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gs650 vacuum hose and idle screw trouble

  • Thread starter Thread starter n00ben7
  • Start date Start date
N

n00ben7

Guest
Edit: Fixed. Flooded engine and choke not adjusted properly. Thank you.

Hi guys,

1981 gs650glx with mikuni bs32ss carbs

Problem 1:

Having a hard time getting my bike to start with the vacuum hose attached to the #2 carb. My tank has 3 hose connections:
  • Main fuel line on the petcock
  • vacuum line on the petcock
  • near the float towards the front of the tank (this one is just a vent?)

When I first connected everything it ran fine with the vacuum line. Later when I tried again it would crank and want to start but wouldn't.

It started fine with the #2 vacuum disconnected. I did use a washer jet hose I found laying around since I didn't have a correct one atm. I tried on all 3 petcock positions with same result. Is this a petcock issue or the hose may have kinked? There is fuel in the main hose going to the carbs.

carbs.jpg


Problem 2:

I adjusted the throttle stop knew/knob when the bike was off. I lost track of the original position and I have a feeling I'm way off. Could this be causing starting issues or does this only control the idle rpm? Is there a way to adjust this by turning it all the way one side and X turns the other way? Can't find anything in the manual about this except to adjust it with the bike on to control the rpm.

The knob I'm talking about is referred to as the "throttle stop screw" in the manual. It's the bigger knob on the bottom side of the carbs between #2 and #3.

Thanks.
 
Last edited:
problem1..
My petcock has only two connections...one to supply fuel to carb and another to connect #2 carb vacuum nipple to petcock vacuum fitting (this is the smaller one)
the third hose is just a drain hose from fuel sender unit

?tried on all 3 petcock positions with same result.?

The ?PR? position should have let fuel flow . Review your connections

problem2
if you have the throttle stop screw way off..holding throttle plates too much open...you defeat the choke/enricher system, as this relies on closed throttle.
you should be able to feel when throttle stop screw is no longer holding plates open.
 
The knob big knob, use this to set your idle casually when the bike is warmed up. It's just about the LAST thing to adjust on a motorcycle.

But first, if you have been randomly adjusting elsewhere, double-check the one where your throttle cable connects to the throttle plates...there'll be some kind of instruction in your manual but ...in case it helps...set IT so the so your "reference"throttle butterfy can completely close.
it's best if the carbs have been "synched" but the main thing here is that you can see that the main throttle, plate-the "reference" throttle that the others are synched to-can "relax" on it's stop. This is so further adjustments can be made without the cable's adjustment interfering....

Next, on the bike, take all adjustments out of the throttle cable. Then, attach the cable. Then take excess slack from the cable using the nuts on the carb but you always want a bit of slack at the twistgrip and where the cable attaches to the carb too. The throttle must be able to "sit down" and relax on its rest. The cable must of course snap back when you release the grip too.

Routing the cable gets very important about here- test this by turning handlebars side to side! Make sure it isn't tweaking the throttle at the carbs!

Finally, you get to turn the big knob and adjust idle...:)
Start the bike with the choke/enricher and when the bike wants to run warm, and as you reduce the enrichment to none, set the big knob to idle around 1000 to 1200 rpm. Readjust when the bike is truly warm and happy...and finally-finally, the the throttle cable will gain slack as you turn the idle up,so take a bit out at the adjuster at the handlebar.not at the carbs ( sometimes,on some aftermarket cables there's another adjust place further down the cable housing a ways.)

again, check for correct, non-binding cable routing when you turn the handlebars. It's quite disconcerting in a parking lot if your bike accelerates when you turn the handlebars.

Petcock:The bike will not run well with the vacuum port on the carb unconnected to the petcock or otherwise "open" to the air.

Test the petcock vacuum function by sucking on the vacuum line. Fuel should flow. Test the Prime function- it doesn't need vacuum for fuel to flow and is used to top-up the carb bowls before starting when the bike has been sitting awhile. It can take a minute or more to fill 4 empty bowls.The bike can run on prime just fine, assuming the floats in the carbs are in good shape and don't allow the carbs to flood.
 
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