Topic: $10 home made carb sync tool

[Psychonaut]

I finally got tired of the not as smooth as it should be idle. I'm too frugal for real gauges if I can save a buck and get the same results. Hopefully this inspires someone else to make one. If you don't have a drill press you can buy just the screws onlne.


5mm x .08 x 20mm screws or maybe they were 16mm long either way I should have bought 25mm ones. I drilled them with a 1/16" bit and cut the heads off, locktighted the nuts on and put small O-rings on (R-01).









1/4" drip line T's.







I drilled and tapped a hole in the top of a 2 liter for an 1/8" fitting. Safety first






I used a 20' pack or 1/4" clear tubing mounted on a peice of scrap wood.
Filled with 80-90w gear oil. There is about 10" of oil in the lines.


This is after about 30-60 secounds at idle. When I started 30 seconds would have completely emptied 2 and 3.

[Brantley]

Kudos. I LIVE for this stuff. To me making your own tools is equal to sticking it to the man. If you've got a boneyard near you drop another $10 on a small dirtbike tank to make a baby bottle and get rid of that 2 liter.

[Tews19]

Freaking cool, can you make a video with it on the bike and running ?

[Deltarider]

How about bouncing? Did you need any restrictors? Or did the thickness of that oil do the trick?

[Tugboat]

Nicely done!!

[Psychonaut]

How about bouncing? Did you need any restrictors? Or did the thickness of that oil do the trick?

The heavier oil took care of the bounce. I tried something lighter oil initially but it was impossible to let the bike run for more than 3 seconds. The thick oil moves slow enough that you have some time to adjust while running.

[stampederunner]

With the tubes not being straight wouldn't that make the tubes different lengths and throwing off your readings? I tried making one like yours and couldn't get steady readings. I then tried a bottle type manometer and it was so easy to use and cost nothing since reused the hose from my previous manometer experiment. http://faq.ninja250.org/wiki/How_do_I_synchronize_the_carburetors%3F Check this out about half way down the page.

[nayto550]

With the tubes not being straight wouldn't that make the tubes different lengths and throwing off your readings?

Fluids don't care about the length or bends in the tubes (as long as it's not kinked).  Manometers measure pressure differentials by vertical distance only, horizontal distances are completely irrelevent.

I built a similar carb sync, but I have problems with fluid bounce.  Mine has ATF in it, I'll have to give the heavier gear oil a try next time I use it.

[iron_worker]

Are all the lines linked together at the bottom? I think this is a problem... this way you have one cylinder pulling a vacuum and drawing the fluid up but that has to draw the fluid from somewhere ... in this case it must come from one of the other lines. So the vacuum you're measuring is actually the difference between cylinders.

I would connect a 5th line that does not get connected to any of the carbs but only serves as a vent to atmospheric pressure.

IW

[ACVWguy]

So the vacuum you're measuring is actually the difference between cylinders.

I would connect a 5th line that does not get connected to any of the carbs but only serves as a vent to atmospheric pressure.

IW

Measuring the vacuum difference between cylinders is the purpose of carb synchronization in the first place. By the design of these fluid manometers, if one fluid level rises, all the others must drop (all other things being equal). This makes the adjustment much more touchy, but also more accurate. Adding a vent to the atmosphere defeats the entire purpose of a manometer. A vent would allow air to enter the system and foam up the fluid, skewing the readings. But that wouldn't matter because by that time, the fluid would have been sucked right into the vacuum ports.

I tried making a manometer like the OP's, but I used ATF as a fluid. ATF is much more thin, so it bounces up and down in the manometer at idle and foams up in seconds. Then it takes several minutes to an hour for the ATF to settle down level and release all of the bubbles. And at that time, my carbs were so far out of sync that one or two cylinders just sucked all of the ATF into the engine. I just went down to HF and bought two vacuum gauges and hooked one to cyl #1 and synced #2 with #1, followed by #3 and #4, always leaving one connected to #1. Takes time but it's accurate. And I only payed $22 for the gauges. Just another option.

[iron_worker]

Hmmm I suppose you could be right. It could make the manometer over sensitive. I suppose the true purpose of synchronizing carbs is to make the difference in vacuum readings = 0. The actual vacuum amount is not really relevant.

IW

[CB500_k2]

That is a great design.  I never really was comfortable with having a bottle of mercury in the garage.  You have a spill and the result is a toxic area for a long time.  Looking at relative pressure rather than absolute using a lower density fluid should allow for a pretty precise setup of the carbs.  I like the use of a higher viscosity fluid to damp down the fluctuations.  I am going to make one today.  Thanks.

