No claim that this is your problem, but these are two things that screwed
my SU's all up when I switched to them.
One was the fuel pump. I needed to install an inline pressure regulator
to get the fuel pressure down to an SU acceptable level. Later I learned
that many of the after market mechanical oem type fuel pumps are not
oem in that their pressure is far to high. Don't know the actuall fuel
pressure of my pump, but with an inline regulator stepping the pressure
down to 2 psi I quit pushing gas past the needle valve or Gross jet (I
tried both).
The other was the mounting of the fuel bowl onto the carburetor main
body. An aftermarket kit had been used, with bushings of the wrong
firmness (too soft as I recall), and a bolt of the wrong thread length.
Much to my surprise, a genuine SU rebuild kit has a very specific
thread length that applies a specific pressure to the very specific
bowl mount bushing. The end result is that my bowl was too lose,
resulting in vibration and flapping, with fuel gushing out the vent.
The correct bushing and hardware ended all the motion and
resulting problems.
Once I corrected these two problems, the SUs worked correctly,
and I was able to get them dialed in with good results.
The fuel pressure problem makes me wonder how much of my
ZS problems had been fuel pressure related. I've no plans of
reinstalling it to find out, but I wonder how many ZS woes are
caused by the excessive fuel pressure of aftermarket replacement
fuel pumps.
>>> "Greg Macaulay" <gmacaula@cisco.com> 09/26 7:17 PM >>>
Hi all,
I have a 78 1500 with twin SUs and have just had them converted from
waxstat to normal jets as well as getting it rebushed etc.
The problem is that I can tune the rear carb fine but the front one even
with the jet wound right up will not change engine speed no matter how the
piston is lifted. There is excess petrol and at one point petrol came out
the vent. The floats and valves were changed front to rear with no change
and I have had the front valve seat replaced again. I have not seen petrol
from the vent since I did this but there is still excess petrol.
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