Alternative Homemade Carburetor Sync Tool

[FirstYearDeek]

This post is a collection of several posts from this and another board; I have some experience with this instrument used to synchronize exhaust feeds in a piece of automation at work... I never thought to use the same method on an engine, due mostly to the lower vacuum.

jap4lvr from Lincoln, NE brought it to our attention in this post; I felt I could lend my illustration skills and some theory so I'm presenting it here in the How To section.

Do-It-Yourself Synchronization Tool

Preparation
Parts you will need:
4 identically sized glass or very rigid plastic containers
4 rubber or gum stoppers
10 feet of stiff, clear tubing, 1/4" ID
4 Intake runner adapters

...McMaster Carr and Fastenal (possibly others) sell vented cap-head screws. These 4 or 5 mm machine screws have a 1.5mm hole from end to end. Just screw 'em in and slip the hose over the head. (Hot water and lubricant will help with this)

Tools you will need:
3/8" drill bit and drill
Pliers
Non-petroleum lubricant (KY or vegetable oil)

Constructing the Apparatus
1. Drill holes in the rubber stoppers. Two of them need two holes, the other two need 3 holes.

...freezing the plugs to make drilling the holes easier and more acurate...

2. Cut the tubing up. You need three lengths of tubing long enough to reach very close to the bottom of two bottles with a generous loop above the stoppers. The remaining length should be cut to four EQUAL lengths.

3. Insert the tubing. Use your lubricant and pliers here. The two-holed stoppers get one long hose and one end of the transfer hoses. The two three-holed stoppers get one long hose each and the other end of the transfer hoses in the two-holed stoppers. The third short hose goes in the remaining hole in the three-holed stoppers. (See diagram... this is much simpler than it sounds)

4. Fill one of the bottles to near the top (not all the way) Then distribute this volume of liquid to the three empty bottles so each has 1/4 of the original volume.

5. Stopper the bottles and arrange as seen in the diagram.

...I could never get any bubbles to flow through the tubes at the top unless I was very near emptying one of the bottles and beginning to draw air.

6. To get bubbles in the line, suck on one of the long tubes and shake the container. This should introduce fluid and air, making bubbles.



Using the Sync Tool

1. Attach the hoses to the intake runners as labeled above.
2. Start the motor.
3. You should see the bubbles moving in the loops. (Unless you're bike is already perfectly synced!)
4. Start with 1/3, adjust until the bubbles aren't moving between container 1 and 3.
5. Move to 2/4. Adjust until the bubbles aren't moving between container 2 and 4.
6. Move to the side-to-side adjuster. Adjust until the bubbles aren't moving between container 3 and 2.

When all your bubbles are stationary, you're done!

You shouldn't let the level of any one bottle get lower than half of that of the one next to it. If that happens, kill the bike, uncork the bottles and re-distribute the fluid.

You can prevent fluid from being sucked into the motor by ensuring the long tubes don't extend into the bottle. Only insert them into the stopper until they reach the inside surface.

Theory of Operation

Fluid moves between containers due to the varying vacuum levels in the airspace above the fluid. "Nature abhors a vacuum" and an equilibrium is sought by transferring air from one container to the next. There's fluid in the way so you get to see the air move from A to B.

If you had a very poorly synchronized rack and let the motor run for a time, you would eventually transfer all the fluid into one (or two) of the containers, leaving the other three (or two) empty.

Advantages over a manometer
1. Providing your long tubes do not protrude into the bottles too much, it's nearly impossible to suck the fluid into your cylinders.

2. Any fluid can be used, within reason.

3. Pulses are less visible due to the dampening effect of the airspace above the fluid in the containers.

"...This never needs any calibrating either.

4. ^^ Simply ensure the fluid and air paths are clear of restrictions and each of the four containers will react identically.

Disadvantages

...It does not measure absolute pressure... It does measure differences in pressure, and that's what we want!

1. Tom E is quite right. The absolute vacuum level is less important than the balance between the carbs. (Assuming, of course all the other motor conditions are fine... compression, timing, etc.)

2. Side-to-side (1/3 vs 2/4) balancing isn't quite as accurate as a 4-gauge system; the effect of 1 and 4 on the balance is diminished since it's two air spaces from the transfer tube. BUT as long as the 1/3 balance and the 2/4 balance are good, the 3/2 measure you're making is still meaningful.

