MANLEY THERMOQUADS secondary mystery

[@chumleye1112]

Excellent description of operation and basic trouble shooting of the secondaries operation.

[@larryhutchens7593]

The thermoquad works very similar to a quadra jet. That spring tension has a factory pre set value that is on the rebuild sheet or in the factory shop manual. The secondary air valve opens at a specific rate depending on the bleed down rate of a vacuum diaphragm on the opposite side of the carb from the pre load spring. The manifold vacuum holds the secondary air valve closed by way of this diaphragm. If you doubt this just try to open the air valve while the engine is idling, provided the diaphragm is not ruptured. You can force the valve open but it is difficult. There is a built in restriction in either the diaphragm itself or in the vacuum port that the diaphragm is connected to. I have several of those thermoquads & some have it one way some another. That method of air valve adjustment will work but it is kind of a quick down & dirty way of doing it. Additionally the extra spring tension will mess up the fuel metering at wide open throttle. A ruptured diaphragm is the most common cause of the bog situation. Simply check it with a vacuum pump & see if it will hold the valve closed. There is a very good instruction manual on the quadra jet by a guy Named Cliff Ruggles & he explains the function quite well. It is worth the cost.

[@josenevesneves7880]

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