Topic: Carb Sync instructions

[jcslocum]

I'm tuning my '74 550 and for the life of me can't find a real good instructions (with pics if possible) of the complete process. I have done some searches on the site and haven't found it yet. Can someone point me in the right diection??

[1timduke]

Are you attempting a bench sync, or a vacuum (well worth it) sync?

-Tim

[Johnie]

What kind of info are you looking for?  Keep in mind the sync is the last thing you do once the valves are adjusted, points, plugs and timing are done.  And the carbs should be clean.  If you are at that spot, then you will need a reliable sync gauge.  I use the Morgan Carbtune which many guys here like. 
Warm the engine up maybe on a ride.  Find your vacuum screws and remove them.  Connect the gauges, put a large fan or 2 on the front of the motor so you do not over heat it.  Start it up and see how close you are on the gauges.  I do not know if your bike has a slave carb or not.  That is a carb you can not adjust the sync, but instead the other 3 carbs are adjusted to that one.  Other guys on the board with the 550 can chime in on that issue.  So once you determine where you are at you can adjust the slides so all are about equal vacuum.  I hope I provided you a little insight into the steps.  Ask questions if you need more info.  Good luck with it.  A good sync can make for a great running bike.

[Sporkfly]

Unfortunately I don't know what to tell you for the earlier carbs. For what it's worth, on the '77 carbs you pull the top covers and there is a locknut and a screw you'll see. This adjusts your slide opening. With the engine warm and a fan on it, hook up your gauges and fire it up. Adjust those screws until you have equal vacuum across the rack. It's actually a pretty straight forward process and I was pleasantly surprised at how easy it was when I was done.

And yes, a vacuum sync is WELL worth it. My bike pulled much smoother afterwards, the clutch action felt better, the throttle response was much snappier, idled lower... Good luck and hopefully somebody else can help you out with the earlier carbs.

[the technological J]

i just sychd mine its really simple dont worry just find out the deal for ur carbs and ur set.... what kinda carbs u got? they should have some letters on one of the sides(not MADE IN JAPAN)

[r6100mph]

Sound very intimidating at first, but after the first one, it's a 15 minute process. 

Good question regarding what type of sychronizer you're using. 

I have a morgan carbtune, vacuum guages, and it's so simple to use. 

Never tried the mercury guages, so I can't tell you how to use them

But Johnnie basically summed it up.

[jcslocum]

I want to do  running sync.

I have a Motion Pro Carb Mercury Carb Stick.

I have done lots of twins so I'm very familiar with the process, just never worked om 4 carbs at once. I though there was 1 carb that was not adjustable and that the other 3 carbs had to be set to match that one. My carbs have 4 adjusting screws with lock nuts so I assume all 4 can be adjusted.

All other adjustments have been made. This is the last one to do.

[Cvillechopper]

What carbs do you have?  The numbers/letters will be stamped on the side.  For the earlier carbs (I've got the 627B set) you can adjust all 4.  Some have one cylinder that is not adjustable and you adjust the rest to match that one.

[KCRSXTypeS]

I don't know why everyone here is saying its so easy...I think its a pain in the ass...pull the tank, pull the seat.  Then start adjusting each carb as it is running but when you change one to increase the vacuum the other three lose vacuum but not equally and when you are trying to do it you have to adjust the idle screw position as well.  As you are doing all of this you are trying to get your vacuum to be set at ~7 in. of mercury but can't get it there...PAIN IN THE ASS!

[Duke McDukiedook]

Time consuming, yes, pain in the ass- well that is for each person to decide.
Set your reference carb (in my case 8-10psi in #1) and then get equal readings in all the carbs, that is good enough unless you are racing.

This is usually something only done in a blue moon when you make major changes to the intake system or the PO left you with gremlins.
This isn't something you do every other week.

[Johnie]

One other point...keep in mind as you adjust a carb it will usually change the other ones a bit.  So you will have to go back and forth to find that "happy spot." 

[KCRSXTypeS]

One other point...keep in mind as you adjust a carb it will usually change the other ones a bit.  So you will have to go back and forth to find that "happy spot." 

Yea, I had to keep going back and forth and back and forth...finally, the idle screw was screwed in so far that it couldn't adjust anymore...thats when everything went crazy...

[Gordon]

I don't know why everyone here is saying its so easy...I think its a pain in the ass...  As you are doing all of this you are trying to get your vacuum to be set at ~7 in. of mercury but can't get it there...PAIN IN THE ASS!

You're making it harder for yourself than it needs to be.  You don't need to aim for a specific level of mercury.  All you should be concerned with when synching the carbs is that they're all at the same level.  In fact, one thing I've recommended to a few people who kept getting distracted by the numbers on the synch gauge is to put a strip of tape over them so you can't even see the numbers anymore. 

[bistromath]

One little hint: you don't have to pull the tank. Unhook the rear tank mount and prop up the rear of the tank with something. This will let you get in there and adjust the screws without having to rig the tank up with long fuel hoses. Also, adjust all 4 for mercury first. Then adjust the idle mixture screws. Get a good digital tach if you really want to get the idle screws set right, and adjust for maximum RPM at idle. Do each carb a quarter turn or so at a time, and snap the throttle in between adjustments. It's a real pain in the ass and it's probably totally unnecessary but when you're done man it sure idles smooth as silk.