[T3] Chasing Engine Gremlin - Popping

[Robert Bills]

As some of you know, I recently put a '73 Squareback back in service after 14 years of storage by the original owner. Stock fuel injection.
.
The engine starts almost instantly when the starter in engaged.  Idle is very rough when cold, but evens out a bit after several minutes at a high idle.  Depending upon how many days the car has been sitting, there is sometimes a puff of of smoke at cold startup and the exhaust smells rich.  My practice has become to warm up the car at least 5 minutes before backing out of my driveway.   (I'm in SoCal).  Valves are adjusted; new plugs; dwell and timing are set to specs.  All factory fuel, injection and hoses are intact.  No vacuum leaks.  All wiring connections and grounds have been checked. Fuel pressure is a constant 29 psi. Compression tested 135, 135, 130, 135.  All cooling tin is in place.


Approximately 500 miles ago, I had my work checked by a highly recommended local VW mechanic who knows the D-Jet fuel injection system well enough to think that converting to carbs is an admission of failure.  He gave the engine a clean bill of health, but observed that he felt a "slight flat spot in the midrange" that he suspected could be related to an injector.  [Not surprising after 14 years of nonuse].  He suggested that I drive the car awhile to see if the problem cleared up on its own, stayed the same, or became worse.


During the last several days, the "flat spot," (slight hesitation after shifting into 2nd), which had been very minor and easily masked by more agressive acceleration, has degenerated into a "popping" when I try to accelerate in 2nd.   This seems to be related to the engine operating temperature because it happens most during the first 5-10 minutes of driving (after the 5 or so minutes of warmup in the driveway), even on warm days.  This occurs whether it is the first start of the day, or a start after sitting several hours in a parking lot following a cool down from a 20 minute freeway drive.   The popping almost never occurs after engine is clearly warm (although the "slight hesitation" is still there).


The popping concerns me, but I don't have a clue where to start or where to go from there.  What do these symptoms suggest?  Are these engines really that cold blooded?
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.vwtype3.org/private.cgi/type3-vwtype3.org/attachments/20110331/4d0707fe/attachment.htm>