Before I started trying to balance my carbs using the vacuum guage method I
tried it using a flow based meter. This was a Synchro Test meter (with the
ball floating inside the tube). This meter is the one suggested in the
official Rotax manual and is made in Germany.
I found this method pretty unsatisfactory as you have to hold the Synchro
unit against the carb opening while a rapidly whirling prop is threatening
to chop you up. You have to move from side to side to match up both carbs
with the single meter. This is ok while the engine is idling but pretty
scary at 4000 RPM and needs constant reajustment to keep the ball in the
centre of the column. Im not even sure it would work at high RPM due to the
increased airflow.
As I said before the vacuum guage method (using a matched pair of guages) is
by far the best and easiest method. Once the idle balance was set, running
the engine up to mid range still produced a fairly closely matched vacuum.
It was then only necessary to adjust the cable collar nuts on one of the
carbs very slightly to even up the pressures. In our case this required an
ajustment of two flats (six flats being one complete tuen of the ajusting
nut)
My personal feeling is that the engine is best balanced at about 4000 RPM
which is where the engine runs most of the time. I found that once we had
balanced at this speed (having first set the throttle stops), the engine
idle balance was fairly close and ran smoothly. The trouble is that you dont
realise how roughly your engine might be running until you synchronise the
carbs properly. A badly balanced engine will probably stop running below
1500 RPM whereas when the carbs are set properly you can drop the speed to
as low as 1000 RPM and the engine will still tick over.
If the engine dosen't run smoothly at tickover and you have to increase the
throttle setting to eliminate any rough running then it almost certainly
needs retuning and balancing.
----- Original Message -----
From: "Peter Zutrauen" <peterz@zutrasoft.com>
Subject: Carb Balancing - Flow Balancer?
> I was wondering what is wrong with using a simple flow-based carb
> balancer? Years ago when I was playing with my 'hopped-up' VW beetle
> with dual carbs, this tool worked very well to balance the carbs. Just
> dial the restrictor to center the ball on one carb, then move to the
> other carb and check the ball and adjust accordingly. A few iterations
> and you're done!
>
> Here is the type I am referring to:
> http://www.datsunroadster.com/PIC_PAGES/NEW_PARTS_PIC_PAGES/999-08.htm
>
>
> Opinions?
>
> Thanks,
> Pete
> A239
>
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