Better info needed on how to sync.

[Yard Dogg]

I've been all over this forum reading the threads about syncing carbs and still haven't found an answer to my question, no offense to any of you intended. I understand they all need to have the same vacuum reading, but is there a specific vacuum volume that I'm looking for? 10 pounds pressure for each 1? 20 lbs pressure for each one? Does it even matter. On a car when you use a vacuum gauge to set your fuel air mixture, you hook up the vacuum gauge and turn the screw out until the most vacuum is achieved. Do I need to do that on my bike? Would I adjust one pilot screw out until I get the highest vacuum reading and then balance between all four to have the same reading? I know the pilot screw has to do with the fuel air right? So if I just set them all where they are pulling the same vacuum, how do I know if I'm getting the right fuel air mixture on any of them?

[MrOzz]

Actual vacuum reading is not important.You just need all four carbs to have the same reading.

[Rettic]

Sync

Well, first off, with the sync, all you are looking for is that all are the same. Then you adjust the idle to 1100 rpm. I usually set the idle to 1200 to sync. I then just 1-2 to the same level, then 3-4, and then 2-3. Keep the idle around 1200. It will fluctuate while adjusting.

As for the mixture, I am a huge fan of the colortune. You sync the carbs, then put the colortune in the first one and adjust to a Bunsen burner blue. I think the directions are take adjustment to yellow then to where you barely get a color, then half way between. I am not good at tuning by ear like alot of old timers are. Hope that helps and I welcome anyone to correct me where wrong.

[DGXSER]

Here is a pretty good video of the process.

Carb Synching

[Larrym]

Gauge This??

Here's a Krappy video of what I saw after doing the sync on my 79 Special:



here's a pic of the gauges with no vacuum/at rest:




My reading? Maybe 5-6 psi at idle. ( Or is it inches of vacuum??) I guess your readings wouldn't be much different. The video is just after doing the "carb 3 matched to carb 4, carb 1 matched to carb 2, and the carbs 1+2 matched to carbs 3+4 " procedure. Just a matter of finding the right screws in between the correct carbs and turning the screws while looking at the gauges. Sounds really complicated but this is one of those things that we learn by doing. Not talking about, but doing. Afterwards all mysteries are gone.

That tuning of the individual carb idle air/fuel mixture can be done by ear or by using the fabled "Colortune". By ear it's much the same as when you do it on a car. In particular an accurate external tachometer is needed. The tach on the bike isn't accurate enough to do the "ear" method IMO.

[XS1100 Newbie]

It almost sounds like he was trying to synch by adjusting the air/fuel mixture screws, instead of the proper screws between the carbs. I adjusted the air/ fuel by ear, and then synched.

[Yard Dogg]

My intake butterfly valves will be synced first. When I sync the pilot screws I don't just want to make em the same, I want to get the right air fuel mixture as well. The color tube sounds like a good idea for that part. I think I've got a pretty good idea of it now. Thanks all.

[Yard Dogg]

Okay I'm confused. I thought I was supposed to sync the throttle flaps with feeler wire before I put them on and then sync the fuel air mixture with the vacuum gauge.

Now I'm thinking this, tell me if I'm right.
#1 Set the throttle valves with feeler wire.
#2 Put carbs on.
#3 Set mixture screws with color tune.
#4 Sync throttle valves with vacuum gauge or mercury.
#5 Recheck mixture with color tube.

How am I doing now?
Funny, all this time I've been sitting here thinking, how the hell can that little pin hole for the fuel air screw effect the vacuum enough to get an accurate adjustment. I even have a book, what a brain fart.

[Larrym]

The Hills are Alive with the Sound of Tuning

Okay I'm confused. I thought I was supposed to sync the throttle flaps with feeler wire before I put them on and then sync the fuel air mixture with the vacuum gauge.

Now I'm thinking this, tell me if I'm right.
#1 Set the throttle valves with feeler wire.
#2 Put carbs on.
#3 Set mixture screws with color tune.
#4 Sync throttle valves with vacuum gauge or mercury.
#5 Recheck mixture with color tube.

How am I doing now?
Funny, all this time I've been sitting here thinking, how the hell can that little pin hole for the fuel air screw effect the vacuum enough to get an accurate adjustment. I even have a book, what a brain fart.

No. You're on the right track: thinking things through before tweaking things. (Going "Cowboy" on these bikes can sometimes have less than happy results: Just do a cam chain tensioner adjustment search and you'll find folks that wish they had looked before they leaped....)

Setting the throttle butterflies with the wire is part of the bench sync process which gives you a fighting chance to get the bike started/close to where you'll end up as far as the butterflies are concerned. That's a good #1 choice.

#2. Putting the carbs on: I see that as a necessary and properly ordered step.

#3 Setting the idle mixture screws at this point with the colortune?? My vote is no. Others may chime in here but I'd say at this point it's ok to just lightly seat the idle mix screws and then to back them out 1 and 1/2 turns. (Many a screw has had the tip broken off by a ham-handed approach to doing this so go easy.)That's usually a good enough starting point to get the bike running. The final adjustment is made with the colortune or by ear but only after the carb butterflies are adjusted (synchronized with the others) via the screws in between the carbs. The idle mixture screws are only a minor adjustment and not the "sync" screws.

