this age/mileage?
++Is it likely that the floats got themselves out of whack?
++Could the choke be stuck and not fully closing?

I'll check a plug tonight.

Many thanks,

Galen

[cchocjr]

Have you tried taking a peek at your spark plugs to see if they are carbon-fouled?

P.S. I also replaced the aged air filter in my GS with a mid-grade UNI filter, as my Haynes manual said that one of the problems that can cause one to end up with fouled plugs is a old/dirty air filter.

\cchocjr

[CO_GS500]

Yep, just checked both plugs and they look great- light tan/grey, no suggestion of carbon fouling.  The outermost threads of each plug, however, do show very light carbon build-up.

With dual-action throttle cables it seems unlikely that the throttles are simply not snapping shut as they should.

I've had some of that fuel system cleaner stuff in the tank recently, but I've refilled the tank since.  Does that stuff make for a richer mixture (is a greater volume of air required to burn the same volume of gas with that stuff vs. gas alone)?

Could out of synch carbs cause this behavior?

Thanks,

Galen