🚀 go-pugleaf

I have a 1970 Porsche 914-6 with a peculiar hesitation problem.  The car
runs fine if I 'take it out for a drive'.  However, if I try to use the
car again after a period of 15 minutes to 1 hour, it starts and idles fine
but the first time that I go for higher (> 3500) rpm under load conditions 
(as opposed to just revving the motor) it hesitates and bucks.  After several
blocks (sometimes up to a mile) it will be back to normal again.  It seems
to be independent of outside temperature or the distance which I drive, as long
as it's more than a mile or two.  A recent tune-up by a first rate mechanic 
didn't change anything (I thought it would so I didn't bother mentioning the
problem).

At first I thought it was an air-in-the-fuel-line problem, because the carbs 
weren't the highest point in the system, but replacing and redressing the
lines didn't seem to help.  I checked the pressure from the electric fuel pump,
and it seems to be within spec (4-5 psi).  The car does have an in-line fuel
filter, which I do not believe was part of the original fuel system.

Any ideas?  The car has ~80K miles, with a recent engine overhaul.  It
has Weber 40IDTP3C carbs (stock) with possibly larger than stock main
venturi and '120' main jets on a 2.0 liter 911T motor with the
original Marelli distributor.  The car had an uncertain history prior to
1 year ago, but the mechanic who overhauled it claimed that the cam timing
had been advanced 6 degrees for more low end torque.  I can't recall
how long it has had this problem, but it has probably been there in some
form for as long as I've owned the car.  It seems to have gotten worse in
the last six months.

Lee Hasiuk
{ihnp4, ucbvax, decvax}!trwrb!trwspp!spp2!hasiuk