Adding a second carburettor on your Chevy 235 adds muscle to the stock six-cylinder engine. The job is not complicated, providing you have some wrenching expertise and talent for making things fit. The easiest part is bolting up a dual intake manifold and installing a second carburettor that matches the original, or installing bigger carburettors. The challenge is adapting dual fuel lines and dual carburettor linkage. Pull the old manifold and carburettor off and get a dual manifold that works with the exhaust headers. Decide on the engine upgrade you want and use a pair of matching carburettors.
- Skill level:
- Moderately Challenging
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Things you need
- Haynes or Chilton repair manual for your Chevy
- Standard gauge tools
- Dual intake manifold
- Intake manifold gaskets
- Torque wrench
- Carburettor studs with locknuts
- Carburettor gaskets
- 2 carburettors
- Fuel pump adaptor
- Rigid fuel lines and fittings
- Dual linkage
Set up the dual intake manifold with two bolts in each flange and an intake gasket on the face of each flange. Position the manifold at the cylinder head and thread the bolts into the head by hand. Torque the bolts to 18 foot-lbs. each using a torque wrench.
Thread new carburettor studs into the holes at each side of the carburettor ports on the manifold. Place a new carburettor gasket atop each port on the manifold.
Remove the air cleaners from each carburettor and set the air cleaners aside. Turn each carburettor so the throttle linkages are facing in, toward the rocker arm cover on the engine.
Align the holes in each carburettor flange with the carburettor studs on a manifold port and set the carburettors in place on the intake manifold. Thread new locknuts on each stud by hand. Tighten the nuts securely with an open-end wrench.
Manifold and Carburetors
Loosen the existing rigid fuel line fitting at the fuel pump and remove the rigid fuel line. Attach the dual fuel line adaptor to the fuel pump and tighten the fitting.
Attach a length of rigid fuel line to each side of the adaptor and tighten the fittings. Position the other end of each line near a fuel intake fitting at a carburettor. Thread each fitting into place on a carburettor by hand. Tighten the fittings with an open-end wrench.
Turn the throttle stop screws on both carburettors fully closed with a screwdriver. Back each screw out 1 1/2 turns as a preliminary setting. Position the dual throttle linkage at the outer edge of the carburettors. Connect each linkage rod to the corresponding throttle levers using linkage clips.
Attach the end of the dual linkage to the existing accelerator linkage in the engine compartment. Ask an assistant to push the accelerator pedal to wide-open and let up several times as you visually ensure that the linkage moves each carburettor throttle lever to full-throttle simultaneously.
Follow the procedures in your Haynes or Chilton repair manual and adjust the idle and fuel-air mixture on each carburettor. Adjust the throttle stops as described in the repair manual. Reattach the air cleaners on each carburettor.
Fuel Lines and Linkage
Tips and warnings
- Edelbrock or Holley racing manifolds might not work with stock exhaust headers.
- Synchronise the carburettors using a monometer.
- Install in-line fuel filters at each rigid fuel line.
- Secure the dual fuel lines at one or more places with rigid tubing brackets.
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