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Homemade Carb Sync

  • Thread starter Thread starter hwb120240
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hwb120240

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Somewhere in the last month I saw a homemade sync that used PVC pipe with end caps as a plenum, a 4 valve aquarium bank, and a vacuum guage. I downloaded the info and picture but that computer crashed and I lost the info! Does anyone remember this? If so, I'd really appreciate it if it was re-posted or even if you'd just email me at: hwb120240 @ bellsouth.net

Thank you,
Wayne

BTW: What range does a vacuum guage need to have to be useable in carb sync?
 
I made a sync tool like discribed in the link using two vacuum gauges with a range up to 30 inHg - bike pulled about 10 - 15 inHg while running (as I recall). Even with the plentum, the needles fluctuated quite a bit. Adding a restrictor into the feed lines is recommended. At the end of the day the whole project cost more money that I estimated; PVC pipe, PVC end caps, brass fittings - plus with a GS Suzuki you are going to have to come up with some sort of threaded attachment fittings to get into the carb boots (not cheap unless you make them yourself).

As a side note, I wound up purchasing a mercury sync tool last month for $50 which ultimately would have saved a whole lot of messing around. The threaded adaptor fittings would have cost about $17 shipped and I couldn't see spending any more money on the whole mess only to have a twin gauge system.
 
Thanks Folks

Thanks Folks

That is what I was looking for, thank you,
Wayne
 
My carb sync manometer consists of about 15 feet of semi-transparent (ie so I can see the water inside) small diameter tubing, about a 5 foot long board, some coax cable staples, a couple of automotive vacuum tubing restrictors (basically, a really small hole), various sizes of vacuum tubing hose connectors, and water.

Staple the tubing to a board in a U shape. Put some water in it. The restrictors act as dampers so the water lever changes more slowly. The silicone tubing can't be used near the engine because the tubing gets too soft from the heat. But a couple of chunks of vacuum tubing connected to the silicone tubing in an air tight manner solves that problem. Stick the tubing on the carbs (obviously, you can only do two at a time) and start the bike. Watch the water level in each leg of the "U" and adjust the carbs until they are equal. Works great.

The water in the tubing is way more precise then any mercury based manometer can hope to be. And if you suck water into the engine: no harm done.

Tips:
-Of course the two carbs not being synced need to be capped off.
-Luckily, all carbs are synced relative to number 2 on GS's (and Honda CB900's). That makes things much easier. Start by syncing 1 to 2. Then 2 to 3. Last, 2 to 4. Must be done in that order because the adjuster on 4 is connected to 3 so any changes to 3 also changes 4.

The only down side is that you can only do 2 carbs at a time and you have to move more hoses and caps around.

Cheers
 
Hey Brian how about a diagram for those of us that cant quite visualise your description.

Rehards

Don
 
is it possible to just hook a vacuum gauge to each carb and adjust them that way? if you had 4 vacuum gauges would this work?
 
80GS750 said:
is it possible to just hook a vacuum gauge to each carb and adjust them that way? if you had 4 vacuum gauges would this work?
Click to expand...

Yes, of course. Try to hook each one up to the same cylinder first to gauge calibration. Also, the factory sync tools have a restricter in the vacuum lines to damp needle osculations. Much needed.
 
I've seen this technique on some BMW forums also, but I never bookmarked the links. The BMW guys with twin cylinder boxers like it because it works so well with only two carbs. I did bookmark one page with a nice picture however. Mine homebrew setup looks very similar to this guy's:

http://www.rightspin.com/motorcycles/LowCostMano/mano.html

Only differences are
-This guy uses transmission fluid which is silly. Water is fine and is actually more precise. It takes less pressure to move the column of water. In other words, the difference between the level in each leg would be greater with water given the same pressure difference. Either way, it gives you way more precision then necessary. It is kind of like using a micrometer to measure a wooden board that you are going to cut with a hand saw. Not quite that extreme, but you get the idea. Precision overkill.

-This guy is also very concerned about making sure the loop makes a perfect semi-circle at the bottom of the "U". This is unnecessary (although it does count on the neatness scale). The tubing can be draped across the floor and it would still work the same. Carpenters use the same setup to, for example, make sure a house foundation is level. Run a hose filled with water across the ground from one edge of the foundation to another. The atmosphere is pushing down on the columns of water in each leg the same amount. If you ran a string from on end of the hose to the other matching the string up with the top of the columns of water (imagine separating the two legs of red liquid in the picture some distance apart), the string would be level. (Well, technically it's not. Gravity is still pulling down on the string causing it to be a parabola. But, for all practical purposes and as far as a human can tell, it is strait and level.)

Other cool tips:
-A restrictor is important. Otherwise the pulses of the engine will cause the columns of water to move up and down too fast to get an accurate measurement. Go look at the vacuum tubing isle of any auto parts store. A restrictor is simply a very small hole through a tubing connector.

-It's fun to blow/suck on the tube and watch the water move.

-To make sure there are no leaks, simply use a"Y" connector (again, vacuum tubing isle of parts store) and hook up to one intake manifold (or just blow in it). No water movement means no leaks.

-Remember, we only need to measure relative differences between carbs. Thankfully, carb number 2 is pre-set and non-adjustable so we don't have to worry about a starting point or measuring any real pressure value. It is the "tuning fork". The other carbs just have to match up to that one.

Latter
 
wouldnt it be cheaper to buy 4 vacuum gauges and some restrictors then? why play with all the fluids and such?
 
The only fluid is a few mL of water. You only load it into the tubing once, and then you hang it on the wall.

4 vacuum gauges cheaper then a few feet of tubing and some connectors? Those would be some pretty cheap gauges.

You can buy 4 vacuum gauges if you want. In fact some of the commercial sync tools are just that. Four different gauges necessitates well calibrated, accurate gauges. Perhaps it would be better to buy one gauge with high precision, and measure and adjust each cylinder one at a time. But again, an inexpensive set may work just fine. I've never tried any, but I have seen mixed opinions on other forums.

Don't get me wrong. I am still a tool nut. If someone gave me a nice set of vacuum gauges or a 6 cylinder mercury manometer, I wouldn't turn them down (well, perhaps I wouldn't want the mercury.) But my water manometer is simple, elegant (think of it as a water sea-saw), and dirt cheap (granted, I had most of the parts already on hand). It also has a high geek index value. But hey, use whatever works best for you.

By the way, you use the same basic technique with a Twin Max:

http://www.ascycles.com/detail.aspx?ID=2146


Later
 
Last post, I promise...

Ok fellers, just so y'all don't think I'm crazy...No one does it quite like the Germans:

http://www.gs-classic.de/index1e.htm

(Rough) English translation site:

http://babelfish.altavista.com/babelfish/tr

This is the German equivalent of our site. I didn't do any searching to see if it is referenced somewhere else on thegsresources.com. Anyway, if you click on the "Tipps" tab at the top, then on "Carburetors Syncronize" and finally on the "here the building guidance" link in the 1st paragraph of the article...ta-da--a four column home-brew oil manometer. And if you go to the bottom of the page, there is a short paragraph describing the two column manometer made out of a chunk of tubing just like I use. That one uses oil. I still say water works fine.

Again, use what works for you.

Awesome German site, buy the way. But hey, this one is pretty awesome too.
 
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