carbs not shutting off correctly

[andyp62]

hi
I have a 1978 GS 750 DB, I have just got it running again but there seems to be an issue with the carbs, from idle opening the throttle the engine revs highly and wont return to idle on closing the throttle, I tried new cables and removed the shaft through all four carbs to make sure no rust but still the same. If I open and close the throttle linkage by hand when the engine is off it snaps closed as it should, but with the engine running and not using the twist grip, just opening and closing the carbs results in the same sticking. Is there anything could affect the revs only when the engine is running ?. I don't understand why all seems ok when the engine is turned off.
Any advice gratefully received
Thanks

[tom203]

Might be the boot/o-ring at head interface see parts 16 and 17 in this layout. Old dried up o-rings let excess air slip in giving you a high unstable idle

http://www.partsoutlaw.com/oemparts/a/suz/50d3ff0bf8700230d8b4dd97/air-cleaner

[Nessism]

Yup. Airleak through the boots is one of the most common issues with these bikes. Feel free to check the Newbie Mistakes thread link in my signature for a list of other common issues.

[tom203]

Have a look here

http://www.cycleorings.com/intake.html

[andyp62]

o rings

Have a look here

http://www.cycleorings.com/intake.html

thanks I will have a look

[andyp62]

thanks for that

[Steve]

You do have both cables connected?

.

[hannibal]

Don't forget to grease the shaft as well.

[andyp62]

hi Steve, yes both cables are connected

[andyp62]

will check on that

[Renovator1964]

i had the exact same problem last week and i had 2 broken tips from my pilot fuel screws in carbs 1 and 2, so pull your pilot screws out and see if tips are broke off in that little tiny hole in the throat of carb, my screws are on the bottom front of carb( Mukini VM 26's). there is a thread on how to get them out somewhere on this site. I took micro screwdriver and ground it down to about .37"bent it to 90 degree angle then took a heat gun and heated the carb to expand the metal where you can't touch it, put it in that little hole on the bottom part of the carb throat and pushed it out. if won't come out push down on top of micro screw driver with another big screwdriver. good luck

[andyp62]

thanks I will look at that