We've been working on this section for years:   dealing with the most often asked
questions as people are trying to determine whether or not they need carburetor work.
This page is very general information.  This
link will take you to a page that's just a
little bit more specific
, while this link will take you to an entire discourse on IDLE
issues, starting with the distributor

Please note, I'm told I use too many words when just a few will do. John Jenkins, who
wrote the IDLE section, does too.  
 Have patience and read through this for the MOST
information (probably more than you want along with some redundancy!)

Unfortunately, diagnosing problems, particularly remotely, is like calling your doctor
and saying you have a cough and expecting them to tell you why and what to do about
So many issues that can be caused by a number of different problems.
    Lets start with hesitation. This can be a distributor issue, clogged fuel line, lean
condition, rich condition, spark plug wires or actual plug problem, fuel pump problem,
valve problem, worn butterflies,  or worn carburetor throat, to name just a few.
    So before we diagnose why hesitation, more questions. When do you have
hesitation? Up shift, down shift, starting off, when attempting fast acceleration? Some
other condition?
    Regardless of the problem, check for running rich or lean.
Rich conditions mean cool engine, but it also means dirty tail pipe, popping through
the muffler, dark black sooty spark plugs (one or all - different problems), heavy gas
smell, maybe even gas dripping from carb or down over engine somehow (BAD!!!).
The last two could be bad float, bad needle valve, or too much fuel pressure! check
your fuel pump for proper function, proper pressure.
    Lean conditions are hot engine, light color spark plugs (should be a dry chocolate
brown) -one or all -, popping through carbs (distributor or valve problems will do the
same!). jets clogged? fuel pump working? ALWAYS check the distributor to be sure its
working properly.
    Distributor work is less expensive than carb work. Distributor maintenance is often
overlooked, just like carb maintenance is. And since 6v timing lights can sometimes be
difficult to come by, gets bypassed all together
    We will also ask if your volume control screws are working. some issues involve
them not responding. One not responding, plus only that spark plug being a different
color, are the kind of things that help identify and resolve issues.
  SPARK PLUGS, taken for granted and overlooked.  Recently discussing a rich
running condition in a client's car, realized that I hadn't emphasized spark plugs
enough.  Am not in the position to comment on hot and cold plugs, but can talk about
DIRTY plugs.  While we use plug condition as a diagnostic tool, they go beyond that.  
It is the proper spark, at the proper time, to the proper balance of air/fuel mixture that
makes the engine work.  Distributor controls the time. Carburetors control the air/fuel
mix.  DIRT affects the proper spark.  Pretty much every engine runs rich at idle. Idling
at the stop light is one thing, but are you idling the car to let it warm up? Idling while
waiting for your spouse to come out of the rest room? idling while you are tuning your
carbs? checking your timing?  driving in a parade sloooowwwwllllyyyyy at low rpm's.  
All of these things will load up your plugs.  When your plugs are dirty spark is affected.
If you sit at idle for awhile and then get out there and get your rpm's up, heat up the
engine, that little bit of dirt will burn off.  But for a few moments you may have some
hesitation, some uneven idling.  If that scares you off your drive, you have just left
your plugs dirty and the next time you start up the car, it will be worse.  Poor spark will
not fully ignite the fuel mix in the cylinder and you are left with excess fuel and low
power.  Then you chase your carbs.  
      To check if you are really running rich, start with clean spark plugs, get the car
going and out for a good warm up drive, keeping over 3500rpm.  Plan this out  
carefully because you will want a place where you can just turn off the engine and
coast to a stop.  Then check your plugs.  I
f your plugs are dark, you are running rich.
If they are light, you are running lean.  If you are just right, that nice chocolate brown,
but you have problems transitioning from idle or when running on low RPM's, then a
rich condition at Idle is your problem.

Air leaks? With the engine running, being VERY CAREFUL, spray a little carb cleaner
lightly around the edges of the carbs. If there is a sudden increase in engine revs,
there is an air leak in that area. IF you decide to try this test, stand back.                 
    Matter of fact STAND BACK from your carburetor when ever working on them.
Solex, particularly, spit back with a little flame! Or don't blame me when things get out
of hand and you don't have a fire extinguisher at the ready! Worn butterflies on Solex
mean air leaks, so hesitation because of air flow when the butterflies should be
closed. There might be a ridge worn in the throat of the carburetor if the shaft is loose.
With split shafts, the bracket that keeps the butterflies in sync could be worn causing
them to come out of sync. or maybe the little block has been lost or worn out. Has
your pump rod worn out? the pump cam broken? the pump lever worn out? Is your
check valve still working? On Zenith, is your accelerator pump working? what is the
condition of the pump link? is the shaft twisted? How is your needle valve? Dirty?
Stuck? worn out? Are your floats okay?
    So the bottom line to troubleshooting engine problems (now you know why your
mechanic charges so much) is gathering as much information as possible, and
eliminating all the different possibilities that could be causing the problem. Read your
books. Ask questions on the 356 and 912 forums. Talk to mechanics. Give us a call.
And have as much information as you can, and eliminate the easy ones, one at a time.

You will also find copies of shop manual pages for dual barrel Solex and
Zenith within this web site.
(and I know that is not a Porsche engine!)