XS1100H Carb Sync Issue

[MPittma100]

I have easily synced carbs on a 79 Special, but am having a problem with an 81 Venturer. I can get 1 & 2 together. I can also get 3 & 4 together. But I am not able to bring the two pair together on the carb tune. The left two columns are considerably higher than the right two. If I adjust number three screw to match the 4 colums, the idle goes way up and the rpm will slowly return to idle.

I notice thay I can back the main idle screw away from the tab and it will still idle. If I leave the left colums higher, it appears to idle, rpm, and return to idle properly. So what am I missing?

MP

[DGXSER]

Since you say the idle screw will nto bring the idle down low (should bring it down enough to kill the engine). I wonder if your throttle cable is hung up on something. Does it have slack at the grip?

[MPittma100]

Cable

I looked at that. Even put all the slack in the cable with the adjuster. Idle screw will bring idle down to slower idle.

MP

[DGXSER]

Hmm...are your mixture screws adjusted? Have you checked the restrictors in your lines on the carbtune to be sure one or two are not partly clogged? Reaching a little perhaps but JAT.

[jetmechmarty]

Mike,

You need to pull the carburetors and bench sync them again. You're syncing everything to #2, correct? I think it's open too far to begin with and you're opening everything else to match. At least, that's how my brain wraps around the problem.

I had the same or similar issue and brought it here. I took the carbs off and bench synced them again. All is well.

[CatatonicBug]

Mike,

You need to pull the carburetors and bench sync them again.

If the bike is running at all, there is no reason to bench sync. That process is only to get it "close enough" to start the engine. He's already gotten that far.

Not sure what you mean by the difference between "idle, rpm and return to idle". All of the sync process is done at or below a normal idle speed (i.e., 800rpm). Never give the bike gas while you sync the carbs. If the 2 pairs of columns on the carbtune are even, then all you need to do is bring one down and the other up with the sync screw between the 2&3 carbs. Fine-tune a little after that, and you're done. It is normal for the idle speed to rise when you get closer to being sync'd, because the engine will be running more smoothly. Simply turn the idle screw to drop the idle speed back down to 800 or so. Once it's all done, turn the idle back up to 1100 rpm, and you're all set.

[natemoen]

Marty, it is #3 that you sync to. The third carb from the left while sitting on the bike.

[bikerphil]

I've run into that issue before, carbs being so far out of whack that I needed to bench sync them first, the bike ran kinda ok but I couldn't get the gauges anywhere close, +1 Marty.

MP, check your sync hoses for cracked ends, or you may have leaks at the carb boot/head, JAT

[MPittma100]

Sync Issue XS1100H

What I meant about return to idle:

After having synced 1&2 and 3&4, the next step is to bring both pair of columns equal with carb screw between 2&3 carb. Prior to touching that screw the carbtune shows columns 1&2 considerably higher than 3&4. The engine is idling good, the throttle response is good, and return to idle from a snap of the throttle is quick (normal).

When I start turning the screw between 2&3 to bring all columns equal, the idle starts going up quite a bit. At this point, if you rev the engine up, it will very slowly (too slow) return to idle.

So, I can get the columns together with the screw, but it is not running correctly when they are. If I back the screw (between 2&3) back out where the columns are unequal (2 left higher than 2 right), it runs best. Only thing that I notice, is some light popping in the exhaust on decel on a test ride.

These readings on the carbtune is where they were when I hooked it up initially.

Just used the carbtune on a 79 Special. They synced correctly. There are no broken hoses on the tool. The rubber carb mounts were replaced by PO. All carbs respond to idle air/fuel mixture screws. But I have to be missing something?????

MP

[bikerphil]

When you have all 4 reading equal and the idle rises, did you try turning it down with the master idle control knob at the front bottom of the carbs? Just because the PO replaced the carb manifolds doesn't mean they were installed correctly, JAT

[CaptonZap]

Have you checked the valve clearances before trying to sync?
Have you checked compression?
Are the float levels equal?
Idle screws equal? I adjust them in until the RPM's start dropping, back them out a half turn, and go to the next one. Set the idle down, then go back to the carbtune, and sync the pairs.
Go through the idle needles one more time, then sync again, and you should be there.
CZ

[MPittma100]

Carb Sync Issues

I reapproached the bike today and tried my luck again with the carb sync. I did find where the problem is, but have not fixed it yet. I did get the columns closer.

The problem seems to be with the linkage of the carb(s). When I turned the screw between 2&3 to bring all four columns together, it started idling higher the more the screw was turned. This I take as a normal condition. So the next step would be to set the idle with the main idle screw.

This is where the problem lies. This screw can be backed completely away from the lever and the idle stays at 1100-1200. I can take a screw driver and push down on the lever that has the throttle cable attached and it will idle down some doing this. As I let it go, the idle goes back up. There is slack in the cable. So the cable length is ok.

In conclusion, I am thinking that the carbs will have to come off to be able to determine what is actually wrong. When I do that, I will report the findings here.

Thanks for all of your input.

MP

[jetmechmarty]

Mike,

That's the same issue I had. I remove the carbs and did a proper bench sync. That fixed it.

[MPittma100]

Bench Sync

I have not done a bench sync before. How is that done? Is there a link here?

MP

[jetmechmarty]

I have not done a bench sync before. How is that done? Is there a link here?

MP

Easy Bench Sync Method