Sync carbs

[XS1100_OEM4ME]

Was ask a question from a fellow member, he was told by a bike mech "if your bike idles OK, you don't need to sync your carbs, as once you open the throtle, sync doesn't matter" Is the mech right, why sync (I sync mine, just looking for input for him

[DGXSER]

In my opinion, No, the machanic is looking at a small part of the picture. My bike has sounded fine at idle, and then I colortuned, and synched it and I wondered why I waited so long to do it. The overall performance was much improved.

I believe you have to look att he root of the need to synchronize, it is not to achieve a consistant idle, it is to match the power production of each cylinder to one another. So your bike might idle evne enough, but might really be off on the mixture or the amount being delivered to each cylinder for power production. So then it becomes more pronounced as the power is increased, the difference that is. So you can have one cylinder doing much more work than the others. Granted, if they were THAT different it shoudl show up in the idle. But again, I have noticed the difference wehn I thought all was well to start with.

At the end of the day, it is a judgement call. Its like shimming valves, the bike will run with them out of spec, and you can tune the idle even with mixture screw adjustments to counteract the valve issues. But you still have valve issues. If you have done it a few times, a synch is not that tough to do. Takes longer to change the oil really. So the question for me is not why would need to synch, but why would you not want to synch.

[XS1100_OEM4ME]

Well put

+1 and well put, like I said, I sync mine, easy to do and one more thing not to worry about

[DAVINCI]

that "mechanic" is an idiot.

[Laptop_geek]

that "mechanic" is an idiot.

+1, Always sync your carbs, if not a full sync, then at least bench sync. There has never been a bike that has had lower performance after syncing the carbs. It would make since to me that an engine with carbs that are in sync would place fewer stresses on the components than one that is out of sync. If that were true it would mean that by syncing your carbs your engine could actually last longer (I'm not claiming this to be true, just a thought). If that were true it would be a very minute point, but a point none the less.

[DGXSER]

Just because this seems to be a popular misnomer, bench synching the carbs is merely a way to get them close enough the bike should run decent enough for you to be bale to acutally synch and tune the mixture of the carbs. It is not synchronizing the carbs, it is simply making sure all four butterfly valves are open the same mount. As outlined earlier, synching is how you adjust each cylinder to be equal when the valve lash, ring seals, and minor differences in exhaust pipe lengths all lend to each cylinder being just a little different.

Sorry if this comes across as a rant, it is not intended to be or to be jumping on Laptop-Geek. Over the years I have seen several misguided folks who thought that a bench synch is all that is ever needed, that it is the same as synching the carbs in operation. It is not and I just did not want someone coming away with the wrong idea about it.

That said, when I clean a set of carbs I do bench synch them, it is a good practice, just not a substitute for an operating synch.

[XS1100_OEM4ME]

Well put

Well put, and that is why carbs sync is important, unlike a car motor that all cyls feed from one intake manifold, the XS1100 is like 4 motors linked togather all feeding from their own intake manifold and carb If not synced, you don't have even pull between those 4 motors, not just at idle, but all through the rpm curve

Just because this seems to be a popular misnomer, bench synching the carbs is merely a way to get them close enough the bike should run decent enough for you to be bale to acutally synch and tune the mixture of the carbs. It is not synchronizing the carbs, it is simply making sure all four butterfly valves are open the same mount. As outlined earlier, synching is how you adjust each cylinder to be equal when the valve lash, ring seals, and minor differences in exhaust pipe lengths all lend to each cylinder being just a little different.

Sorry if this comes across as a rant, it is not intended to be or to be jumping on Laptop-Geek. Over the years I have seen several misguided folks who thought that a bench synch is all that is ever needed, that it is the same as synching the carbs in operation. It is not and I just did not want someone coming away with the wrong idea about it.

That said, when I clean a set of carbs I do bench synch them, it is a good practice, just not a substitute for an operating synch.

[latexeses]

"sync doesn't matter"

If you only have one carb.....

[bikerphil]

Most mechanics will say "close enough" if it runs ok their job is done, they don't have to ride it every day. Sync your carbs for optimal performance. Although I ran mine for 10yrs without syncing and they were cleaned/removed several times, the bike ran acceptable.

[TADracer]

Sync'ed carbs are not important if you run at WOT. As long as you are in the midrange or on the pilot circuit (where you are most of the time) sync'ing the carbs is invaluable. You are not adjusting the amount of fuel the carbs are giving, you are adjusting the vacuum pull on the carbs to even things out.

If you ever wonder if you are out of sync, cruise at about 50 mph and listen closely. If your motor seems to wonder up and down a bit then I bet you are well out of sync. Same reason that a pilot sync's his motors on a multi engined plane.