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Balancing carbs with an airline and transmission fluid?

  • Thread starter Thread starter mhobryan
  • Start date Start date
M

mhobryan

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In one of the other forums someone mentioned that they balanced the carbs using an airline and transmission fluid? Anyone else heard of this? How is it done?

Thanks,
Mike
 
Look up "manometer" and "balance motorcycle carburetor" and you'll find dozens of schemes.
 
On a twin, maybe. :-k

On a four, good luck. :p

As themess hinted, there are SEVERAL threads here that have been started by ambitious junior engineers, thinking they could re-invent the wheel. To work properly, there needs to be a certain amount of WEIGHT resisting the pull of engine vacuum. One way to acheive that is with a column of mercury, but that has a bunch of danger involved. Another is to have a much taller column of a lighter fluid, but that gets inconvenient. Yet another way is to use the overwhelming favorite, the Morgan Carbtune. It uses slugs of stainless steel inside calibrated tubes. I have not checked today's exchange rate (it comes from the UK), but it runs about $110.

Many of the junior engineers are of the opinion that you can balance the two carbs on one side, then balance the two on the other side, then finally balance the two pairs to each other. My experience has shown that it never works that way. Any change to any adjuster tends to affect all the carbs, and there is no way to see that unless you have a gauge that will view all four at the same time.

.
 
What Steve said

Sure, you can do it for $25 (or whatever), but then you endlessly mess with the thing to get it to work correctly

If your time is worth nothing, go for it

And, don't buy those cheap dial gauge sets off Ebay. You'l be endlessly recalibtrating them

By the time you're done getting them ready to sync your carbs, your Morgan will be back on the shelf and you'll be out riding
 
Carb tune is a great investment. Bought mine in 06 and Ive used it on countless bikes. Unless you drop it or something else of the wall happen it will last you a life time.
 
I've seen internet instructions for two home-made manometers that will probably work.





Instructions on how to make and use each of them will run to roughly two full pages, single spaced. I can post them if anyone is interested, but I've never tried either one. Construction and use are literally science projects. They are not likely to work unless you understand how they work. OTOH, to use a Carbtune, follow the instructions.

One device not mentioned yet is a tool to tighten a lock screw while not moving the adjustment screw. Those seem essential, regardless of the method used to measure vacuum. The tool is available where ever Carbtunes are sold.
 
I've used both the vacuum gauges and the Motion Pro Syncpro with good success on individual throttle bodied cars. I found the gauges were a bit finicky and subject to pulsing more so than the liquid filled tool. That being said I have yet to use them on an actual bike. ;)
 
I too was looking for a cheap alternative earlier this year without much success. Everything just looked cheasy and my time IS worth something to me. I finally saved up the money and bought the Morgan Carbtune (and the tool to turn the adjusters) and couldn't be happier. I had my 4 carbs synced in 10 minutes. Worth every penny.
 
The blue bottle one looks good to me. I've used a similar one on a twin. Here's a link to recent discussion here on the forum
http://www.thegsresources.com/_forum/showpost.php?p=1937870&postcount=11
...the bottlething works by levels in the bottles changing where one vacuum is stronger.
It's pretty easy to see when vacuum is equal when you are doing it.The levels stop changing. I suppose there are subtleties beyond that, the "mass" of the oil medium, pipe wall friction, inertia,properties of air as a gas, that fudge a perfect synch but these apply in other Manometer designs too. Anyways, on first hooking it up, it's pretty obvious when they are out of synch. After that, it doesn't take much of a screw-turn to make things happen after you slow the "obvious" transfer of fluid down.
The slower the fluid transfer, the better is the synch.
It occurs to me that you could do a four-cylinder bike with just a two bottle setup.

I've never seen it "pulse" -there's enough air to act as a shock absorber.
I tried an old fashioned dial vacuum guage first but it pulsed so much it was hopeless, though a friend of mine used it on a twin and said "Good Enough" just watching the peaks of the needle. He may be right, given that the overall precision of the Universe is an illusion.
 
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Ghost..if you dampen them till the needle JUST stops twitching they are set..and I lay them on a folded up towel so vibration doesnt make them react.
 
so Viscosity is a good point.... Kerosene or diesel or water should be useable. ATF has a nice visibility though.
 
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