I'm with Jim on this one. Having the tach reading change simultaneously
with a power problem indicates that it's likely an ignition issue. The
amount of voltage required to ignite a mixture is proportional to the
cylinder pressure, which is why a bad coil will sometimes allow the car
to idle but not be run at a higher power level. As Jim suggested, check
all your electrical connections between the fusebox and the coil, and
then swap out the coil and go for a test drive. So far as it leaving you
stuck by the side of the road - it's already doing that, so swapping the
coil with a known good one can only improve things.
On the fuel side, I've also had the exact problem described where crud
in the filter would get sucked up around the element over a few minutes'
driving and kill the engine. Waiting five or ten minutes would let the
junk settle to the bottom of the filter can again, and the car would
fire right up and run perfect... For a couple of minutes. Put on a clear
filter just ahead of the carb and see if anything collects in it.
Good luck,
Theo
|