#4 Sync'ing the carbs with the sticks. Yep. Have at it. Use the screws in between the carbs to adjust the butterflies which end up setting the major vacuum readings of each carb. The oddball sequence of sync'ing owes its order to the fact that #3 carb is the one that all other carbs must be synced to.

#5 Colortune or by ear it's time to set the idle mixture for each carb. There will be minor changes in the idle speed as a better mixture on each carb is done. This means that the overall idle speed must be turned down by way of the big knurled adjuster located in the very center of the carbs between #2 and #3. The "by Ear" method is detailed in the following thread:

http://www.xs11.com/xs11-info/tech-t...colortune.html

#6 Hah! Didn't think there was a #6, eh? Well after adjusting the idle air mixtures on all 4 carbs then it's time to go back and re-verify the sync again. Remember that the sync adjusting screws are the ones located in between the carbs next to the butterflies: not the idle air mixture screws located in between the carb boot and the carb body at the top of the arced circle.

I remember the first time I had to do this: it was exciting and a little scary. Maybe it's just me but every time I do it I feel the same way.

Never grows old or dull.

[Erik the Red]

Step 2.5

#2. Putting the carbs on: I see that as a necessary and properly ordered step.

#3 Setting the idle mixture screws at this point with the colortune?? My vote is no. Others may chime in here but I'd say at this point it's ok to just lightly seat the idle mix screws and then to back them out 1 and 1/2 turns. (Many a screw has had the tip broken off by a ham-handed approach to doing this so go easy.)That's usually a good enough starting point to get the bike running.

Important! Get a fan (the box or oscillating kind -not the neighborhood kid who holds you in high regard) and point it at the running stationary engine!!

You do NOT want to just keep the engine running (for as long as this will take) without airflow over the cooling fins, to, well, cool the engine. Bad things can happen when the engine overheats.

[mack]

colour tone

I"m unfamiliar with this unit. From what I've read though and as I understand it. The colour tone tuning of the idle mixture compensates for the atmospheric pressure at different altitudes?

[81xsproject]

Lots of good info. My 2 cents on syncing carbs; a very good bench synch will make the dynamic synch MUCH easier. Hell, a GOOD bench synch will have the thing running so smooth it will make you consider not even bothering with a dynamic sync. Set the idle mixture screws to uniform number of turns out before starting (confirm that the tips are in good shape first).

As for synch tools, you just cannot beat the homemade, four-way linked, vinyl tubing manometer (and you REALLY can't beat the price).

[CatatonicBug]

Okay I'm confused. I thought I was supposed to sync the throttle flaps with feeler wire before I put them on and then sync the fuel air mixture with the vacuum gauge.

Now I'm thinking this, tell me if I'm right.
#1 Set the throttle valves with feeler wire.
#2 Put carbs on.
#3 Set mixture screws with color tune.
#4 Sync throttle valves with vacuum gauge or mercury.
#5 Recheck mixture with color tube.

How am I doing now?

I would say you have it almost right.
You can probably skip #1 unless you tore the whole carb bank apart, as long as you are going to do the rest immediately.

Then:
#2
#4
#3
#4

Sync before and after the colortune, though you probably won't have to do much adjustment at all for the second sync. Also, as Erik says, use a fan to keep the temps under control.

[TomRodgers]

Depending on how far off the mix screws are or how far off the sync is, you may have to RADICALLY change the idle screw mid way.....When doing 'Sunshines sync, i didnt really know what 'bench sync' meant...even after reading the posts....sooooo i did it anyway...my bench sync must be WAY different that the guru's, cuz it was "on" enuf to run, but "off" enuf to run like crap...but that coulda been cuz of the mix screws being WAY off... I got her started, set idle to around 1200 rpms.....shut her down, put color tune on #1. Plug showed evidence of being LEAN. backed screw out while running until blue color was present...idle went up to almost 1800 rms....had to back it down...Same story with #2. #3 was RICH..backed it down,and idle dropped a bit...#4 was lean also....idle went up. I set it back down... Hooked the guages to the carbs, and was relatively close. i dialed in the sync....then checked with colortune again...everything seemed okey dokey. Throttle response was smooth and exact. cant wait to get the brakes fixed to try it out!!!

[DGXSER]

Alot of this has to do with the condition of the engine. On Thunderstruck, a bench sync and 2 turns out was almost ideal all the way across. Barely any change needed, but then my compression is almost identical all the way across on that bike, right at 150 psi.

On Banshee, the project bike, compression is all over the board. So each cylinder draws a different level of vacuum for the same amount of fuel at the same mixture.

On Banshee, when I first fired it up, she ran fine on choke. As she warmed up and came off choke, every time I gave it throttle it stayed there for a while. I had to drop the idle down from 4k to 1500 by the time it was warmed up. Until I synched the carbs up, now it needed more idle. And boy were they ever off. Anything from 5" up to 12". Now they are very close on the synch at about 8" and I need to colortune, then synch again, then recheck the colortune......wash, rinse, and repeat until all looks good. If the compression on the bike comes back as is anticipated, then the process will start all over again.

Tuning, mixture setting and synching, is a "system" performance issue, not a carb performance issue. I could pull the carbs off Thunderstruck that are definitely tuned well for that engine, put them on Banshee and they will be off by a few hockey rinks.