Carburetor jets: determining factors

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2 total messages Started by Bill Pataky Thu, 17 Oct 1985 14:32

#25

Author: Bill Pataky
Date: Thu, 17 Oct 1985 14:32

25 lines
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    Can someone explain to me what factors are involved in selecting the
correct carburetor jets for a particular configuration of a particular engine?
I own an '80 Spitfire (USA market) with a 32/36 Weber Carb.  There are no
emission controls on this engine, and between the addition of the weber and
the removal of the Emission controls I have significantly improved the engine's
power output over the original 53 (whopping) hp.  The car was also marketed in
Europe with the same engine with no emissions devices and a different cylinder
head giving it significantly more hp with a 9.5:1 comression ratio versus the
USA market's 7.5:1 compression ratio.  I have the oppurtunity to have a friend
in Europe buy a European cylinder head and bring it over.  My question arises:
should I re-jet the carb when I get the new head?
    After thinking about it, I came up with 2 factors that determine jetting.
One would be the expected operating speed of the engine, and the other would be
the displacement of the engine.  Since I am not changing any of these, I would
assume that I would not have to re-jet the carb. Am I correct?
 
        Thanks...
 
        Bill Pataky
 
        Parallel Processing Lab
        University Of Maryland
 
        pataky@gymble.umd.edu

Re: Carburetor jets: determining factors

#30

Author: Kevin Szabo
Date: Fri, 18 Oct 1985 15:38

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You have left out a number of factors... one of which is the cooling
effect of the gasoline.  By running rich the air/fuel mixture is cooled
and stays dense.  Hence the total amount of air/fuel that is introduced
to the combustion chamber will be greater and more power will be generated.
Too much fuel and you start washing the oil off the cylinder walls.
I suggest you pick up a short book on carburation from your local library
or bookstore.  Most of the major factors will be discussed.

	Kevin

-- 
Kevin Szabo' watmath!watvlsi!ksbszabo (U of W VLSI Group, Waterloo, Ont, Canada)

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