Carburetor Fuel Jets & Power Valve Swap - More Flow - CHP Step By Step

Open the Bowls For Extra Muscle

Sean Haggai Sep 1, 2009 0 Comment(s)
0909chp_01_z Carburetor_fuel_jets_power_valve_swap Carburetor_modifications 1/12

For some, dancing around the carburetor like a trained performer is second nature. These tuning wizards wield a flat-blade screwdriver like a trusty sword. Before you know it, the changes are made and the car not only sounds healthier and runs cleaner, it rips. On the other hand, some look at the carburetor and avoid it like the plague. To be honest, it shouldn't be that way. Carburetors are simple to wrench on, and changes can be made in a matter of minutes. The good thing is those changes aren't final.

If you make the wrong change but have kept track of what was adjusted, you can always go back to square one.

While this may seem like a refresher course for the wrench-happy, remember that we were all rookies at one time. Learning the basics on carburetor function should start with jets and power valves. Not only are these swaps simple to complete, but gains can be had almost instantaneously. For jet changes, the carburetor can either run rich or lean depending on what size jets are installed. The higher the number, the more fuel will flow, and vice versa.

0909chp_02_z Carburetor_fuel_jets_power_valve_swap Edelbrock_performance_intake 2/12

For the best view possible, we set the Quick Fuel Technology Super Street Series 735-cfm carburetor on a small-block Edelbrock Performer intake manifold. Normally on a running engine, fuel would fill the outer bowls. We began on the primary side of the carburetor (facing radiator). Using a 5/16-inch box wrench we loosened and removed the lower corner bolt first. This allows for any remaining fuel in the bowls to drain out. Then we removed the rest of the surrounding bolts to take the bowl off.

For power valves, the same idea applies. For the street, power valves are a necessity since most street-thumping is handled at part throttle. The importance comes when the throttle is opened up. Additional fuel is needed for a safe air/fuel ratio. In wide-open throttle situations, vacuum in the intake manifold drops to almost zero. At this point the power valve will open and allow more fuel (along with main fuel jets) to the carburetor.

To illustrate these ideas, we grabbed up a Quick Fuel Technology (QFT) carburetor. While QFT also offers blow-through carburetors, E85, alcohol, and custom class carburetors, we opted for the Super Street Series 735-cfm to showcase our efforts. The methods for changing fuel jets and power valves are broad and apply to the rest of QFT's lineup of carburetors. We went through and pulled the bowls off the carburetor to demonstrate the proper method of swapping jets and power valves.

Quick Notes
What We Did
Detailed the swapping of fuel jets and power valves

Bottom Line
Jetting and power valves give you more power and efficiency

Cost (approx)
Jets: $4.89 a pair
Power Valves: $6.32 each
Carburetor (PN SS-735-VS): $519.73

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