Cannot Sync Carbs 1 & 3

[jrp]

Hey all,

I'm sort of stuck here and am looking to the collective wisdom of the forum for some assistance.

Recently rebuilt a set of ST1100 carbs that I picked up off Ebay from a breaker and assembled the rack today.

Proceeded to do a bench sync and discovered that I could not get the butterflies on carbs 1 & 3 to line up, even when going to full adjustment on the sync screws.

Pictured here are carbs 1 & 3. You can see that the butterflies are not lined up. Suggestions?

 

[bdalameda]

Did you remove the butterfly valves from the shafts? Some butterfly valves on the edges are cut at angle to fully seat when fully closed. If the butterfly valve was installed backwards the valve will not close correctly. I’m not sure if the ST carb valves are made this way or not.

Dan

 

[jrp]

Did you remove the butterfly valves from the shafts? Some butterfly valves on the edges are cut at angle to fully seat when fully closed. If the butterfly valve was installed backwards the valve will not close correctly. I’m not sure if the ST carb valves are made this way or not.

Dan

Hi Dan,

I did not remove the butterfly valves. I removed the sync screws and springs just to make sure that the valve on #1 closed normally and it did. I'm stumped on this.

 

[D_W_L]

It appears to me that that #1 carb's butterfly is binding. I would suggest 'decoupling' the carbs and checking to see if the butterfly can freely seat into the closed position.

 

[jrp]

It appears to me that that #1 carb's butterfly is binding. I would suggest 'decoupling' the carbs and checking to see if the butterfly can freely seat into the closed position.

Thanks for the suggestion. I had the carbs separated when I cleaned them. No problems with the butterfly seating.

 

[Igofar]

Loosen the screws on #1 and #3 and check for binding.
Don't tighten one side at a time, but all together in a pattern over several times.

 

[TerryS]

Would this have anything to do with the relative position of the carb bodies to each other? I.e when you reassembled them onto the trumpets/plenum, I recall there are screws that can be loosened to assist with fitment. Perhaps try loosening these off again, and seeing if the throttle plate alignment also changes.

 

[jrp]

I removed the sync screws and springs on #1 and #3. No binding. Here is a video:

The problem is that the sync flange that is on the end of the butterfly valve on #1 rotates down too far. Or maybe #3 is too high? The #3 valve shaft has a nut on the end of it (see picture below). Could this be for adjusting the position of the sync flange?

 

[Bmacleod]

That nut just holds that sync plate/throttle linkage on the end of the shaft. the plate looks "keyed" to the shaft (take note of the "flat" that is milled into the shaft) and you shouldnt be able to change the plate position. I think you are trying to get both sync plates looking level with each other when in fact you should be setting the screws to mimic the closed positions that are present in the vid. Try turning #3 CW and #1 CCW until the throttle plates look right. If that is wong, try the other way. The carbs are upside down and its getting late... I could have that backward, but you get what I am saying, right? In the first post, you say that even with the screws at max they wont line up, but it looks like there are 2 different size springs. You may have to stagger the springs to allow the adjustments to go further. e.g., if you need to take #1 further but the spring is fully compressed and it is the spring with more coils, you likely have to put in the shorter spring. It looks like each side will require a short and a long spring. In your first pic you have both long springs on one side and both short springs on the other side. One side will have limited adjustment.
Disclaimer: I say that one spring is long and one is short. That may not be true, they may just be different tensions, but you get my drift

 

[jrp]

That nut just holds that sync plate/throttle linkage on the end of the shaft. the plate looks "keyed" to the shaft (take note of the "flat" that is milled into the shaft) and you shouldnt be able to change the plate position. I think you are trying to get both sync plates looking level with each other when in fact you should be setting the screws to mimic the closed positions that are present in the vid. Try turning #3 CW and #1 CCW until the throttle plates look right. If that is wong, try the other way. The carbs are upside down and its getting late... I could have that backward, but you get what I am saying, right?

Thanks for the reply. I don't care if the sync plates are level with each other. The problem is that I cannot get things aligned within the range of the adjustment. I'll post another video illustrating that when I get a chance.

 

[CruSTy]

I removed the sync screws and springs on #1 and #3. No binding. Here is a video:

The problem is that the sync flange that is on the end of the butterfly valve on #1 rotates down too far. Or maybe #3 is too high? The #3 valve shaft has a nut on the end of it (see picture below). Could this be for adjusting the position of the sync flange?

I'm not familliar with these carbs but could 1 & 4 or 2 & 3 carbs be swapped inadvertently during assembly

 

[jrp]

I'm not familliar with these carbs but could 1 & 4 or 2 & 3 carbs be swapped inadvertently during assembly

Good thinking, but these only go together one way.

 

[jrp]

So after taking my working set of carbs and putting them on the bench next to these, I am slowly coming to the realization that this carb assembly took a really good shot at some point after being taken off the bike and shipped to me and that one or more of the linkages were bent (specifically, I noticed a slight bend in the shaft that the on #3 that the throttle link attaches to). When the carbs came to me, the air chamber/duct assembly was not connected to the carbs. Without it, the carbs were only held together by the throttle link and the choke valve link and the carb connecting screws were loose. I suspect it fell off a workbench. It was well packaged when it arrived so I doubt it happened during transit.

So these go back on the shelf until I get the time and motivation to take it all apart (again) and see if I can straighten things out. We've been getting some days here in the 60's and low 70's and I want to get everything back together and go riding!

Thanks for the all the replies.

Jeff