Hey,
Most problems fall into three categories.
First, if the vacumn diaphram is shot, then the secondaries are not opening. You cannot test this on the motor since the secondaries only open under load, not from reving the engine. To test, you should hear a suck and click sound when going from full throttle acceleration to normal driving. If you hear no sound, the diaphram is gone or someone has removed the bleed ball bearing from the vacumn canister. A replacement diapram is $8.00 or so, and I would recommend going with a quick change top so you can exchange springs without major disassembly. Make sure that the ball bearing is in the vacumn canister, otherwise the secondaries will remain open after your full throttle activity instead of closing properly. THIS IS NOT GOOD.
Second, my Mustang makes 414 hp and I use the latest opening BLACK secondary spring. WHY? Because I am using 2.5 gears right now, and if the secondaries open too fast the car just lies flat and does not come on until the engine labors up to 5,000 rpm. If the engine is running flat, there is a chance that you have the secondaries opening too soon. Go to a heavier spring. They are colored and run light to heavy in this order: white, light yellow, dark yellow, purple, silver, brown and black.
Third, you may have an internal or external vacumn leak or more commonly the PVC tube or valve might be SHOT. Replace both the PVC and the tube and test the engine with a vacumn guage. If you are pulling air in from under the intake, you will spend months trying to get the car to pull under throttle and nothing ever happens. Make sure you check the torque on your intake manifold, and then very carefully spray starting fluid on everything that transports vacumn. If the engine picks up rpm, you found the leak. I alway check at the base of the carb and the throttle shafts. Remember that a bad pvc valve or pvc hose can wreak havoc with accelleration, so always check this FIRST.
Try these and email me at
jim_howard_pdx@hotmail.com if you have additional questions. Make sure to leave me a return email address. I do not check this website more than once every other week.
Jim