Manometer idea for carb sync's

OKC

I think that the pressures would average out which in turn will give you a false reading.

here is an example: say proper pressure is 30 psi. and you are going to test 3 carbs. carb 1 has 90psi, carb 2 has 0 psi and carb 3 has 0 psi. the average will be 30psi. which is the proper pressure, but obviously carbs 2 and 3 are completely messed up.

but maybe im wrong, just my opinion.

If you want to sync all of your carbs at one time, i would have four seperate hoses each going to one carb. collect the unconnected hoses and fill each tube so they are all at equal heights. then start the bike and adjust three of the carbs to a single carb. i dont know how precise this procedure would be, but it will make all of your carbs have equal pressure.

buzz

Since the reason to synchronize carbs is to adjust one carb so that it has the same vacume reading as the one next to it, why in the world would you want to hook four of them to one gauge? How would you compare one to the other?

If you have a gauge like the one pictured above, you do #1 and #2 carbs, then you do #3 and #4 carbs, then #2 and #3, and you are done.

I tried it. I took the yardstick, 4 long long pieces of clear pvc tubing, and used some tee connectors to connect all the tubes together at the bottom of the yardstick. Looking in my garage for a heavy fluid, I used 85W140 gear oil.

If you have a 4-way tug of war, if one side is winning, it is at the expense of the other three. To reconstruct buz' example, if the vacuum level at the 4 carbs is 20,15,40,20 then #3 will be rising and #2 will be falling. #1 and 4 MIGHT fall at a lower rate.
Its a 4-way differential manometer.

The tube connected to the carb with the higher pressure doesn't HOLD a higher level; it is sucking fluid up at a rate greater than the others, its fluid will keep rising and you'd better adjust it before it reaches the top.

Did it work? I dunno! I think it did. I was eventually able to get all 4 tubes to balance at the same level, and the bike ran fine, but it still needed rings in the #2 cylinder. I bought a motion pro kit to re-sync with when I get my jugs back and reassemble. The tube of mercury that came with it is one of the coolest things I've ever seen.

Now, in reality, you don't really need more than 2 vacuum connections. sync 1 to 2, sync 3 to 4, then connect to 2 and 3 and use the adjuster in the middle to sync one side to the other.

Rickman wrote:

Now, in reality, you don't really need more than 2 vacuum connections. sync 1 to 2, sync 3 to 4, then connect to 2 and 3 and use the adjuster in the middle to sync one side to the other.

The "adjuster in the middle" you mention, are you speaking of the big knob to adjust the idle speed?

This is all just a big dynamic circuit problem.

Put adjustable restrictors at the tops of the columns. Hook all four hoses to one vacuum source with a big 4-1 manifold (available at any auto parts store and most hardware stores). Adjust the restrictors until you get the same reading on all four tubes. Simple. This calibrates the tool.

Now ditch the 4-1 manifold and hook the four tubes up to your engine and adjust the carbs until the tubes match. (Blip the throttle often during the adjustments to get a good average reading. Sometimes some will read higher then after a blip it may read lower. You want to average it out.)

The restricors can be anything you can put in-line of the hose and poke a pin-hole through. To calibrate it, you poke the hole a tad bigger on the ones that are reading low. That's the same way the mercury ones work. The restrictor is important because the vacuum is in pulses. The restrictor, plus the volume of the tube smoothes out the pulses.

You can put the restrictors anywhere in the hoses, but the volume of air between the restrictor and the water must be the same. Ideally, all four tubes should be as identical as possible.

I don't like swapping tubes back and forth. Use four tubes! The readings must be made simultaneously. Even the slightest change in conditions can change the vacuum readings off, so you don't want any time-laps between readings. All four should be read at once.

Post edited by: loudhvx, at: 2006/05/03 18:11

del

I saw this on anoither site. Use a "T" to connect all 4 tubes.

Nice pic ChurchBuilder!
Well, I think the picture clears it up for me. Now that I see a picture I believe that joining all 4 hoses together with a 4-way union is not needed. As long as you can see all four tubes and adjust the carbs until they all have equal height, you should be good. The tubes would need to be the same length, and have the exact same amount of fluid.

Now the big question.... In adjusting the vacuum between two carbs, do you adjust the lower reading carb or the higher reading carb, because you'll only need to adjust one carb...and is it better to have all 4 carbs set at a higher vacuum reading or a lower reading?

NormZ wrote:

I use the homemade manometer you're referring to sync my carbs 2 at a time. Works well but takes three steps (sync 1&2, then 3&4, then 2&3).

This confuses me. You set 1&2 so they read the same. For this discussion lets say '20'. Then you set 3&4 the same, but they happen to be '25'

Then you set 2&3, so those two happen to meet at '22.5'. That's the three steps...

Don't you then have to go and do it all over again to get 1&2 equal, then do 3&4? And it seems like they would still be off. Am I missing something?

when you adjust 2&3 3&4 stay together and 1&2 stay together

OKC_Kent, if you look at the actual linkage on the carbs I think it will be easy to understand.
It's one of those things that's hard to explain, but obvious when you look at it

I don't like the fact that it looks like it's a "differential pair" manometer rather than one using atmosphere as a reference.