Topic: 350F Bench Sync question

[Lou]

Hi, when you do a bench sync on the carbs of a '73 350F, how far up should the slides be? I did mine using skinny drill bits (9/64") and now the bike is hard to start and doesn't want to idle when I open the choke. I did the bench sync with the return spring attached.

In the attached pic, a thicker bit is used so I think the slides will be farther open when idling. My 2nd question: when the throttle is at idle position (return spring pulled back to idle), how far open should the slides be?

Thanks!

[bryanj]

The slides should touch bottom if you wind the tickover screw all the way out, i usually say a 1/8 drill maximum so yours aint that skinny.
I would mack sure all slides touch then wind in tickover till one slide acepts small drill and adjust others to suit

[Flyin900]

Way too much opening there on the slides in your picture. The slides should be closed with the idle adjuster wound out as Bryan noted. Then adjust to a 1mm opening, so just slightly open on each one.

If you can do a vacuum sync afterwards it adjusts the carbs at idle to the motors peculiarities and differences in compression on each cylinder.

[Lou]

Thanks @Flyin900 and @bryanj. I appreciate the tips. I'm going to take the carbs off and do the bench synch as you said.

[newday777]

Thanks @Flyin900 and @bryanj. I appreciate the tips. I'm going to take the carbs off and do the bench synch as you said.

Keep this updated as you go

[Lou]

As I understand it, when starting to do a bench synch, the slides need to be all the way down (touching bottom) with the idle screw is wound out all the way.

I pulled the carbs off and tried adjusting the slides lower with the idle screw wound out and not touching. I adjusted the "slide adjuster screws" as far down as they would go but they are still not down all the way. Using a small drill bit as a feeler gauge, I'd say they are still open 3mm to 5mm (different on each carb). Attached pic #1 shows this. Pic #2 shows the idle screw is out all the way.

I tried some things to try to get the slides to adjust lower: Pic #3 shows the accelerator spring is detached (thought this might help but didn't). I pulled the nuts off the slide adjusters and also thin metal holder that connects the slides (one on the 2 left carbs and one on the 2 right carbs. These parts are in the magnetic parts tray shown in the upper left of pic #3.

I also tried loosening the 2 bolts at the top of the accelerator assembly (pic #3) but that didn't allow me to adjust the slides either.

Any advice on how I can get the slides to lower to a closed position? Thanks!

[Bodi]

confirm that the choke throttle advance cam isn't limiting slide travel. Once you change the balance screws the relationship to that cam changes.
I can't think of anything else. But something is stopping them from dropping. That cam acts on the main shaft, which is clearly not rotating fully.
Why take the spring off?

[WhyNot2]

Currently rebuilding carbs also. Just responding to keep up on your process.

Seems, mine are being a pain in the azz.

[Lou]

Will do. I played around with the choke and still unable to get the slides to lower so I'm dropping by a shop and have a guy look at it. I'll keep you posted.

[Floshenbarnical]

Before you do that, pull your emulsion tubes and examine them. If they're warped slightly, the slides will not close because the needle gets stuck. This was my problem with my PD carbs. I replaced all the emulsion tubes and they all dropped into place. Just make sure your needle isn't damaged as a result.

[Lou]

It turned out that I was adjusting the slides incorrectly. I was trying to lower them one at a time but that doesn't work. They need to be moved together and then they will do what you want. yep, still learning a lot!

[HondaMan]

Yep, the CB350F and CB400F carbs will teach their rebuilders quite a few new things that won't be soon forgotten!