Topic: 74 CB550 - Carb Sync'ing Problems!

[StormeeBee]

Hey Guys,

I've run into an issue while sync'ing the carbs on my 74 CB550. I've got the tool (Motion Pro Carb Sync Tool) and set it up/calibrated it just like you're supposed to. Since there's no Master Carb on these bikes, we took Carb 1 as the Master. We set it to an appropriate level and calibrated on of that.

We started sync'ing and our biggest issue is that adjusting one carb sends 1 or two other carbs spiking through the roof and I can't tell if there's any rhyme or reason why certain carbs are spiking and some aren't. Is there an order that I should be sync'ing in? Does anyone have any tips to make this process easier?

[Duanob]

You kind of answered your own question. There is no master carb so you can't really 'set' one. I've always gone back and forth until everything is running at same level. Adjusting one will throw another off a bit so it's trial and error but you will get it eventually. Also you will notice the idle jumping around when you adjust each carb. Just keep the idle as low as you can until all carbs are synced then set the idle at ~1200. Don't forget to blip the throttle every once in a while after making adjustments.

[harisuluv]

Each carb has to be adjusted in relation to the idle set screw on the linkage which controls all the carbs.

Carbs 1and2, 3and4 are connected with little shim like strips which you probably know of.  They are thin and work as a stabilizer for each pair, but if your adjustments are out of a certain range, they will pull or tug on the other "neighbor" carb and can alter it.  Some change between pairs while you're syncing is normal, you gotta just fiddle with it.

Now, as far as adjusting one carb and other carbs in the other pair being affected, well that's probably an issue with you adjusting til one slide hits the bottom and, of course, it physically raises the entire linkage.  Which goes back to the first sentence.  This is where a good bench sync helps to get a lot of these values dialed in really close so you don't have to worry about staying within the range of adjustment.

Syncing without keeping in mind the idle adjust screw can also mean that it might have no affect cause where each carb is set the idle adjust screw might not even be touching.

As a guideline, here's an easy trick.  If the individual carb adjust screws have 3-4 threads showing above the nut, you will be able to sync with enough range of motion in the idle adjust screw (probalby). 

Knowing that, first get all the slides off the deck, so you aren't hitting the bottom.  Select one carb as master, get it to that 3-4 threads showing, and then set idle adjust to whatever size drill bit you have (around 1/8").