What is the correct carb sync order? 81 XJ 550

Could someone please enlighten me on the correct carb sync order?

 

The running sync - the #3 carb is considered non-adjustable.
You sync #4 to #3
You sync #1 and #2 together
Then, you adjust the 1-2 set to #3

However - the bench-sync is a bit different. (non-running)
I use 2 layers of printer paper that are cut to look like feeler gauges.
It's 0.010 inch thick when stacked.
Make sure you have some additional clearance on 1,2, and 4.
Adjust #3 with the idle screw until the paper gauge just drags thru with some resistance.
Adjust #4 next
Adjust #2 next
Adjust #1 ~last~

Re-check and fine-tune

 

So the #2 screw controls carbs 1 and 2 together? and which ones do you read vacuum on while syncing 1,2 to 3,4?

 

it's like this.

1 leans on 2, which leans on 3. if you move 2, 1 will move with it, because it is leaning on it. 4 also leans on 3, because 3 is the "baseline" carb.

is that clearer?

as far as vacuum, they all need to be the same. you should have some type of vacuum gauge hooked up to all four at once to get an accurate reading -- it doesn't matter what the reading is, as long as they all match.

 

So basically you need a minimum of 3 vacuum gauges. I have a set of 4 on a manifold but someone dropped it and one is not so accurate anymore. Whoops

 

there are instructions around here somewhere on how to make a 4-tube liquid gauge out of 20 feet of aquarium tubing, a 4-way Tee junction and some transmission fluid. works as well as anything, just gotta keep the tubes straight.

 

Here's some further reading

http://xjbikes.com/Forums/viewtopic/t=2 ... =sync.html

 

There you go.

You DON'T have to have all 4 hooked up together (although it does make it a damn sight quicker and much easier.)

If doing a "two-bottle comparison" (or vinyl tubing) you would compare #4 to #3; compare #1 to #2, and adjust accordingly; then compare #2 to #3, since #2 drags #1 along with it. To then double-check that adjustment, you can compare #1 to #3; but the adjustment of the 1/2 pair to 3 is made with #2.

You can even use a single vacuum gauge and record the readings on each but it's VERY time consuming that way.

Be sure you've correctly blocked your YICS too.