Refresher Course, Please: Vacuum Advance Line Bolcked Off?

[70bigblockdodge]

Kevin (twostick) is correct it is ported above the throttle plates. The hose connected on the driver front near mixture screw should go to vacuum canister. Your choke pull off needs a hot 12 volt ignition source put to the other blade connecter then it will heat up and open the choke allowing the car to keep running.

 

[Boomer]

Okay, thank you. I plan to change the filter and make a jumper for that connection this weekend, provided there is juice there. Easy to check with the DVM. I'll report back the results. Already tried hooking the vac line back up and the car threw a fit, so there's more to look at there. There's also a pretty poor excuse for a cap on the other vacuum nipple to the left. Feels like an old cigarette filter wrapped in electrical tape.

 

[70bigblockdodge]

You need to send 12volts to the connection the one that is connected is the ground. Get that operating and then we can get your timing sorted.

 

[Ripinator]

That would not be correct, as ported vacuum always follows manifold vacuum only (except at idle), and as airflow increases, that means generally that manifold vacuum decreases. Only vacuum taken in the neckdown or venturi area increases due to an airflow speed increase and nowhere else in the carburetor body bore. That is why I think you need to take some time out and rethink how the distributor advance works. You will get there.

I sure am glad you guys are having this discussion. The vacuum advance thing has been a mystery to me for many years. At least now, I have some understanding of the differences between manifold vacuum and ported vacuum and how and why each is used. Hell. . . I never even heard of "venturi" vacuum, so I guess if my car has no EGR, I don't need to worry about it. Thanks again guys.

Rip

 

[The Horvaths]

We are all in this hobby with C bodies together, and I think everyone deserves respect and patience no matter what. Helping each other is what it is all about. I get stuff wrong sometimes too. You are very welcome!

Steve

This attitude is exactly why I am a repeat visitor to this forum. Awesome education in a near-arcane art without emotional flamboyance. You guys rock. Thank you for being you.

 

[livininharrow]

This attitude is exactly why I am a repeat visitor to this forum. Awesome education in a near-arcane art without emotional flamboyance. You guys rock. Thank you for being you.

x 2

 

[Boomer]

You need to send 12volts to the connection the one that is connected is the ground. Get that operating and then we can get your timing sorted.

I tried it but need to investigate a little deeper. According to the DVM it only has a .13 - .16 volts at the connector. Double checked and it was set to the 20 volt scale. Weird thing is, it still seemed to help. After changing the filter and hooking up a temporary jump to the choke, it idled like a new car.

Here's a short video of it running last weekend:

https://youtu.be/woYS0yImX1I

One thing I noticed - it gets VERY hot in that engine bay. To the point that the radiator bulkhead is hot to the touch, way over at the yellow stickers. The new fuel filter was very hot as well. Wondering now if that's what caused the old filter to deform? Figured it was caused by good ol' ethanol sitting in it long term.

You can see where a former owner threw a quick kludge on the heater inlet and outlet on the front of the block. The hose is too small and pinched in half, so that needs to be dealt with next. Whoever it was taped up a leak with black duct tape.

 

[70bigblockdodge]

Send 12 volts into that terminal where the green jumper is connected and the choke will open after a few minutes when the element heats up the spring inside that black circle. Buy lots of spare fuel filters because you are going to clog up alot of the with that crap in the tank.

 

[Boomer]

Yep, when I saw that rust slurry in the filter I knew the tank needed to be cleaned out. The next big project. Wouldn't surprise me though if the new filter was already plugged by then. At least this one should keep it from getting to the carb.

Not sure what's up with the voltage at the connector, need to trace it out in the wiring diagram. Very little voltage at all. Maybe it went to something else, just seems ironic that it's located right behind/beside the choke. It's possible there's a bad connection somewhere supplying it.

Hope to get more time with it this weekend.

 

[1970cat]

your car did not originally come with an electric choke so the wire must have went to something else.

 

[Boomer]

Interesting! That's good to know, thanks very much. Will look around and see if there is anything else back there like a sensor with a single blade that the connector fits. Someone did tape up the harness with electrical tape so I suppose it could've been added. If so, it wasn't done to fit this carb.

This weekend might end up being a good time to dig into the electrical issues a bit deeper.

 

[70bigblockdodge]

You will have to run a separate ignition hot to that connector. Your car was a divorced choke car, heat expanded a spring in a well on the intake manifold crossover, which opened the choke plate.

 

[Boomer]

That linkage is still there, right behind the electric choke. Just nothing to hook it to.

Supposed to rain all weekend so I may not get a chance to play with it more, but will study the wiring diagram in the manual and see what is waiting to be learned. Really curious to see what that empty connector should be hooked to. Think it has a brown wire.