Hi List,
Well, after many months of not having time or heated garage to tinker with
the Spit, I finally got out there this past week as the weather warmed up.
After a short battery charge, it fired right up and ran pretty smoothly once
things started to warm up. A friend recommended that I hook up a vacuum
line from intake manifold (I have dual SU HS-4s on a rebuilt 1500 engine -
dual valve springs, Kent cam, 9:1 pistons, Kirk Racing header, etc.) to the
older, points operated distributor on loan from Clark Nicholls (many more
thanks, Clark!).
I had driven the car w/out the vacuum line and it ran poorly. With the
vacuum line hooked up, it seemed to run much better, but it's been so long
since I'd driven it, I wasn't sure if it really was better. Or, to put it
another way, were the things I perceived as possible "problems" during this
drive really problems or have I just been spoiled by driving a brand new
Miata and various (forgive me) 308s? It seemed to run with more power, and
fairly smoothly. At one point, running up through 1st there was no
hesitation or stumble or loss of power. At another point (again in 1st), it
still seemed to have the choking, coughing, wheezing loss of power I had
experienced previously.
When I first installed the SUs, I was getting fuel out the overflow/vent
pipes despite having gross-jets installed. So I put a pressure regulator in
the fuel feed line. This led to other *interesting* things. Specifically,
at high revs, the fuel seemed to stream out of the overflow with the
regulator set to 1 or 2psi. When cranked up to 5psi, the overflow stopped,
even at high revs.
So here's the real questions:
1. What should the fuel delivery pressure be for SU HS-4s w/ mechanical
fuel pump?
2. Anyone know the output pressure of a stock mechanical fuel pump?
3. Why would the gross-jets not be shutting off fuel flow? Even with as
little as 2-3psi, it seems that the plastic float and ball-bearing style
gross-jets wouldn't be enough to shut off fuel flow. Thoughts?
4. Why would the overflow situation disappear when the pressure was
*increased*?
5. Given that the gross-jets *should* be shutting off fuel flow, but
aren't, what would be the benefits/risks of installing a return line from
the float-bowl overflow/vent pipes to the inlet side of the fuel pump?
Assume that a check valve would be installed right before the "T" going back
into the inlet side of the pump to prevent fuel from going the "wrong way"
in the overflow tube.
Thanks a lot for any help/answers any of you can provide.
George Parker
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