Topic: Carb Sync Screws

[gregripko]

If I backed the adjustment screws out a descent amount but was still able to balance carbs (vacuum sync), will this effect bike? Is a solution to just turn all 4 carb adjust screws an equal rotation to the right to still maintain sync? Seems like the idle adjust screw on the bottom right side is less effective now after sync.... Also what's an effective way to tighten the outside nuts to the carb screws after syncing? It's difficult to fit a wrench in there while holding screw position in place.

[Rigid]

Type of bike?

[flybox1]

has your vac gauge been calibrated?
did you do a proper bench sync?
strange that all screws could be turned the same in one direction and you still have sync. 

your idle adjust screw is used during a sync to help maintain a good idle during sync and it will change depending on your small vacuum changes.  it should adjust your idle easily way up and way down.

box wrench on the nut with a standard screw driver in the adjustment screw, or the slick Motion Pro combo tool 

...and when you do properly tighten the locknuts, they will make minute changes to that carbs vacuum unless you're paying attention to the adjustment screw.

[bjbuchanan]

As long as you are not at like extreme ends of adjustment i.e. all the way down or up where you can't rly adjust anymore you are fine. Your idle adjustment knob is ineffective because you did your sync wrong. What you want to do is to basically back the idle knob off so it does nothing then just get the bike to run with the screws how they are. That's what that drill bit thing is useful for because your bike will atleast now run

After you get it to run you use the idle adjustment knob to get it up to say like 2k~ and adjust. Try to work the idle down nice and low and get it synced there. Starting at 2k makes it easier for way out of whack carbs

To tighten the screw you can use one of the special tools that is like a long reach weird wrench. I just used a cheap 10mm because it is thinner and a cheap bigger wrench to hold it so no interference. I have a feel for it because I have adjusted valves too so you get a technique to not really disturb it

Also you can't just turn the four screws because that was the purpose of syncing. The carbs are not mechanically identical, cylinders flow different because of wear and carbon buildup, minute differences are what you are correcting. That is why it runs, just not super smooth. Your functional but not perfect. The same turn for the four diff screws will yield varying effects which will then change sync.

Get it? good, go do it

I'm sure plenty of ppl will chime in too, good luck with it. Once you figure it out you will be moving fast

[gregripko]

Can you explain what you mean by this:

"back the idle knob off so it does nothing then just get the bike to run with the screws how they are"


Also...should the air mixture screws be reset a certain way before sync? or adjust mixture screws after sync?
It has been said that the screws should be turned out 1.5 turns from seated....does that mean each air screws rotates 540 degrees out from the seated position (all the way screwed in)?

CB550K 76'

[bjbuchanan]

The idea behind backing the idle knob off is that you get the bike to run without a crutch, like having to hold it open with your hand. If you bench sync with a bit to 1/8 it will run

What I mean by backing it off is so that you don't have once carb so out of whack it is closed normally and the only reason it is running is because 3 of them are wide open and the one is cracked. Just try to have all your slides roughly equal and use the knob to fix it at a low rpm like 2 grand

Set the mixture at your stock amount of turns. Don't mess with any of that stuff while you are trying to sync it will just mess you up and is not part of a sync. That is fine tuning stuff.

Yes, 540 degrees from gently seated. Don't confuse a half turn with a whole, vice versa

[gregripko]

gotcha........ok so i backed the mixture screws out to 2....manual says (1.5-2.0)...seems to be running decent...

when I synced it originally i turned the idle screw down to 1500-2000 rpm....but maybe i'll resync again because i know I'll have to tighten up those outside bolts a little better....just couldnt get to them very well with a small 10mm :/ wrench

[gregripko]

btw...on a side note....

I notice the part that the carb sync screw goes into (the screw that you adjust when syncing carb)....is very loose....sorta like a loose tooth.... not the screw that you adjust for carb sync...but the piece that the screw goes into...it wiggles....is that normal?

[TwoTired]

gotcha........ok so i backed the mixture screws out to 2....manual says (1.5-2.0)...seems to be running decent...

when I synced it originally i turned the idle screw down to 1500-2000 rpm....but maybe i'll resync again because i know I'll have to tighten up those outside bolts a little better....just couldnt get to them very well with a small 10mm :/ wrench

You want to vacuum sync at the lowest RPM closest to idle spec (1000).  If out of sync it won't idle well there.  So, it becomes a reiterative process, until things are better balanced.

Opening the air bleed screws more than spec. will just make the throttle twist response poorer. The setting won't matter much with engine stationary/no load. (Unless your air filter is clogged up/dirty.)  If the air filter is clogged/dirty, you have no business syncing anyway.  In fact, the entire tune up check list should be done done before vacuum sync, or you will almost certainly need to do it again after the next tune up cycle.  Tappet clearances off, can/will change the vacuum sync, for example.

Syncing the earlier 550 carbs is way easier with the proper tools.  I made the one below.

[gregripko]

i'll take the idle screws back to 1.5....and resync... awesome tool btw! did you heat that wrench with a blowtorch and just bend it?

[TwoTired]

atcetylene

[dave500]

socket welded to small spanner,screw driver fits through it.

[gregripko]

Do you guys know the MM size for the carb nuts?

[goldarrow]

8mm

[gregripko]

Ty