Can I make homemade carb sync tool?

I was just looking at carb sync tools and ran acroos this:

http://www.powerchutes.com/manometer.asp

It's basically a recipe for a homemade device; get a long PVC tube,
make a U out of it and attach it to a yardstick. Fill partway with
oil, then connect to 2 carbs to sync them.

I'm curious if this would work. My first instinct is that the pressure
differential between carbs would suck the oil into towards the
more-vacuum carb and into the carb itself (which would be funny, but
not useful I'd imagine). But is it the case that there's usually such
a small vacuum differential that it will only "lift" the oil towards
one carb but not suck it out completely? I'd love to try it, as it
seems like a fun project, but I'm just curious as to the theory behind
it. Also; would sucking a bit of motor oil into the vacuum port likely
harm a carb? (in the case that it does have enough vaccum to suck oil
out of the tube).

Also, could I just get a pair of automotive MAP sensors (manifold
absolute pressure, digital pressure guages), hook them up to a display,
and just sync on that? Are they accurate enough? I think they
normally work up to 24 psi or such. Could these be connected
"backwards" to measure vacuum instead of pressure? Sorry if these
questions don't make sense, I'm curious but in a hurry and out the
door. Any comments, corrections, links, experiences welcome. Thanks.

 

In my Clymers for the Old Honda 750 there is a rather detailed set of
instructions and drawings for a do it yourself sync tool. Uses baby food
jars and scrap lumber. Looks like something out of a 1950's Popular
Mechanics. (It does work, too.)
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Mark,
Thanks so much for the reply. I've been really wanting to sync the
carbs, but have hesitated buying a carbtune (or similar). I think I'll
try this method first. I've got an inline 4... so I'm guessing I could
use 2 tubes, one for 1 and 2, the other for 3 and 4. Once both
cylinder pairs are synced, then connect 2 and 3 (or 1 and 4) and sync
that?

One problem is the vacuum adapters (don't know the name). I've got 2
cylinders with vacuum lines coming out (fuel pump, vacuum operated fuel
petcock), and two with screws. For the screws, what could I use to
attach a hose to? Is there an easy way to make/get an adapter? I know
the carbtune kits come with those.

GC, I'd love to see that tool. I love (obsess over) DIY tools,
especially the very cheap/convenient and useful kind. Could you sum up
the gist of that tool? I'll probably go with a simpler method, but it
just sounds interesting.

And about the MAP sensor... seems like a fun idea, and I've done a bit
of electronics/digital work before so I might revisit it. I think I'll
stick with the oil thing (manometer?) for now.

 

If the vacuum ports you need to hook up to are hooked up to something

I'll probably go with the alternate fuel bottle thing. Seems easier
than propping my gas tank above my carbs somehow. 2 things; First, is
it possible to do the carb tuning with the tank in place, or with the
tank slightly lifted? I can see the screws on the outside of the carb,
3 screws each between a pair of carbs, all pointing towards the rear of
the bike. Second, out of curiosity could I simply put a "T" section in
to drive both my meter and the fuel pump/petcock from the same vacuum?
Would those readings be innaccurate?

Again, I'll probably just use a separate fuel bottle and avoid the
hassle, but I'm curious about alternatives. Thanks for the comments,
they've been helpful (now I just have to find time to actually do it).

 

I'm curious if this would work.

Yes. Make one. USe it. You'll most likely do a better job than your
dealer, even with his $2000 custom analyzer.

Mine is water filled. Stands about 6 feet tall. Hooks onto the rafters in
the garage. Might fill it with fork oil just in case it ever does suck into
the engine. So far, no problem.

I have one of those electronic things. It fluctuates badly at idle. Cannot
remember the name of it offhand as I use the columns now. Starts with
letter "T" I think and takes a forever dead 9 volt battery.

B~

 

I built one and use it occasionally. Rather than just a U, I
suggest a U with a crossover tube and valve at the top of the U.

With the crossover valve wide open, vacuum is equalized between
the two legs of the U. As you gradually close down the crossover
valve, you'll begin to see the fluid lift on one leg and drop
on the other but you should be able to detect this before it
sucks up any fluid.

The valve lets you adjust the sensitivity gradually. If you want
to fiddle with an adjustment, you can open it back up again while
you fiddle then close back down to test it.

Drip irrigation valves work very well for this project. You might
also want to use a carb jet or other flow restrictor in each leg of
the U close to the carb connection.