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

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Primary carbs are identified by the small vacuum advance

Primary carbs are identified by the small vacuum advance

The 140Hp Engine

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

Unlike the 110Hp (where you have only two primary carbs), 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 the full vertical position. Use a .160” feeler gauge and measure the gap between 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 the choke rod up until travel stops and adjust the rod until the bottom of the rod is even with the top of the hole in the choke lever. Connect choke rod and repeat operation on another choke.
  4. Disconnect the left and right secondary carb actuating rods, and 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 enter the hole in the 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), and verify that all carbs reach vertical position (full throttle) simultaneously. If not, continue to adjust and tweak.
  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.

This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.