Topic: Bench syncing 73 cb350f carbs

[Coredozer19]

I know vacuumed sync is the best but I just want to get them close so I can get my idle in check. Any videos or advice on the subject?

[innovativems]

I use a 1/8 drill bit to bench sync mine


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[Coredozer19]

When bench syncing where do you set your idle adjustment screw

[Flyin900]

Download the FSM from the site and all the info is contained in there for your setup.

[Coredozer19]

I’m a noob what does FSM stand for.

[Flyin900]

Welcome noob!

Look under the manuals and tech section about four subjects down from the top on the Home Page. There are wonderful people who have taken the time to copy and load a complete Honda Factory Service Manual for your pleasure. (FSM)
You will find all the information on every facet of the bike including tune up and major and minor repair info.

[WhyNot2]

The 1/8th inch drill bit works great.

[Flyin900]

The factory spec is 1mm not 1/8 of an inch and so too large as FYI 1/8 " = 3mm.

If you are using a drill bit a .040 micro drill bit is the correct size for the 1 mm spec.

Back the idle adjuster off completely so it isn't affecting the slides you want the slides sitting in their resting position with no idle adjuster engaged.

[enwri]

When bench syncing where do you set your idle adjustment screw

Depends on what size drill bit you use, follow whatever the FSM says .

[Coredozer19]

Okay I have a clymer manual I wasn’t sure if it states how to bench sync carbs or not

[enwri]

As long as you can back off the idle speed adjuster enough to just close the throttles when you are finished. (if the guide doesn't say anything about it.)

[WhyNot2]

I benched synced mine a while ago, ran nice after, but I let it sit for a few years, brought it back to the front and now it pees all over the place.

Looks like carb removal is in the future again.

And they are a pain to remove and install.

[evinrude7]

use a paper clip stretched out.  follow this and you'll be fine.  http://www.hondachopper.com/garage/carb_info/bench_sync/bench_sync.html

[bochnak]

Here is a video on how to do it:

[bhh1989]

Trying to avoid starting yet another thread on this..  Been trying to piece together information from all these threads relevant to 350F only.

The FSM helps with other things to check but doesn't really walk you through bench syncing carbs.

Basically I followed directions, mounted carbs, bike idled super high. No air leaks. This was more tinkering around than final, I still need to do cam chain check, timing check and valve clearances but in the meantime...

The 1/8" drill bit vs. 1mm factory height thing concerns me - where is it stated the slide should be 1mm high (and thus 1/8" = 3mm drill bit would set the slides too high)?  I concur the may be the case for the CB350F as it caused my bike to have a very high idle even with no contact on the throttle adjustment bolt until I eventually lowered the slides with it ON the bike 1.5 turns in (down).  This of course wrecked my "close" bench sync and now I'm in no man's land and need to pull the carbs and restart.

However, I also came across another step in another thread where you should start the sync process by touching the throttle bolt to the tang, then turning it in 1 full rotation.  I did not do this, I had no contact on the tang until I mounted the carbs and then set it to just touching the tang.  Could that be the issue?

[caluser2000]

Any small drill bit will be fine. The important bit is all the slides are set at the same height and move up and down simultaneously.

[bryanj]

Go to sohc.co.uk
Go to tricks and tips
Go to page 2
7th down is a how to i wroteand 1/8 is way too big you need 1/16 or smaller ( 1mm or even less)

[bhh1989]

Go to sohc.co.uk
Go to tricks and tips
Go to page 2
7th down is a how to i wroteand 1/8 is way too big you need 1/16 or smaller ( 1mm or even less)

Awesome stuff, thank you.  I saw a video where a guy used a WD-40 straw.  I am going to measure that and see if it's about right.

[bryanj]

Too flexible, you need something that cant be crushed

[Deltarider]

Just peeked at 'Tricks and Tips' and I'm pleased to see Bryan suggests the same approach, I've practiced on my CB500, knowing: engine side. I've used a small allen key's long leg as a feeler gauge. You have to concentrate though and take your time. I've done it three times. When checked afterwards with a vac gauge set, it turned out I had managed to limit the difference within 2 cm Hg, which is well within factory specs. Some use steel balls to achieve a sync, by pursuing a simultaneous drop of the balls. I haven't tried that. It will be time consuming I guess, but should work.

[bhh1989]

I didn't see these replies until after redoing the bench sync with a WD-40 straw...  It measured 2mm in diameter, so I ran in the idle adjustment screw a little more to compensate then brought it back in to the full turn afterward.  Dialed it in, checked over and over the clearances with both no and full throttle and was pleased.  You definitely need to move the slides up and down after each minute adjustment and then check again - super easy to be off after tightening when talking about 1mm. I also set cam chain tensioner and valve clearances while carbs were off.

It absolutely purrs now.  Just a tiny blip of the starter when cold, no choke, and it starts and idles smoothly.  Still needs vacuum syncing (tiny tiny bit of hanging throttle once warm) but I am very happy with how the bench sync turned out.

Thanks folks!