🚀 go-pugleaf

On the point that one can lift the piston of the HS-4 carb. and check
the effect to determine whether or not the mixture is proper, you're 
right and you're wrong.  

For background in case anyone else cares, the SU, Stromberg, and Zenith
carbs are designed so that the needle is afixed to the end of a damping
piston.  When the throttle plate is open, the inrushing air causes the
piston to rise.  Since it is tapered, this in turn increases the amount
of fuel that mixes with the air.  The piston is dampered with an oil 
cylinder and piston arrangement, so that the changes in air/fuel ratio
are not so erratic.

Now, back to the point.  The test you do implies that you are starting with
the proper needle.  I don't think it will tell you if you have the proper 
needle for the characteristics of your engine.  That is the question that I've
raised.  It really belongs to a more general question: If one changes the 
characteristics of an engine, how do you find the best carburetion for the 
new set-up?  Other stories I've heard lead me to guess that my suspected 
problem of overcarburetion is quite common.

Another point on setting air/fuel mixtures in general: I've found this and
other methods very inexact for setting mixture.  About 6 months ago I bought
a tool called Colortune and have been very pleased with it.  It's really just
a see-thru spark plug with instructions on what color of flame you should be
seeing.  You simply richen out the carb and back up until the flame turns
bunsen blue.  It works fine on both single and multi-carb set-ups.  


					Kurt D. Del Bene
					Bell Labs - WB
					...!ihnp4!homxb!delbene