I have a question for the SU experts on the list. My '67 Midget vintage
racer (twin 1 1/4" stock carbs) has always "stumbled" upon exiting tight
turns. I've checked all the other systems and have pretty much determined
it is probably a fuel delivery problem. Fuel pressure is OK at 3 psi. My
latest
theory is that the floats are oriented incorrectly. The stock set up is
such that the float chamber lids have the inlet pipes facing where the fuel
lines can get to them easily. In addition, the rear carb is fed from the
front carb, so the front lid has both an inlet and an outlet pipe while the
rear lid has an inlet pipe only. The float hinge pins therefore are
oriented on my race car as well as on my street car ('72) and all my parts
cars at a 45
degree angle to the centerline of the car. This is what I think attributes
to the starving problem. The G forces, or the sloshing fuel raises the
float, closing the valve, and starving the engine of fuel after it sucks
the fuel out of the chamber. A few hundred feet down the track, I'm back in
business because the the car has leveled out, the float has dropped, and
the chamber has re-filled. Surreptitious inspection of numerous SU equipped
cars at the last race resulted in about half with this orientation and the
other half with the lids turned such that the float hinges are
perpendicular to the centerline of the car. You can tell this from the
outside of the lid by the direction of the "bump" that houses the hinge
mechanism. I use a fuel block that feeds the carbs independently of
eachother, so I don't have to consider the front feeding the rear.
My question is this. I've been having a hard time finding lids from my
spares that are oriented the correct way and don't have the pipes facing
the dashpot or the K&N filters. Since I have the fuel block feeding
each carb separately, each of the carbs needs an inlet only and not an
inlet and outlet to the other carb. Can I use a rear lid (inlet only) on
both carbs. Some of the race cars I looked at had the ears of the lids cut
off and the lid rotated on the fuel chamber until the correct orientation was
obtained. The lid is then held to the chamber with larger washers under the
screws. I don't like this arrangement very much because the lids don't seem
to me to be screwed down reliably enough considering the vibration under
the hood.
I also realize the little hole in the lid under the inlet pipe is an
overflow vent and must be kept clear. But it sits right over the hot
header! Has anybody seen fit to insert a small brass tube and vent it to a
safer place? Or is the little metal deflector sufficient?
Does anybody have any recommendations or experience in this area? Although
my solution seems logical to me, are there any problems with it? I
certainly am open to any input from anybody with a better solution. And,
no, I won't go to a Weber!
Bob
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