<VV> Groaning, Backfiring, Loss of Power

[Steven J. Serenska]

VVers:

I am getting some very poor performance lately from my '65 110/4sp 
convertible.  This has been coming on slowly since the summer.  I will 
try to describe all the symptoms, but I'm starting to think that a few 
of them are either unrelated or are red herrings.

This is a long post, but I'm trying to be detailed.  Here goes:

    1) On my annual summer drive up to Maine, at the end of 250-mile 
long trip, the car seemed to be stuttering.  Unfortunately, it was late 
at night and I just wanted to get there, so I wasn't paying as close 
attention as I should have. 

    2) On the same trip, I parked the car for a few hours on a hill at a 
very steep angle (with the nose upwards).  Afterward the car sputtered 
again.   My fear at the time was that when I parked it that way, 
whatever crud was in the tank might have washed back and clogged the 
sock.  The problem disappeared on the long ride home.

    3) Near the end of the summer, I bought a tank of premium from a 
very run down gas station in a bad part of town.  As it turned out, the 
gas must have been pure varnish, because the car ran like a dog for the 
entire tank (i.e., pinging like hell).  It also suffered from a 
fantastic case of run-on every time I shut off the engine.

    4) You might recall that my fuel pump failed shortly thereafter.  As 
it turns out, the cause might have been all the crud in the line and/or 
the tank full of shellac I bought from the gas station.

    5) When I replaced the fuel pump, I took an air compressor and blew 
through the lines back toward the tank.  Everything seemed clear.  I 
knew that I was possibly blowing stuff back to the tank, but mostly I 
wanted to ensure the lines were clear.

    6) This car has an inline filter and I replaced it when replaced the 
fuel pump.  I noted that there was some condensation inside the filter, 
so I also put in a bottle of drygas.  The car ran fine afterward.

    7) About two tankfuls later, the car began severely losing power and 
making an awful groaning noise under acceleration.  The groaning isn't 
to be confused with metal-on-metal grinding, it's just that the normally 
smooth engine seemed like it was groaning under the strain.  About this 
time, the engine also started backfiring like crazy.  The backfiring 
didn't sound much like crud in the lines, so I started to wonder if 
maybe this wasn't a coil problem.

    8) At times, the car would run fine (usually just before I would set 
aside some time to work on it).  One day, however, I pulled out in 
traffic and made a sharp righthand turn.  I lost almost 95% of the 
engine's power and pressed the pedal all the way to the floor.  The 
engine groaned significantly, and then as though a blockage cleared, the 
engine cleared itself and everything was fine.  It almost seemed like 
there was crud in the bowls of the carbs and the sharp turn sloshed 
whatever it was into the line.

    9) Today, the car started out fine and I drove about 30 miles to a 
meeting (on one of the last top-down days in New England).  On the way 
back, I lost 80% of my power again as I was pulling away from a stop 
light.  I was able to get up to speed but I had to keep the pedal to the 
floor just to do 65 on the interstate.  The car was significantly 
backfiring and would barely be able to move under its own power when 
accelerating from a stop light.  It would also stall occasionally at 
stop lights.

So, before I start pulling things apart, does this sound like blocked 
lines, fouled carbs, a bad coil, all three or something else?

I am not a mechanical wizard, so everyone's suggestions concerning 
things to focus on really do help.

Thanks in advance.

Steven J. Serenska

P.S. One other factor that might be coincidental.  This car has always 
had a throwout bearing issue that causes it to squeal now and again.  In 
the past, this would occasionally happen when shifting into first at a 
stop light.  To remedy the problem, I would simply shift back to 
neutral, reengage, and the problem would go away.  Now, however, this 
grinding/squealing noise is happening a) more frequently, and b) also 
when I downshift to second.  I'm not sure this is related to the loss of 
power/backfiring/groaning problem, but I thought I would mention it anyway.