Folks,
I’m trying to diagnose and fix a drivability problem with my 1974 2002 – a hesitation that occurs in very specific circumstances. The car has over 150,000 miles without a motor rebuild. The current carb is a 38/38 Weber, installed by a prior owner.
This is the issue. I autocross the car, which means that it sees a series of 30 second to one minute runs in first and second gear at relatively high RPMs. For the first two or three runs, all is well. Once the motor has warmed up (the temp gauge is reading above the blue zone but not above half-way) I get an intermittent lack of power for the first 15 seconds of the run. The car launches well, and I short shift to second before hitting red line in first. Then I get about 10 to 15 seconds where throttle response is erratic and the car seems to have much less power when I ask for it. After that, the problem goes away for the rest of the run. An autocross course is by definition twisty, but I can’t association the problem with specific lateral accelerations or hard braking. Nor do I hear any obviously missing ot backfiring from the motor. For the next run (and the next and the next, assuming that the car had not cooled down), the problem persists in exactly the same way. The issue only occurs in this context – never in driving on the street in any gear at any speed, and never in the later parts of an autocross run.
When I first got the car (a couple of years ago), it had an occasional rough running issue in street driving, particularly under acceleration. Since then:
-- I had a compression test performed, which showed no issues,
-- I replaced the spark plugs,
-- I replaced the distributor with an Ireland Engineering unit with an electronic ignitor,
-- I replaced the ignition coil,
-- I had the carb checked for blocked jets, etc., which showed no issues,
-- I replaced the ignition wires with an Ireland Engineering 8mm set.
The prior owner had had at least some of the fuel lines replaced after they clogged. I don’t know if the fuel pump was replaced at that time.
The new distributor and coil cured the minor drivability problems on the street, but didn’t solve the issue on autocross runs. The two most puzzling things (to me) about the problem on autocross runs is that it only occurs after the motor is warmed up and it only persists for the first part of the run. I would be very grateful for any ideas as to what could be causing this issue.