Topic: Where are the sync screws on Keihin PC 46A carbs?

[cmyoch]

Hello, first post here. I took on the project of rebuilding the carbs off my brother's 77 cb550. I searched the web, searched youtube, etc and found some tutorials and videos but I've noticed that the carb set I'm working on looks a little different on top. Where some photos and videos show the sync screws between carbs 1-2 and 3-4 for adjusting while the bike is running, this particular set does not have those screws. I know you can bench sync the set by adjusting the set screws above the slides but how do adjust them while the bike is running??  Any help with possible photos?

[lucky]

You need to get a shop manual.

Seriously.

When you sync carbs what your are doing is adjusting the height of the carb slides. This is a nut or screw with locking nut.

Except with the CB750 1969-70 it is an actual screw with a knob.

[Bankerdanny]

It's under the cap at the top of the carb. the #2 carb is non adjustable, so you will only find the screws under the 1,3 and 4.

The process is partially detailed in the factory repair manual you can download here at the forum, unfortunately there is a page missing from the section that details the synch process on the 77-78 CB550K's.

[Scott S]

 In this picture, it is NOT, I repeat, NOT the screw I'm pointing to with the screw driver. It's the slotted screw with the lock nut on it just above that in the pic.
 The #2 carb is not adjustable. Don't even take that carb top off. Hook up your gauges and get the other three to match #2.

[cmyoch]

Yes, I downloaded the shop manual and read through it noticing that, of course, the one page I need is missing. I know I bench sync using the set screws under the caps but where do I adjust while the bike is running? Do I simply rely on bench sync alone? Or, will the bike even run with the caps off? That was a dumb question but I thought I'd ask.

On my Yamaha XS650 and my GL1000, both have an adjuster held by a lock nut. Very simple to set using my homemade manometer.

[DGA]

Same screw, running or not.  Bench gets it in the ball park, vacuum gauges while running gets it home.

[cmyoch]

Perfect! This is what I'm looking for! I can't believe the bike will run with the caps off. Although I guess that's the difference with mechanical slides.

Thanks so much!

[crazypj]

CV carbs will run at idle with the slides completely removed, the throttle plate controls air (try it sometime, make sure you have an audience though, really freaks people out when you pull slide from running motor  )

[lucky]

Perfect! This is what I'm looking for! I can't believe the bike will run with the caps off. Although I guess that's the difference with mechanical slides.

Thanks so much!

The idle is controlled by the idle jet and mixture screw.
That is why a slide can be pulled out of the vacuum operated carb and it will keep running.

The slide controls the needle starting at 1/4 throttle.