TECH BULLETIN

Inlet line vacuum leaks can prevent the Race Pump from priming and cause erratic fuel pressure. If you are having trouble priming your fuel system, the system looses prime after sitting or the idle fuel pressure is erratic, there is an easy way to test your fuel pump.

Replace the inlet line with a short line inserted into a 5 gallon fuel jug.

On carbureted systems, fill the carburetor float bowls and fire the engine.

On EFI systems spray fuel into the air inlet while you fire the engine.

If the pump primes up and the pressure is steady….you have a vacuum leak between the inlet side of the pump and the pickup in the fuel tank.

Pressure testing the inlet line will not work….you must vacuum test it. A line that will pass a pressure test can still have a vacuum leak. Be sure to wiggle the lines and fittings while you have a vacuum on the system. An intermittent vacuum leak can be a real puzzler.

The Race Pump is more sensitive to vacuum leaks at cranking speed and low RPMs than traditional diaphragm pumps. The Race Pump is a small, high RPM pump. Diaphragm pumps are large, low RPM pumps. At cranking speed and idle the diaphragm pump’s displacement is up to 10 times greater than the Race Pump. (At high RPMs the Race Pump’s effective displacement is much greater than the diaphragm pump) The diaphragm pump can easily overcome a vacuum leak at cranking speed and low RPM. However, the vacuum leak will reduce the diaphragm pump’s output at higher RPMs. The Race Pump, being a small displacement – high RPM design, cannot overcome a vacuum leak at cranking speed and low RPM. A vacuum leak is detrimental to both style pumps. The Race Pump just makes it more apparent, allowing you to correct it.