How to Synchronize Secondary Carbs in the Corvair 140 Hp Corsa Motor

Updated on May 27, 2018
perrya profile image

Perrya knows a fair amount about the Corvair, America's aluminum-engine classic car.

Primary Carbs are identified by the small vacuum advance.
Primary Carbs are identified by the small vacuum advance.

The 140Hp engine has four carbs. The major differences between it and the 110 Hp (two carbs) is that the 140 Hp uses a different cam, it produces different torque, and the engine heads are different.

Unlike the 110 Hp, where you have two primary carbs only, the 140Hp has two primary and two secondary carbs. The primary carbs control the secondary ones, which provide more power around 40+ mph; below that speed, you are operating with only two primary carbs. The 140 engine is usually found in a Corsa or a 1967-69 Monza. The Corsa was only made in 65-66.

The secondary carbs are slightly different as they have no idle mixture screw and some have no accelerator springs inside. But the Venturi cluster and jets still need to be free of clogging. There is a lockout lever on the side which is operated by the primary carb chokes. Before any secondary synchronizing can be done, you must have the primary carbs synchronized and adjusted correctly so both throttle plates in the bottom of the carb open and close at the same time, as do their choke plates ( located at the top of the carb), otherwise, synching the secondaries is a waste of time. The secondary carbs have a Lock-out lever that prevents the carbs from activating during warm up.

Assuming the primary carbs are in synch:

1. Disconnect choke rods.

2. Open the left primary choke valve to full vertical position. Use a .160” feeler gauge and measure the gap between the the lockout lever and lockout tang. It should be .160”. Bend to adjust if out of spec. Do this to the right side primary and secondary also.

3. Hold choke valve closed and actuate the accelerator cross shaft to set fast idle cam. Turn and pull choke rod up until travel stops and adjust rod until bottom of rod is even with top of hole in choke lever. Connect choke rod and repeat operation on other choke.

4. Disconnect the left and right secondary carb actuating rods, hold carb cross-shaft so primary carbs are in full throttle open (throttle plates are in vertical position).

5. Make sure the choke valves are closed (secondary throttles are locked out). Adjust secondary carb actuating rod so its spring is fully compressed and clevis will just enter hole in cross-shaft lever. Now, back off counterclockwise, 2-3 turns. Repeat this on the other actuating rod.

6. Connect both secondary actuating rods and with both choke valves wide open (vertical position), rotate carb cross-shaft to full throttle (plate is vertical), verify that all carbs reach vertical position (full throttle) simultaneously. If not, continue to adjust and tweek.

7. With choke valves closed, rotate carb cross-shaft to full throttle and check primary carbs. Verify they reach position simultaneously. Verify that the secondary carbs are locked out and the actuating springs are fully compressed.

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    • profile image

      Robby 

      8 years ago

      i have a 1993 corsa, and it keeps cutting out everytime im stop, the car can be out of gear and my foot on the clutch but it still happen. do you have any ideas what the problem can be?? thanks

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