...I couldn't adjust them fast enough to prevent one or two of the bottles from being emptied and another over fill to the point that the liquid, water in this case, was being sucked into the engine.

3. Wide-open tubing will cause very fast vacuum changes and differentials between cylinders may result in transfer of fluid well before you have an opportunity to make an adjustment. Putting a restriction in the long tubes will slow this down. Just be sure to do it the same on all four tubes.

[EDIT] Added advantage from jap4lvr [/EDIT]
[EDIT] Added some information from Sage's post[/EDIT]

[jap4lvr]

Looks great. Thanks for writing this up. Looks better than my 5 minute MSpaint picture and my attempt at an explanation for building it.
This stuff all makes sense in my head but getting it out is the hard part.

[jap4lvr]

I will add that this method is very accurate.
You may find that you can never actually get the bubbles to stop. You just have to get them moving as slow as you can because the gauge is more sensitive than the adjustment screws on the carbs


There shouldnt be a difference in the accuracy of the measurement between the 2 sides I dont think. The level in bottle #1 also depends on #2,3,and4. So if bottle #4 was really off it would be hard to adjust bottles #1 and #2, but you would see that #4 was really off because the fluid would be flying through that loop. They are all dependent on each other. But once you get them pretty close the error is negligibly small.
Correct me if I am wrong here.


This never needs any calibrating either.

[FirstYearDeek]

The notion that the sync between 1/3 and 2/4 can't be as accurate as the pairs themselves is one that's mentioned in the literature for the device we use at work. That device, however, operates on much less vacuum and is prone to leaks in a way this one is not.

That's a good point about calibration; I'll add it to the advantages list!

-Deek

[Roady]

Fantastic. I've already got lots of tubing from my failed manometer and can put this one together quick. Except, I'll need to empty four Tangueray bottles! That may take a few minutes.

Excellent job, jap4lvr and well put together, Deek. Off to ShopTalk for this one.

[Sagebrush]

I made this unit just like the picture with four Snapple bottles. I hooked them up to the carbs after warming the bike but I couldn't adjust them fast enough to prevent one or two of the bottles from being emptied and another over fill to the point that the liquid, water in this case, was being sucked into the engine.

Well, I reduced my "gauge" to just two bottles and sychned one cylinder at a time. After playing with the adjustments for a while I finally figured out how to accomplish my goal.

I could never get any bubbles to flow through the tubes at the top unless I was very near emptying one of the bottles and beginning to draw air. So I arrived at the solution of watching the level in the bottle. You only have to watch one. If the level changes at all then there is a vacuum differential between the cylinder that you are adjusting and #3.

I also found that very tiny adjustments had a large effect. I discovered that turning the adjustment CCW will cause the water level to rise in your bottle and inversely adjusting it CW caused the water level to fall. After some time the water level either got too high or too low and I discovered that I could reset the levels by either gently prying up on the tab that the adjustment screw was in or press down on the adjustment screw and this would allow me to equalize the levels in the bottles without changing the setting on the screw itself.

Furthermore after making an adjustment, particularly if you are close to equalibrium, I found it best to blip the throttle to take out any stress in the linkage that may have been introduced by the pressure of the screw driver on the adjustment screw and allow the level to settle out for a minute or so.

Once I figured out these things it became very easy to adjust them. I found the hardest thing was tightening the lock nut on the adjustment screw without disturbing the adjustment. That part takes a little practice.

One more thing, as you get closer to getting your carbs synched you may find that the idle begins to smooth out and actually get faster. I found I had to adjust my idle setting back to 1k RPM a couple of times during this procedure.

Overall, I found this to be a very accurate and relatively easy method of synching my carbs and I'll tell you this my yellow 1100 has never run so good. Its amazing the power increase that I'm now enjoying.

[Roady]

Great info, Dean.

Thanks for all of the minute details, that's going to help me out (if I ever get to it on the bikes ).

[Sagebrush]

Great info, Dean.

Thanks for all of the minute details, that's going to help me out (if I ever get to it on the bikes Smile ).

I actually had fun doing it, wish I had another one to synch up . Hey Sgwilly, does your bike need the carbs synched?

[jap4lvr]

I would imagine that the water would suck through pretty fast. I think I am running 50 weight oil in mine.