I recently purchased a 79' pickup with the 20r engine. Initially, it was running perfectly, but on two separate occasions while idling, the tachometer would start going crazy, and the car would start sputtering, trying to stay alive until it eventually died. I figured it was a tuning issue and took it to get professionally timed and get the mixture dialed in, but after doing this, the problem has become more frequent to the point that it only takes a few minutes after starting driving before it starts. I've replaced the fuel filter and tried to adjust the mixture further but nothing seemed to work. I discovered that the secondary in the carb isn't opening at any rpm, and also doesn't appear to have any fuel going to it. I plan to rebuild the carb (Webber 32/36) to clean it and replace the seals in case it's gunked up or has a vacuum leak. I'm hoping this will solve the issue, but it's starting to get pretty discouraging, so I'm wondering if there's anything else it could be.

Here is some additional info about the car: the emissions and EGR system have been deleted, and the carb and entire upper half of the engine were rebuilt in the last five years, so it is fairly new. I have videos of the secondary valve not opening, and I have a video of the tachometer and engine while this issue is occurring. If you would like to see any of these, I can send them to you, or I'll figure out how to upload them because they are large files.

I really appreciate all the help/ advice that yall can give me.

 

Sounds like a vacuum leak somewhere. Connect a vacuum gage to a manifold vacuum source. (anywhere below the throttle plate). See what your getting for a reading at idle.

If your Weber has the two piece manifold adapter, they are famous for vacuum leaks. Try spraying some silicone lubricant at the base of the carburetor and adapter plate while the engine is running. See if the idle improves.

 

I believe that it's a 2-part adapter, no? Also, forgive me, I'm new to this, how would spraying silicone lubricant help?

 

That the shitty 2 piece. They all leak. I’ve had to reseal mine twice.

when your engine is running, vacuum is actually a “suction motion”. Silicone spray is non flammable, and will temporarily seal any leaks. If you notice an increase in rpm immediately after spraying the suspect area, you’ve found a vacuum leak.

You could use any type of spray that’s compatible with a gasoline engine. I like silicone because it’s safe to use around hot components.

A vacuum gage will really help also. It’s a good thing to have in your tool kit. Harbor freight sells them very reasonable. You might also find one from a tool loan program such as AutoZone.