88 Accord "Sputtering" Problem

You guys helped me with my idle issue but now I have another problem.
I have an 88 accord, carburated, with roughly 180,000 miles on it.
Going down the freeway the other day I noticed that when I get to
around 65-70 mph or so, the engine starts to sputter. It only does it
when I start going past 60, not when I'm just traveling in the city. I
have given it a recent tune up, with cap and rotor, spark plugs and
wires, both fuel filters, a new PCV valve, air cleaner. I just don't
know what else it sould be. This car is never ending. I've heard that
it might be the catalytic converter. If you could give any suggestions
that would be great!

Thanx

 

Maybe a carb float adjustment or a vacuum advance leak?

 

The central question is one I got from the punchline of a joke I heard 30
years ago: "How does it know?" (In the joke it referred to the ability of a
thermos to keep coffee hot and milk cold.)

What is it about the freeway speed that it cares about? Maybe the RPM or the
fuel flow, or the overall power demand or perhaps something is getting hot
from the power produced. A few simple tests will narrow that down. RPM is
easy, by seeing how it performs at freeway rpms in lower gears. RPM trouble
usually means the ignition, particularly the distributor. Take the
distributor cap off and look for signs of rusty powder around the shaft.
That is a common sign of trouble, but absence of rust is not a clean bill of
health. Fuel flow is harder, but try this: take the car up to the upper end
of the range (whatever you can safely and legally do on the freeway) so it
is sputtering, and back off on the throttle so it drifts down about 5 mph
without producing much power in order to allow the float bowl to fill if it
is low. Then level off the speed - still in the "sputter" range - and see
how it behaves. If it runs smoothly a few seconds and then starts sputtering
it is likely the fuel delivery is not what it should be. If both tests are
negative - doesn't behave like rpm or fuel flow - I would tend to suspect
the coil is getting hot and breaking down... but you would probably want to
check deeper before springing for a new coil, even from a wrecking yard.

It could be the catalytic converter but that isn't my first thought. If you
have a plugged cat you will also notice the last half or so of the throttle
only seems to make acceleration worse. There are other tests but try the
ones I mentioned first.

Mike