Anything you stick in the front of a carburetor screws up airflow into that
carburetor. That's how it gets a reading in fact. If you were to place an
identical snail in front of each carburetor at the same time, that would work.
It would screw up the air flow uniformly. But doing it one at a time creates
imbalances across the carburetors, producing false readings and therefore
isn't as accurate. There's also the matter of the inherent accuracy and
stability of the tool itself.
As for how critical is synchronization and where do I come down on it, that
varies a bit. With these engines, the multiple cylinders per carburetor, and
their very large balance tubes, you can be pretty sloppy and have things
running quite well. With dedicated carburetors and runners to each cylinder,
like on a motorcycle or multiple DCOE's, it doesn't take much imbalance to
have an engine that surges and splutters under light load. Personally, I'll
balance as accurately as I can with the equipment I'm using. It only takes
about half a second to go from "pretty close" to "dead on" with a synch
stick.
Remember too that synchronization is irrelevant from about 1/4 throttle up.
The values are too gross. It's at those close throttle positions that it
matters. The closer the throttle positions are to closed, the more it matters
and the more sensitive things are to changes. Floored at 5000 rpm, there's no
such thing as synchronization of the carburetors. But coast down a hill at 40
mph with just a little throttle to maintain speed, and lack of synchronization
gives you a lurching vehicle.
And Randall, I said throttle blade, not piston. There is a difference you
know. Most carburetors have a specific throttle blade clearance listed for
initial installation. This value is also usually included in the
documentation that comes with a rebuild kit. While it sounds super accurate,
in reality it doesn't work that way for many reasons.
And a manometer is not a synch stick. You need multiple manometers to make a
synch stick. The name synch stick is old and well known to those in the
field. As the mercury units were replaced with multiple gauge banks like I
linked to, the name carried over to them as well. My bank of gauges is
frequently called a synch stick by the mechanics in the motorcycle shops.
----- Original Message -----
From: DLylis@aol.com
To: foxtrapper@ispwest.com ; triumphs@autox.team.net
Sent: Wednesday, December 06, 2006 7:54 AM
Subject: Re: [TR] Carburetor Synchronization tool
Why is this different than the "snail"? Although the snail does not
"measure" vacuum it does measure the vacuum relative to each carb. I
understand that the carbs need to be synchronized, but which side of the "it's
not all that critical" argument do you come down on?
=== This list supported in part by The Vintage Triumph Register
=== http://www.vtr.org
|