Topic: Where should the idle set screw be at on bench sync?

[khardrunner14]

Working through the carbs again and I've looked through the FAQ and searched. This is a k1 cb750. I've read something about 1/16th inch of "play", I read "close it down", and other stuff but I don't understand what that means. I might just be dull between the ears, but does it make sense to sync them with the adjuster screw all the way off of the bar that lifts the slides? If not, how do I know (starting from scratch) that it's in the right place?

[OldSchool_IsCool]

I've only worked with carbs on later year models, but basically, use the idle speed screw to set a reference carb (say #2) then adjust the other 3 slides to match.

So if you are using the 1/8th inch drill bit method, you would use the idle speed screw to close the #2 slider until it barely touched the bit laying flat in the throat of the carb, then adjust the other sliders to barely touch using the individual height adjusters.

Similarly with the flashlight method, place the flashlight in the intake throat of #2, close the idle speed screw til the light fades to zero on the output side, then move the flashlight to the next carb and make the light fade to zero with the adjusters.

[khardrunner14]

That helps but I'm still missing something.

I'm basically starting from scratch. They are so messed up now that I don't have any reference to start. RIght now it's set it the screw all the way off so that each carb barely fits a 1/8 bit through.

Is that alright or do I need to have it set with the Idle Screw on the arm already?

[OldSchool_IsCool]

I'm hoping a more experienced "Carbie" will step up with the real answer, but it makes sense to me that you should be able to completely close the slides with the idle speed screw.  If you have backed off the idle speed screw all the way and the slides still have a gap, then your slides are adjusted too high.

that's one reason I like the flashlight method over the drill bit.  The act of syncing also affirms that the sliders will close 100%

Again, I hope a REAL Carbie steps up to correct/affirm my assumptions.

[mycb750k6]

If I had responded to your post I might have been a little taken back  by your response. Folks are just trying to help and the FAQs do have a great deal on carb adjustments as does the rest of the site.

[khardrunner14]

Sorry, I'm not trying to take anyone back anywhere  . I'm just trying to give the most up to date info as possible. I do appreciate everyone's help and ideas!

[D-Ral]

I've only worked with carbs on later year models, but basically, use the idle speed screw to set a reference carb (say #2) then adjust the other 3 slides to match.

So if you are using the 1/8th inch drill bit method, you would use the idle speed screw to close the #2 slider until it barely touched the bit laying flat in the throat of the carb, then adjust the other sliders to barely touch using the individual height adjusters.

Similarly with the flashlight method, place the flashlight in the intake throat of #2, close the idle speed screw til the light fades to zero on the output side, then move the flashlight to the next carb and make the light fade to zero with the adjusters.

I've been rebuilding my carbs for the first time, and I have been following the instructions over at salocal.com. Everything has been great except I've found his bench sync instructions hard to follow. Makes sense now! Thanks!

[flybox1]

turn your idle set screw in until the #2 carb slide is raised.  insert a 1/8" bit.
back the idle screw out until the slide of #2 just barely touches the bit.
DO NOT TOUCH the idle screw after this.
set your other slides down on the bit from here....
done

[tomkimberly]

If you have completly dis-assembled your carbs, then set the idle screw adjustment to two (2) turns in. Set the height of the #2 carb slide to 1/8" gap. Check that the # 2 carb slide will close all the way by turning the idle screw back out. If OK, then turn the idle screw back in until you again get 1/8" gap and set the other three (3) carb slides to the same 1/8" gap.

Clear as mud....     


Tom

[lucky]

I'm hoping a more experienced "Carbie" will step up with the real answer, but it makes sense to me that you should be able to completely close the slides with the idle speed screw.  If you have backed off the idle speed screw all the way and the slides still have a gap, then your slides are adjusted too high.

that's one reason I like the flashlight method over the drill bit.  The act of syncing also affirms that the sliders will close 100%

Again, I hope a REAL Carbie steps up to correct/affirm my assumptions.

The idle screws should all be set at the factory setting to start. ONE turn out.
The slides should be bottomed out.
The curved cut out in the slides provides the air for idle.
Make sure that when the throttle starts to open (lifter arms move up) that all 4 slides start to move at the same time. Very important.

Thats it.

Read your workshop manual and follow the instructions.