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Re: [T3] please (trouble)shoot me!

<x-charset iso-8859-1>> Y'know, it's always something.
> My car is running poorly.  Doesn't want to hold idle, bucks and pops at
> RPM ranges, painfully slow.

Check the fuel pressure to make sure it isn't running lean (possibly the
reason it's backfiring through the intake).  This could also cause bucking
or surging.  It sounds like there may be a problem in the idle circuit of
your fuel system, or there your carbs may not be accelerating at the same
rate. (you do have carbs right? if not maybe one of the other FI specialists
in the group can help).

> Fiddling with idle, mixture, advance, retard produces no desireable
> Valves, gap, dwell all within spec.  Plugs firing correctly.
> Compression on #2,3,4 all bteween 100-105. #1 down around 90lb....
> #1 plug is a little dark, but NOT completely fouled.  No blue smoke, so
> pretty much eliminates pistons, rings, cylinder walls - right?

Your compression isn't too far off (10# is acceptable) in number 1, but to
be sure have you run a wet compression test as well?  To determine if the
problem is in the cylinders or in the heads, squirt some oil down the
cylinders and re-record the results.  Remember to make sure all the plugs
are out in all four cylinders before running the compression test, and turn
the engine over at least 3 or 4 revolutions per cylinder - otherwise your
readings may be inaccurate.
If a wet test doesn't make a substantial difference in the compression,
there could be a head problem, but don't just assume so.

> Fire - yes, actual bursts of flame - occasionally issuing from both
> pipe and carburetor.  Which means it ain't just one stuck lifter,
> lobe, or mangled  pushrod, right?

If you can isolate one problem at a time, you may find several smaller
problems causing multiple symptoms.  Usually you won't get misfiring through
both the intake and the exhuast unless multiple problems are present.
Perform a power-balance test to see if #1 makes any noticeable change in the
RPMs. :

Power-Balance Test
This test provides a good indication of how much each cylinder contributes
to the overall power output of the engine. In addition, it also isolates
which cylinders contribute little to manifold vacuum.

You can perform a power-balance test at home on any air-cooled engine except
those with electronic ignition.

To perform a power-balance test,

  a.. Remove all the spark plug leads from the spark plugs.
  b.. Set the leads lightly back on the tops of the spark plugs.
  c.. This will enable the lifting of each lead off its plug without using
too much force.
  d.. The procedure is to pull the lead away from the plug and ground the
lead against the cylinder head. This will prevent that plug from firing -
this is called open-firing.
  e.. The engine will now be running on only three cylinders.
  f.. By comparing how the rpm drops for each cylinder as it is disabled
  g.. If a cylinder is faulty, then as it is disabled it will have little if
no effect on the engines rpm, as it will not be contributing fully to the
overall engine power.
  h.. If there is a suspected burned valve or other major problem, a quick,
ear-calibrated power- balance test will indicate which cylinder it is.
  i.. Because VWs have only four cylinders, a faulty one will show up
relatively quickly.
However, if you are looking for a more subtle problem, use a Tach Dwell
Meter or Tachometer to measure the exact rpm drop for each cylinder.

> So, what are my best & worst-case scenarios here? What have I overlooked?
> What else to check before I assume a cracked head, pull it and get new?

Exhaust as many possible tests on the engine in the car before you pull the
engine and/or a head.  Otherwise, it will be more difficult to isolate the

68 Notch (Nadine)

I proudly buy my aircooled parts and service from...
The Bug Stop in Arlington (DFW), Texas

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