uncontrolled high revs (and other weird symptoms)

[jboogie13]

Finally got my bike started tonight and it was acting stranger than any bike I've dealt with to date.

Bike:
89 gs500
Stock exhaust
Stock carb setup.
(supposedly) 11k on motor

Bike was sitting outside for around 2 years, but all electrical works.

The bike starts fine, but immediately revs up to 5-6k and hangs there regardless of choke/throttle/idle setting.

The exhaust gets extremely hot, i tried shooting with a temp gun, but it was out of range. (unsure of range on gun)

I removed left side plug boot and the revs dropped to 2k and seemed to respond to throttle.

replaced left boot, and removed right boot and the revs go backt o 5-6k with no response.

Fuel system seems to be in check (obviously not)
Could this be electrical related?(funky cdi box?)

I'm lost. I drained the oil and put fresh oil in to remove any washdown to no improvement, no more fuel in the oil though.

Any/all help is greatly appreciated.

[RossLH]

Vacuum leak, most likely. Spray some WD-40 around the carb boots and see if the RPM jumps up.

[jboogie13]

Vacuum leak, most likely. Spray some WD-40 around the carb boots and see if the RPM jumps up.

wouldn't it need a pretty serious leak to get that high? and are the stock carbs jetted that high that they will supply enough fuel to keep it from just dying?

I will give it a go, and hopefully that is the issue.

[Big Rich]

Something is out of whack with your left carb. What happens if you pull the right side spark plug boot?

Check for the leak as mentioned, but also float height, carb sync, sticky slide, etc.......specifically on the left side.

[jboogie13]

Something is out of whack with your left carb. What happens if you pull the right side spark plug boot?

Check for the leak as mentioned, but also float height, carb sync, sticky slide, etc.......specifically on the left side.

when I remove the right side boot, the revs stay the same.  I forget what i set the float height to, but what is the stock float height for these? For some reason 12mm sticks out in my head.

[The Buddha]

Something is out of whack with your left carb. What happens if you pull the right side spark plug boot?

Check for the leak as mentioned, but also float height, carb sync, sticky slide, etc.......specifically on the left side.

when I remove the right side boot, the revs stay the same.  I forget what i set the float height to, but what is the stock float height for these? For some reason 12mm sticks out in my head.

Its 14.7 or something ... I never figured out that method. I set em U tube method to top of the bowl.

Your high revs are not due to high or low float ... you're either sucking air, or super super super lean on the pilot and air screw circuit.

Cool.
Buddha.

[jboogie13]

The mixture screws still have the block off plugs in them from the factory, so i doubt its lean.

I will check for sticky slides, and vacuum leaks tonight.

[Soloratov]

It doesn't take much of a leak for it to go up. A pin hole in the right spot can take you up there real quick.

[jboogie13]

It doesn't take much of a leak for it to go up. A pin hole in the right spot can take you up there real quick.

so youre saying something like dry-rot on the intake boots could be doing this?

[Soloratov]

Oh absolutely. Cracks in the boots are the first thing you should be noticing. Replace them. All it takes is a pin hole to throw everything off.

[The Buddha]

The mixture screws still have the block off plugs in them from the factory, so i doubt its lean.

He he he ... that means its leaner than Lindsay Lohan ...

Cool.
Buddha.

[jboogie13]

Oh absolutely. Cracks in the boots are the first thing you should be noticing. Replace them. All it takes is a pin hole to throw everything off.

I didn't see any when putting the bike together, as the previous owner claimed the bike was running fairly recently.  Will look closer.

He he he ... that means its leaner than Lindsay Lohan ...

While i understand that the stock setup is relatively lean, I highly doubt that it would be so lean that it would cause this behavior on it own, with an all stock setup.

At any rate, do you recommend I adjust the mixture screws at this time?

[Soloratov]

Really, you should never need to adjust them. Do the spray test on the intake boots, and the throttle linkage that runs through both carbs. Chances are, it's just an air leak, which can be fixed easily.

[jboogie13]

Really, you should never need to adjust them. Do the spray test on the intake boots, and the throttle linkage that runs through both carbs. Chances are, it's just an air leak, which can be fixed easily.

yeah, i'm a fan of trying one fix at a time, and starting with the cheapest. It makes it easier to find the source.

thanks for allt he quick replies, I didn't expect this much activity so soon haha. 

[jboogie13]

did the spray test, no real jumps in engine speed, but i pulled the boots off, cleaned them, and replaced the o-rings. Everything on the carbs looked ok from a visual externally. Put everything back together and the same exact things happen, only when either spark plug boot is removed, the rpm's drop to 4k.



EDIT:

I took everything apart again, and opened the carbs up, everything looked alright, but i reset the floats to ~14.5mm just for shits and giggles.

Put everything back together and it idles great. Don't know what happened, but i feel that the throttle may have been sticking open?

It does however hang the idle at around 3k now. I am plugging the two large connections to the airbox (one on top, and one on bottom) because im willing to bet they are related?

Thanks for all the help everyone, really glad this got sorted!

[The Buddha]

Floats being higher will richen the bike, lower will lean it ... it affects all across the rev range.
I'd set floats to the top of the bowl ... no clue what that is as a number.

Open up the air screws, that 3K hang will probably go away.

Cool.
Buddha.

[Garrett]

Glad it got sorted.

Cool.
Garrett.

[jboogie13]

Floats being higher will richen the bike, lower will lean it ... it affects all across the rev range.
I'd set floats to the top of the bowl ... no clue what that is as a number.

Open up the air screws, that 3K hang will probably go away.

Cool.
Buddha.

so more fuel in the bowl(lower float height)= leaner mixture
less fuel in the bowl(higher float height)=richer

This always has confused me, but i have seemed to get by.
I will play around with the air screws if it gets any worse.

[RossLH]

so more fuel in the bowl(lower float height)= leaner mixture
less fuel in the bowl(higher float height)=richer

This always has confused me, but i have seemed to get by.
I will play around with the air screws if it gets any worse.

Float height is the distance between the gasket surface and the bottom edge of the float, which makes the term "float height" a bit counter intuitive as I've seen it used here. A higher float height means the float needle stops the flow of fuel when there's more distance between the gasket surface and the bottom edge of the float, so the float is actually lower, thus less fuel in the bowl.

[The Buddha]

Floats being higher will richen the bike, lower will lean it ... it affects all across the rev range.
I'd set floats to the top of the bowl ... no clue what that is as a number.

Open up the air screws, that 3K hang will probably go away.

Cool.
Buddha.

so more fuel in the bowl(lower float height)= leaner mixture
less fuel in the bowl(higher float height)=richer

This always has confused me, but i have seemed to get by.
I will play around with the air screws if it gets any worse.

No, Yea I hate the numbers for float height method - But - Higher the level in the bowl, richer.
Cool.
Buddha.