Author Topic: CB550 Bench Sync Procedure help (Read 8154 times)

Fraserimoore · « **on:** July 08, 2016, 07:44:25 AM »

Hi Guys,

Please don't shoot me...I'm sure this is a much talked about topic, but simply, I cant seem to find the answer I'm looking for, even after trawling through the various threads.

I've recently rebuilt my carbs (022A's) and they look very nice indeed, but before I put them back onto my CB550K1 I would like to bench sync them.

With your wisdom can you please confirm the procedure to correctly bench sync.

I've seen many videos where people are simply adjusting the butterfly valves?

Should I not be adjusting the slides also?

This is what I was going to do... (probably way wrong!)

1. adjust main idle screw to full open position
2. using a small drill bit adjust all butterfly valves to open and close to the same point
3. using the same drill bit, adjust the slides so that they all have the same gap just before them reach the bottom
4. adjust main idle screw to "stock setting"
5. done!

Please correct me if I'm sounding like a pillock!

Thanks for your help in advance!

Fraser

flybox1 · « **Reply #1 on:** July 08, 2016, 10:00:52 AM »

I would add, between steps #2 & #3, turn all your vacuum sync screws to the same threads showing...like 4-5 threads, and lock them back them in place with their lock-nuts. If they're all pretty close, then no need.
This just prevents you from running out of adjustment room when vacuum syncing.

Fraserimoore · « **Reply #2 on:** July 08, 2016, 12:29:45 PM »

Thanks for the reply Guys, However...I'm struggling

What I've done so far:

1. Backed off idle screw/knob so that slides go towards the bottom
2. chose #1 as master and locked the nut to prevent movement
3. began adjusting other carbs to match #1 (attempting to get them all to reach the bottom)

The PROBLEM:

The gap on #3 is still slighty great than the other 3.

Once I identified the master - adjusted it and locked it, should I have turned the Idle screw back in to raise it up? and only then start adjusting the other 3 carbs using the drill bit method. Becuase if Im tryin to get them all to reach the bottom the drill bit wont fit.

I hope this makes sense.

harisuluv · « **Reply #3 on:** July 08, 2016, 12:35:06 PM »

Really the fool proof way (almost) to do this is: We'll use a 1/8" drill bit for the example tool from airbox side. Get all the slides off "the deck" that way nothing will bind and throw everything else off. Designate #2 the master. Back off the idle screw so it's not making contact. Now get the nut on #2 to where it has about the normal amount of threads showing like you want on your picture on the right (3-4 threads, 4 is good). Now here's where the foolproof part comes in: You have only set where you know the threads at the top are a perfectly acceptable honda factory level which allow for range of adjustment via the idle screw. None of the other slides are BELOW the level of #2 (which would mess this up). Now, adjust #2 with the IDLE SET SCREW with your drill bit (just close). Verify range of motion IN and OUT with the idle adjust screw (should be making contact with the stop when turning in and out for providing a reasonable range of adjustment). Next, fine adjust #2 with your drill bit (or whatever). Now you are going to have for sure the sync set IN RELATION to the idle screw. In other words, you're not going to get them all synced to each other only to find when you adjust the idle screw it's not even touching and you have no adjustment! Now all you have to do is set the rest to the same level as #2 (adjust each with the individual adjuster, you don't need to really mess with the main idle adjust now). Easy!

Fraserimoore · « **Reply #4 on:** July 08, 2016, 01:06:55 PM »

Thanks for the help.

I think i'm missing something as if I were to leave 4 threads on the adjuster screw and idle screw backed off i still wouldnt be able to get a 1/8 drill bit in the gap...

What ive ended up doing is:

-backing off the main idle screw
-chose any carb as the master and moved the slide as close to the bottom as possible (no gauge/tool used) - locked it
-adjusted the other 3 to get as close as possible

I've added some pics which hopefully you can see the gaps with the main idle screw backed off completely with no contact...

harisuluv · « **Reply #5 on:** July 09, 2016, 11:54:52 AM »

Wrong side. You use the drill bit on the other side (air intake).

Scott S · « **Reply #6 on:** July 09, 2016, 01:42:04 PM »

I've never used it on the intake side. The butterfly's are in the way and the cutaway is on that side. I always do it on the engine side.
Maybe I'm doing it wrong, but it works.

Scott S · « **Reply #7 on:** July 09, 2016, 04:17:37 PM »

I was referring to this, where he says "air intake" side. To me, that's the air box side and I don't see how you do it from that side.

Quote from: harisuluv on July 09, 2016, 11:54:52 AM

Wrong side. You use the drill bit on the other side (air intake).

harisuluv · « **Reply #8 on:** July 09, 2016, 04:20:04 PM »

Quote from: Scott S on July 09, 2016, 01:42:04 PM

I've never used it on the intake side. The butterfly's are in the way and the cutaway is on that side. I always do it on the engine side.
Maybe I'm doing it wrong, but it works.

It can work, however you run the risk of potentially running out of range of adjustment with the idle screw that way. If you bench synced them from the engine side the first start would greet you with an insane idle speed. The choke flaps are no obstruction at all for bench syncing.

