How vexing! One thing we've had happen is for some debris to be in
the bottom of the float bowl and either restrict fuel or
intermittently shut off fuel to the carb in question. With the SU we
had a little flap of rubber in the connection between the float bowl
and the carb body that was a PAIN to find, but with the ZS it's all
one piece. I think it's pretty easy to remove and clean out the
needle valve in the carb while you're at it.
We had a fuel delivery problem (in a race car) that was caused by a
pressure regulator - it would lay down at the end of the straight but
backing off the gas would tend to make it run better. Kinda sounds
like the same symptom you're fighting. A long time under high
throttle opening in a tall gear using more gas than the system could
supply for some reason.
I think you mentioned this but stock fuel pump? Might try
temporarily putting a low pressure electric one in the line to see if
somehow something with the pumping side of things is an
issue. Something restricting fuel flow SOUNDS like a strong
possibility - the question is WHAT, of course.
- Tony
At 03:23 PM 9/18/2010, Dean Mericas wrote:
>Original message:
><Symptoms:
>- Car runs well and with full power for a while after start-up.
>- Loss of power and what feels like a miss under load after it's been driven
>a while. Going up a long hill seems to trigger the stumbling. If I let up
>on the throttle, it smoothes out. Sometimes it drives well again for a
>while.
>- Problem seems to be worse when it's really hot out (I live in Austin),
>although it also happens on cool mornings
>- Engine idles smoothly even when it's not running well under load.>>
>
>You guys have been great in coming up with ideas. This is what I've done so
>far (without any apparent effect on the problem):
>
>- Swapped out the coil with a good used Bosch unit
>- Swapped out the Pertronix ignitor unit with a set of points, gapped them
>to spec, and set the timing.
>- Checked the advance mechanism, and it does.
>- Checked the spark plug gaps
>- Checked the oil level in the carb dampers (ZS carbs)
>
>Other suggestions that don't seem likely:
>
>- Water in the gas. The fuel pump bowl is absolutely clean w/no trace of
>either water or debris.
>
>- Hung up fuel valve in one of the carbs. It seems like gravity would tend
>towards a failure mode with too much gas not too little. I'll probably
>check this if all else fails.
>
>- Kink in one of the soft gas lines. I looked at the various sections and
>they all appear OK, at least superficially. I may go ahead and replace them
>all if I end up draining the fuel system.
>
>I'm open to other suggestions. Is there any chance that some valve train
>issue, such as a weak or broken spring, or a burned valve could be causing
>these symptoms? It seems unlikely since the problem is intermittent.
>
>I'm thinking that he next step is to drain the fuel tank and back blow the
>fuel line to convince myself that there is nothing clogging it. I'm running
>out of ideas if that doesn't solve the problem. This car has been
>remarkably simple to maintain and reliable in the 19 years that I've had it.
>This loss of power at high speed problem is getting pretty frustrating.
>
>Dean Mericas
>Austin, TX
>1965 TR4 / 1974 2000 GTV / 1976 Giulia Nuova Super
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