82 GS750T - Idle at 8000 RPM

[Shannon]

I have an 82 GS 750T and she starts right up and goes straight to 8k RPM and will NOT idle down... choke is OFF, fuel valve is in Prime position

Here is what I have done since I got the bike in June 2012:

1) New Battery
2) New Fuel Petcock
3) Removed and thoroughly cleaned all carbs (Dipped and used air and spray carb-cleaner to clean all passages and jets)
4) installed 4 carb rebuild kits ( All new jets and o-rings(viton))
5) set float heights to specs in Clymer Manual (22mm with vernier caliper)
6) replaced the fuel/air mix assembly and set all 4 to 2.5 turns out
7) bench synced all 4 carbs so that throttle plate is set exactly the same on all 4.
8) all intake boots are brand new, sealed and not cracked or leaking air
9) replaced Pod air filters with stock airbox (new boots where they connect to carbs) and new air filter.
10) brand new NGK spark plugs, properly gapped


I have removed and recleaned and re-synced the carbs twice now and the same results each time...

I did find a thread that mentioned even a small opening of the throttle plates could cause high RPM on idle, and my throttle plates are all synced with just a very slight gap... could this be the problem?

I also need to check if throttle cable is preventing them from closing completely, but I dont think that is the problem. i iwll verify.

Anyone have any suggestions?

the bike sounds strong, not back firing or sputtering or sensing any loss of power, it starts right up and just revs REALLY high, I dont let it run for more than a few seconds.

[loud et]

You should have no gap after bench sync. After sync you are supposed to unscrew the master idle all the way and then screw it back in until it just touches the idle plate. Then turn it in one or two full turns. At that point the throttle is slightly open, but not really enough to call them open (viusally) you will not really see much of a gap.
How wide are your plates opened as it sits?

[850 Combat]

As I recall, it is possible to hook up the throttle cable to the wrong hole in the hand throttle. Its possible that this happened to me on another bike. I'm assuming that yoy have turned the idle down all the way. I would confirm cable routing, and confirm that the cable housings are fully seated at both ends and at the adjuster if fitted.

[john82q]

I also need to check if throttle cable is preventing them from closing completely, but I dont think that is the problem.

but thats the first thing to check!
to be sure undo the cable at the carby end and see...

you have tried backing out the thottle stop?

[BigD_83]

Yes. Check this. If you have had the cable out of the throttle housing, it is possible for it to jump out of it's "track" taking up more tension that it should, and opening the well-synched butterflies well beyond where they are set on the bench.

[BassCliff]

Greetings and Salutations!!

Hi Mr. (Ms.?) Shannon,

You've put in a lot of great work on your machine already. Good show.

Aftermarket carb "rebuild kits" are known to be inferior and incomplete. OEM carb parts are expensive, but they are the best solution. A full O-ring set for all the carbs can be found at http://cycleorings.com.

Yes, check for proper cable installation and adjustment. Check for air leaks in the intake system. You'll find the proper recommended carb cleaning procedures on my little website.

For grins and giggles>>> New Members, CLICK HERE!!

Welcome to the forum.


Thank you for your indulgence,

BassCliff