GS 450 idle gone crazy

[blackie_81]

Dear GS owners,

I wold like to ask for some info about my bike's strange behaviour. Well, I have a 1985 Gs 450 E, just bought it (the day before yesterday).
When the engine is cold, it runs fine, sounds fine and idles fine. But when it is warmed up the idle spins up to 3-4000 rpm and it goes back to normal very slowly (it takes about a minute, depends on the engine temperature - the warmer is the engine, the slower is the "slowin'-down").
By the way, what is that little thing under the carbs on this machines? Is it the camchain tensioner, or what?

Thank you in advance!

[Red_Phil]

The thing under the carbs is indeed the cam chain tensioner.

As for the raised idle speed.
I believe that is a symptom of a lean condition.
Possibly an air leak around one of the carb boots?

[IanFrancisco]

I had a similar problem that was due to the pilot screws being only 1 1/2 turns out and the throttle stop screw turned in too far to compensate. Your pilot screws may still be sealed. They are located on the sides of the carbs towards the top of the carbs and towards the front of the bike, ie near the intake boots. Some carbs were sealed with what looks like a miniature freeze plug. All this assumes you have the BS34 Mikunis (CV type). If your pilot screws are sealed, carefully drill out the plug to expose them. Then set them about 2 1/2 turns out from lightly seated. You will then have to back off the throttle stop screw, the big thumbscrew underneath and between the carbs, to get the idle to stabilize at around 1000-1100rpm. If this soesnt' work and you still have an unstable idle, a slide may be sticking or there may be a clog in the carbs somewhere. You can check for air leaks around the boots by spraying a fine water mist around them. If there's a leak the water will get sucked in and cause a hesitation or misfire.

[skip]

that is also a symptom of your carbs being out of sync. if you cant find a lean condition or vacum leak , try syncing your carbs

[IanFrancisco]

Carb syncing is fairly simple on these twins. Most of the time "bench-syncing" them is good enough and the merc stick method can be left for those of us who are more meticulous. To bench-sync you just need to make sure there is about .005 in. clearance under the butterflies when shut (feeler gauge) and that they shut at exactly the same time with the clicks in unison (sounding like one click rather than two). Fairly easy to do with only two carbs.

[jhw84]

I had a similar problem after I replaced a sunken float. It doesent hurt to check float heights.

[Billy Ricks]

You can run a two cylinder bike on one cylinder at a time to sync the carbs by just removing one plug wire at a time. Just raise the idle enough so it will run on one cylinder and adjust the carbs for mixture first then idle. One carb probably won't have an individual adjuster so start with it. Adjust the idle mixture screw for that carb until you get the highest, steadiest idle from that carb. Then go to the carb with the adjustable idle stop and adjust mixture first then set the idle to match the other cylinder. After you have both carbs set you'll have to drop the idle using the stop that controls both carbs.

[IanFrancisco]

I had a similar problem after I replaced a sunken float. It doesent hurt to check float heights.

Ditto. I had to raise the fuel level in the bowls slightly to richen up the midthrottle range as the needle wouldn't lift any more. I wish these BS34 carbs had old-school multiple grooves and a clip for the needles...