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MaxChlan

Distributer Constantly Advanced

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I've been running into a small issue with my 86 720. It seems as though there is a constant vacuum on the vacuum line to the distributor. I'm curious to know if anyone as simply plugged the vacuum control valve and thermal vacuum valve (I think this is the source of the problem), and just ran the vacuum advance right out of the carb. It seems to idle/run better when I simply pull the line off the distributor (right at 800 RPM, super smooth), but I lose performance at highway speed as a result. I currently have the EGR plugged (I had to cut it when I did the head gasket), which may also be a culprit. I checked the plugs, wires, and looked for other vacuum leaks and found no issues. Any advice is appreciated!  

 

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Edited by MaxChlan

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Follow the vacuum advance line back from the distributor and make sure it goes to the proper places on the diagram. If still getting vacuum disconnect the hose to the TVV and the vacuum control valve and run directly to the port on the carburetor.

 

There's a good chance the vacuum advance is mistakenly connected to the bottom canister vacuum line to the intake.

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So, I did some inspection, and all of the vacuum lines are running to the correct places, so I think. This is where the vacuum line for the distributor connects to the carburetor currently. This port seems to be pulling a strong vacuum constantly, so maybe this is incorrect. When I plug this port, the idle drops quite substantially. When left unplugged, it runs at a good idle. I should note too, that when it is connected to the distributor, it runs *fine*, but the idle is a bit low, and if it sits for a bit, the idle drops to 500-600; a little bit too low. Timing is currently set between 2-3 degrees advanced per the FSM.  I'm back and forth on simply doing a Weber swap and calling it done. I seem to have mixture issues on start up, and I think a lot of the problems would be solved with a swap. 

 

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Edited by MaxChlan

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Doesn't look like it's to the carburetor. Should be on the carburetor base.... like the other one in the picture on the left.

 

YKeynHt.jpg

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So, I think I figured it out. That port goes to the vacuum switch up above, which I had incorrectly in the vacuum advance to the carb. I flipped those two, and it seems to have solved the problem! I made a slight ignition adjustment, replaced a vacuum line, and now it seems to run much better!

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