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Carburetor Tuning

To: Spitfires <spitfires@Autox.Team.Net>
Subject: Carburetor Tuning
From: Michael Thomas <mathomas@engmail.uwaterloo.ca>
Date: Tue, 28 Jul 1998 15:22:06 -0400
Hello again!

I have finally got my dual HIF4 carbs installed on the Spitfire and I am
now trying to improve their performance a little bit.  My current
problem is that there is a bit of hesitation on acceleration.  Once the
revs get over about 2500, there is not a problem at all - the engine
sounds very healthy.  There is just the instant when I put my foot down
that the car seems to die out, then the revs (and the car :^)) take off.

Now,  I have adjusted the mixture via the adjusting screw so that it is
as rich as I can get it (it is all the way in).  If I lean out the
mixture (even only slightly) the car will not run well at all -- the car
basically won't accelerate.  Timing is set and is as good as it can get
(I think) and the plugs are good and clean.  Ignition is a Crane
electronic guy...

My first thought was that it was flooding, but that doesn't explain that
I can't lean out the mixture at all without serious lack of power.
There is not a lot of play in the butterfly shaft, and otherwise there
is no obvious air leaks.  One area that I am clearly inept in is the
needles -- I am just using the stock MGB needles that came with the
carbs -- but I don't know if this will _significantly_ impair
performance at low rev/min over such a small range (ie. 1000-2000 rpm).

Any ideas, anyone?

Thanks,

Mike Thomas
'75 Spit that wants to go faster...


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