Q: I have an engine with a two barrel carburetor. It appears to me the 2nd barrel isn't opening. When and what opens the second barrel?

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The truck idles pretty good when the engine is cool. It begins to run rough when up to temperature and is very slow to respond. I've cleaned the inside and outside of the carb with carb cleaner and I've cleaned and replaced vacuum lines and connections. I've also changed plugs and wires. I'm baffled! Thanks for considering my dilemma.

respectfully, Jim Burquist

My car has 200000 miles.
My car has a manual transmission.

Hi there. On two barrow carburetors, there are two ways that they open. The most common way is through engine vacuum. When the vacuum drops to near zero, the secondary throttle valve will open and operate the secondary jets. Other systems have a mechanical throttle that opens as the throttle is pushed down far to the floor. Check the vacuum hose or linkage to the secondary and make sure that its hooked up. If your vehicle has a vacuum line to the carburetor and there is no vacuum leak, then the diaphragm in the carburetor could be split causing the plunger to not function making the accelerator pump fail on the secondary circuit. If you need further assistance with your secondary throttle on your carburetor, then seek out a professional, such as one from Your Mechanic, to help you.

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