[ACVWguy]

Hmmm I suppose you could be right. It could make the manometer over sensitive. I suppose the true purpose of synchronizing carbs is to make the difference in vacuum readings = 0. The actual vacuum amount is not really relevant.

IW

Exactly. All you need to do is make sure that each cylinder is drawing the same vacuum. That's synchronization.

[mono]

this is way too cool.  great job!   i read something on this forum that makes me feel dumb almost every day, and i love it because sometimes the answers are sitting right there in the garage just waiting to be found 

[stampederunner]

To anyone considering building their own manometer I really would try the two bottle manometer. I just used 2 Snapple bottles and drilled 2 holes in each lid. You then make a transfer tube that goes through the lid to the bottom of each bottle. Then you put your vacuum line barely into the lid. Then you fill one bottle almost to the top, then suck on the empty bottles vacuum line to get a little fluid in the empty bottle. Hook it up to 2 carbs and the stronger carb will slowly pull more fluid through the transfer tube. Once the carbs are pulling equal amounts of vacuum the fluid will be level in the bottles. The fluid does not bounce at all and there is zero risk of anything being sucked into your carbs. Also it stores neatly in a cabinet for later use.

[bjatwood]

What happens to the sync of the first 2 carbs when you adjust the other two carbs? My vacumn changes on all the carbs whenever I adjust even 1 carb a bit......

[Psychonaut]

ATF is round 5-10w. It does not bounce at all with the gear oil, they only movement is from the carb with high and low vacuum and it is slow enough that you have time to adjust. In 3 seconds I had ATF at the carb. The gear oil does not separate at all. The only way to get air under it is to pull all the oil through that line.   I'm sure the bottle method works but with the heavy oil the 1/4 line works pretty good and is easy to make.

What happens to the sync of the first 2 carbs when you adjust the other two carbs? My vacumn changes on all the carbs whenever I adjust even 1 carb a bit......

The oil will move up in the line with the carb with the highest vacuum. The carb with the lowest vacuum  is going down. My carbs where way out of wack. but with in a few turns they were pretty close. I mess with them for maybe 5 minutes until they were perfect.

[adamlwvdc36]

This is an absolutely awesome design... as an engineer I would only recommend one thing to be added:  a 4 pack of 1/4" barb plugs... for storage.  then it would be perfect.  you could always drain the system when not in use... but i think this would probably get tiring after the 4th time filling it... maybe not. science is cOOOl!!!

[flopshot]

Thanks Psychonaut, your post inspired me to build on of my own.

it's color coded, fills from the bottom reservoir and each tube is mounted over a yardstick.   the ATF was a little sensitive so i went with a 50/50 mix of ATF and 30w motor oil.

[PurduePete]

Thanks Psychonaut, your post inspired me to build on of my own.

it's color coded, fills from the bottom reservoir and each tube is mounted over a yardstick.   the ATF was a little sensitive so i went with a 50/50 mix of ATF and 30w motor oil.

Well you went all out. That looks good. I was trying to figure out how to make a reservoir at the bottom for one when I make it. After parts get in this coming week and I finish that up your design is next on my list. Imagine for someone creative there is a way to make a 2 bottle design into 4 bottle design with pcv pipe and fittings. Would be tricky but could be a lot of fun to design. Do like the idea of just watching fluid level in the bottle and not worrying about having it sucked up into the engine. Might model something up and see if anyone thinks it would work on here.

[PurduePete]

This is what I came up with. It is my version of the 2 bottle system for a 4 carb bike. Because fluid is shared among all four bottles pressure increases from one will affect the level of fluid in all bottles. Once they are in sync the level will be the same. It should have no problem working and completely eliminate the issue of sucking fluid into the bike. Also because of the design I believe that a light weight fluid such as water would actually work the best. Would still not suggest using water but just a really light weight liquid. The taller the tubes the safer your system is. In the picture the tubes are 6 inches tall. If you made them about 18 inches tall or so and then added enough fluid to fill each tube to about 3 inches that should never allow the fluid to reach the top of the tubes if one was really out of sync. I would say that some thicker tubing might even work. Lots of options but this is the route I will be going. Let me know what you guys think of my idea here. Might not even be new, really just a larger version of the reducers, much larger.

[MattFreeman]

Very Cool

[Duke-Nukem-Dan]

Old post but good topic. If anyone has had problems with their fluid foaming up or getting air bubbles with the long tube setup, do what I did. Take it off real quick then swing it around as fast as you can. Voila, all the fluid is air free and equal. You might look like an idiot but who cares, your coolness will even out after you ride your bike. My carbs were way out of sync so they foamed up quickly.

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