Scott S · « **Reply #9 on:** July 09, 2016, 05:43:28 PM »

I mark the idle screw then raise the slides enough to use my "dealer gauge". I count how many turns it takes to raise them, using the mark I made, and then lower them back. Works for me with very minimal adjustments needed once on the bike.

Deltarider · « **Reply #10 on:** July 10, 2016, 07:51:21 AM »

Quote

I've never used it on the intake side. The butterfly's are in the way and the cutaway is on that side. I always do it on the engine side.
Maybe I'm doing it wrong, but it works.

That's my method too, only I use a small allen key. I fail to understand what's so magical about a drill bit. Maybe it is one of these echoes in the forum.

754 · « **Reply #11 on:** July 10, 2016, 09:59:50 AM »

Allen key can be. Scratchy..
I use polished rod..brass and roll it sideways.. You can get within a few thou. If you dont roll it and check it a few times it will fit different. One of those time.
So roll it, and get even closer..

jakec · « **Reply #12 on:** June 19, 2019, 09:45:04 AM »

I bench sync'd by 550 carbs, and I used a small drill bit (smallest I have, about 1/16" maybe). I looked from the engine side. Now I finally started the bike and it idles 2-3k rpm, idle adjustment screw fully backed out. Have I made a mistake?

Medyo Bastos · « **Reply #13 on:** June 19, 2019, 10:30:09 AM »

Use your drill bit on the other side

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jakec · « **Reply #14 on:** June 19, 2019, 10:31:53 AM »

Quote from: harisuluv on July 09, 2016, 04:20:04 PM

It can work, however you run the risk of potentially running out of range of adjustment with the idle screw that way. If you bench synced them from the engine side the first start would greet you with an insane idle speed. The choke flaps are no obstruction at all for bench syncing.

So I need to sync off of the air intake side, where the reliefs are? Damn..

Medyo Bastos · « **Reply #15 on:** June 19, 2019, 10:35:49 AM »

Correct, and adjust your idle to give you a slight drag on #1 carb; adjust the other 3 to match number 1; pull drool bot out, and adjust idle down before start engine

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jakec · « **Reply #16 on:** June 19, 2019, 10:42:23 AM »

I just asked my friend about it and he said he has a vacuum sync tool, so I shouldn't bother takin them back off and we can just adjust them down on the bike. That should be fine right?

TwoTired · « **Reply #17 on:** June 19, 2019, 10:50:25 AM »

The early 500/550 carb don't have a designated master carb (#2) like later ones do. If you chase all the slide adjustments, you can end up with slides that can't fully close.

So, pick a carb to be the master and with the idle knob backed out ensure that slide can fully close. Lock that one down and never adjust it again. It is now your designated master. Adjust the others to it's opening or vacuum level from now on. Then use the idle knob to set minimum idle and all carbs will obey.

Cheers,

jakec · « **Reply #18 on:** June 19, 2019, 11:45:02 AM »

Thank you! will do.

cjespersen · « **Reply #19 on:** June 19, 2019, 08:55:22 PM »

Also when your finished make sure the slides drop all the way down when the large idle screw is turned all the way out. If not your bike will idle high and race out of control because it's getting to much air.

jakec · « **Reply #20 on:** July 23, 2019, 04:06:13 PM »

My friend with the vacuum gauge just had a kid and he's busy now, so I guess I'm just going to take the carbs off and bench them again.

So should I fully close #1, lock the screw/nut, then lift the #1 slide with the idle screw until the drill bit I'm using fits? Then adjust 2, 3, & 4 to the drill bit with the idle screw in. That way I have the option of full range of action on the idle adjustment?

Bodi · « **Reply #21 on:** July 24, 2019, 05:44:10 AM »

You need to avoid having the idle screw unable to adjust the idle, that happens when you start messing with all four adjustments.
- loosen idle screw all the way
- pick a master carb (does not matter which one, but 2 & 3 are harder to adjust when running because of the frame so usually we pick one of them). Adjust it so the slide just fully bottoms and then maybe 1/4 turn further.
- Lift that slide with the idle screw to fit your bench sync rod in the slide gap.
- I lock this adjuster with nail polish, but maybe you don't use it. A bit of paint will do.
- Do not touch the idle screw again. Use the adjusters to set the other three slides to your gauge rod.
- Done. The idle RPM you get is unpredictable, depends on what size rod you used. But it will be adjustable with the idle screw.
- proceed to do a vacuum sync - after the valve lash and ignition timing is set up. You should set all the pilot screws to factory spec then make small adjustments (1/8 turn is good) equally to all four to get the best idle and minimal stallout on throttle opening. For the vacuum sync, DO NOT adjust that master carb: adjust the others to get matching readings.

jakec · « **Reply #22 on:** July 24, 2019, 08:59:43 AM »

Awesome, thanks. I have already done the rest of a the full tune up ( already rode the bike 120 miles). Just had an idle of 3,500 rpm the whole time.

jakec · « **Reply #23 on:** July 25, 2019, 08:52:59 AM »

Did the procedure as described above and it worked great. Bike is idling nice and low now with plenty of room for adjustment.

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Author Topic: CB550 Bench Sync Procedure help (Read 8154 times)