Carburetor Synchronization (long) with Pictures

[Oyeaa]

While I was de-smogging and installing the cruise control I wanted to make it a little easier to synchronize my carbs.  I hate trying to reach in between hot carbs and connect and disconnect vacuum lines temporarily just to do a sync.

So when I pulled out all the desmog stuff I also removed the carb drain lines and the drain line manifold (mostly because I could not find a 6 port manifold with the correct size nipples at any of my local auto parts stores).

I plugged the big hole in the end of the manifold and connected 6 vacuum lines to each of the available ports and I numbered them 1 through 6 and routed them from the cover just in front of the tank on the left hand side of the bike to each carb.  Then at each carb I installed a vacuum check valve in each of the 6 lines.  I put a couple of t connectors in the #3 vacuum line and routed from them one tube to the petcock and the other tube to the cruise control vacuum chamber.  I could have connected the petcock and the vacuum canister to any of the 6 lines as this connection is on the manifold side of the check valve and is effectively connected to all 6 carbs as a result.



Check Valve:

I used some from auto zone Help part number 47149 but any generic check valve should work. 

Make sure that the vacuum side is pointed towards the carburetor. To check this, you can blow through one end of the valve. If the air flows freely, you are blowing in the supply side (should be pointed towards the canister). If the flow is blocked, you are blowing in the vacuum side (should be pointed towards the carburetors).
The black end of this check valve is the vacuum side (point it towards the carbs), and the white is the supply side (point it towards the vacuum canister).
Since the diameter of the white end is smaller than the black end it needs to have heat shrink tubing applied to build it up a little.  The check valve now fits tightly into a 5/32 vacuum hose.To make sure that I got a tight seal I carefully applied a little glue to the barb and also put a clamp around the tube.



Once everything is interconnected it is pretty easy to perform the  :)procedure.

1.  Remove the carburetor link covers and the frame cover to expose the carb vacuum lines and the manifold.

2.  Disconnect the carb #3 line from the manifold and put the twinmax carb balancer in between the manifold and the #3 carb. 

3.  Pinch off all 6 lines using hemostatic clamps.

4.  Start engine and allow it to warm up to normal operating temperature and check that it is idling at 800-1000 RPM.  Adjust the idle speed by adjusting the throttle stop screw.

5.  Sequentially remove and replace each of the other cylinders one at a time.  As each clamp is removed the meter will indicate the difference between the non adjustable reference #3 carb and whichever other cylinder is not pinched off.

6.  After all 6 are compared the carb that is the farthest off from #3 should be adjusted first.

7.  Unclamp the carb vacuum line that is the worst and adjust the appropriate carb by turning the adjusting screw for that carb until it is balanced with #3 carb.

8.  Rev the engine a couple of times and recheck the idle speed is still 800-1000 RPM and the unclamped carb vacuum difference and adjust it as needed.

9.  Recheck all carbs by sequentially removing and reinstalling each of the other clamps one at a time.

10.  Repeat steps 6 through 9 as needed.

11.  Install the carburetor link covers.

12.  Remove the twinmax carb balancer and reconnect the carb #3 vacuum line to the manifold.

13.  Tuck the manifold and vacuum lines into the frame and put cover in place.


http://s164.photobucket.com/albums/u11/VALKYRIEINTERSTATE/Carburetor%20Synchronization/

[DFragn]

Nice write-up 

I noticed your check-valves are within an inch or so of the intakes. I would recommend moving them out and away 4 - 6" min because fuel does consistently track out into the vac lines 4+ inches and it will eventually foul most check valves, especially the ones you are using.
If your cruise slowly begins slow it's function and finally stop working the culprit will likely be the fouled check valves.

Just my experience and 2 cents. It took me a while to figure out what was happening until I did a carb sync with clear hoses and witnessed the fuel back flow. It's very light but enough to foul check valves in time. It can grunge up the internals of the check valve much like a leaking intake o-ring on the head does.

[Oyeaa]

Thanks for the heads up.

[John Schmidt]

I use the Twin Max, have a single hose running to a manifold with five small petcocks on it I picked up at PetSmart. They're used on fish tanks. Hook the base hose up to #3, and the other five to the ports in back of the carbs. I just use some long needle nose pliers and only install them one time for the sync job. I lay the TwinMax on the seat and open each petcock, one at a time. No need to pinch off any vacuum lines, just open the petcock you want to check/adjust. If you happen to be doing it to a bike with a vacuum operated fuel petcock, I start the bike, use the hemostat to pinch off the #6 hose, then install the gauge hose on it. No big mess of hoses left in place when I'm done and I can do every one just by opening the small petcock. I don't have a picture of it but if somebody wants one, I'll take a shot of it tomorrow.

[Ricky-D]

I don't feel check valves are appropriate when synchronizing the carburetors.

Reason being that the vacuum cannot readjust when adjusting the individual carburetor screws.

***

[Oyeaa]

Have you tested this theory?  It does sound like a very good theory and I suppose that I would even tend to agree with that theory. 

But, every time I have used this setup and turned a carb adjustment screw I have gotten an immediate change in the twin max reading regardless of the direction that I turn the screw.  Sometimes (usually) I even forget which way I need to turn the screw and I see the meter change for the worse and know that I got the adjustment wrong so I back it up the other way and the meter then responds appropriately.  Also as I pinch and un-pinch and re-pinch the various carbs vacuum lines I get a meter change that is repeatable for each the the various carbs.  Perhaps it is not as drastic as others may have seen because the check valves act as a dampener of sorts "maybe" but I have good repeatable results.  Just to be sure I went through the process and actually vented the #3 vacuum line and then each of the others one at a time as I cycled through the other 5 by pulling the lines off the bottom of the twin max and then reconnecting them and the readings that were obtained without "Breaking Vacuum" and after "Breaking vacuum" were the same.  Then I was concerned that perhaps I had a leak.  So I drew vacuum on the whole setup and it holds vacuum. 

I still think your theory sounds very reasonable and I am not sure why text book physics do not apply in this case.  Thanks for the help though you really made me second check all my stuff and validate the set up is good.
 

[Ricky-D]

Here's what I have used to synchronize my carbs.



Have to snub each line to get a steady and uniform needle response.

Adjusting one carburetor affect all other carb settings, which is easily detected on the gauges.

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[Oyeaa]

Nice looking set up.