I agree with Larry (MKIX) about adjusting the SU’s…only would like to
add…the rubber hose bit is ok, if you have the ears of a B-17 pilot and
can “sync” the carbs that way… Simple solution (Note: NOT AN AD!) get a
“Unisyn” tool, it allows consistant adjusting of the air flow on multiple
carbs–side or down draft…makes life easy.
Charles #677556
FWIW - two points from my experience with SUs:
The use of a Unisyn is somewhat controversial because the instrument has
to restrict the flow through the carburetter throat and thus changes
what you are trying to measure (the hose has an insignificant effect).
I think with proper adjustment, the engine will speed up momentarily and
then slow down and run evenly on the three cylinders fed by the working
carburetter (the mixture should not be rich enough to keep the other
three running through the crossover tube).–
Bruce Cunningham’s web site: http://www.together.net/~bcunning/
“The proudest nettle grows on a midden (dung heap).” (Scottish proverb)
I agree with Bruce about the Unisyn “restricting” the air flow.
Having used a Unisyn for a little over thirty years, I have found if one
“opens” the restrictor in the venturi the air flow is not reduced to affect
the running of the engine.(I have a Snap-On HC/CO2 gas analyzer that shows
the percent of “fuel/air” mixture, I use this in conjunction with the Unisys
when setting carbs.) One must then “close down” the restrictor just enough
to get the little red “ball” to rise up the tube on the side of the unit.
This will then allow equal air flow to be set between carbs.
I have used this sucessfully on twin and triple SU’s, twin
Nissan"SU’s" and quad Honda 750cc motorcycle carbs.
Like any tool, ya gotta know how to use it.
After setting the “air” with the Unisyn, set the mixture, re-check
the “air” then use the little button under the dashpots the verify the
settings are correct.
My father could set twin SU’s on a Volvo with a tube, but he was a
B-17, B-29 and other multi-engine rated pilot and could “sync” the engines,
from the cockpit. by ear. He had over 5000 hours in the air. I never
developed that talent. I have to use a tool.
Charles #677556-----Original Message-----
From: Bruce Cunningham bcunning@together.net
To: xk@jag-lovers.org xk@jag-lovers.org
Date: Friday, June 18, 1999 1:45 PM
Subject: Re: [xk] RE: S.U. Question
FWIW - two points from my experience with SUs:
The use of a Unisyn is somewhat controversial because the instrument has
to restrict the flow through the carburetter throat and thus changes
what you are trying to measure (the hose has an insignificant effect).I think with proper adjustment, the engine will speed up momentarily and
then slow down and run evenly on the three cylinders fed by the working
carburetter (the mixture should not be rich enough to keep the other
three running through the crossover tube).Bruce Cunningham’s web site: http://www.together.net/~bcunning/
“The proudest nettle grows on a midden (dung heap).” (Scottish proverb)