Lotus Elan

Manometers was: timing problem

PostPost by: "Roger Sieling" » Wed Apr 27, 2005 1:11 pm


You just never learned the proper way of "listening to carbs". It is very repeatable if you put the listening tube into the same spot each carb throatevery time. I have been doing it for over 30 years this way with all the perfection I can stand, on both street cars and race cars. It just takes a bit of practice, or maybe someone to hold your hand the first time. I totally agree with your accessment of Unisyn tool, and although I have one, I've maybe used it only once or twice in 30+ years.


>> ***@***.*** 4/26/05 7:27:26 PM >>>

Hi Tom. I saw your response below and was a bit surprised.

I think I've tried most methods at carb synchronizing over the years
so my preference of methods, in decending order, from least effective
to most effective, is as follows:

1. listening to the air hiss using a tube to the ear - not easily
repeatable and very subjective

2. a Unisynch - affects engine running at idle and is sensitive to
orientation. Can only look at one carb throat at a time

3. a BK synchrometer - gives a measure of flow rate but only does
one throat at a time. By the time you cycle through several carb
throats, the engine rpm has changed or you forgot the previous
reading. The best way to use a Synchrometer is to fix one in a carb
throat and use a second one to match the remaining throats to the
control meter. This method requires matched Synchrometers.

4. a 4-tube manometer system, one per throat, measuring the manifold
vacuum of all carbs simultaneously - all throats are monitored
constantly. An adjustment to one will affect all others and this will
be immediately visible and measureable. Actual readings are not
important, only that all columns are the same height.

Prior to purchasing a pair of 4-tube manometers for my F-car, I
considered the carbtune-II, which uses metal rods floating in a
tapered bore of glass. Environmentally, this is a good way to go but
I wasn't convinced the performance/accuracy was there.
Irregularities in the tapered bore, bore verticality, or a
contaminant causing intermittant sticking of the steel slug, was a
potential problem. In the end, I thought it difficult to beat
mercury, with all its toxicity issues. There is no sticking of the
fluid or dependance on bore taper or verticality.
Sensitivity/pulsations can be be controlled by line restrictionsl
It's the the verticle height of the column that counts. When the
columns are equal, the manifold vacuums are equal, the flows are
equal, and the engine will tick over nicely if the mixtures are

Balancing carbs is really an issue at idle and off idle. A good
balance allows one to accelerate smoothly from a stand still with
smoothness and little effort. Low speed gear changes are much
cleaner. Fuel economy is improved. I'm a happy driver.

The down side is that one has to install vacuum taps in the intake
runners. At idle, air flow is very low. Position of the tap is not
real important IMHO but, I would/did position the drilling/tap
fitting a reasonable distance from the butterfly valve of the carb.
In the case of the Weber TC head of my S2 Elan, I hid them on the
underside of the runners. For my F-Car, I modified the air injection
(emissions) plumbing from steel tubes to flexible (silicone) tubing
and achieved the same result. Balancing 8-throats is more difficult
than balancing 4-throats, but manometers make it predictable and
sure. Once you've tried it, you'll kick yourself for not always doing
it this way. The results are quite obvious to the tuner.


--- In ***@***.***, "tom moore" <[email protected]>
More manometer tales. I can't believe anyone would actually do this!

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