352/3spd, bone stock.

When I bought my truck the carb leaked gas so bad it was a fire hazard.

I had to use Belzona on the fuel inlet to get the leak stopped, the float was stuck, but otherwise it wasnt in bad shape.

The idle was way to high, but it was the only way I could keep it running. I also had to have a small amount of choke on all the time.

The truck would never come up to temp (according to the gauge), so last month I decided to check the thermostat when the upper radiator hose blew out. Turns out the thermostat slipped when the PO installed it and it wasn't seated in the housing, so in effect, there was no thermostat.

With a new thermostat the truck comes up to temp and I was able to close the choke.

Tonight I attempted to adjust the idle, I went for a quick spin to get up to temp. When I started, the vacuum reading was 20 inches. As soon as I dropped the idle speed, the vacuum gauge dropped to zero. I played with the timing, but there was no change on the vacuum reading.

I ended up closing the 2100 adjustment screws all the way in, then backing out 1.5 turns, I dropped the idle to where it was smooth, and adjusted the timing by ear for the best idle.

Does the zero reading on the vacuum gauge indicate a intake manifold leak?

Although the gauge reads zero, the power brakes work fine, the truck idles very smooth, and seems to have plenty of power. I made a jaunt to the gas station for a fillip, all seems well.

After installing the thermostat, on a hot day when I shut the truck off it would diesel. I thought the timing was off. I will see if it still diesels over the next couple days.

 

the vacuum depends on where you have it plugged into the carburetor it will either read 0 at idle or it will show a level of vacuum.
As for it running on after you shut it off, pull one of your spark plugs and look down inside and see how dirty the top of the piston is. They may be carbonated up. If it is, there are things you can use to help clean it up.

 

I install my vacuum gauge on the manifold when tuning. Seems to work well for me.

 

Sounds like you have the gauge connected to spark or timed port on the carburetor.

The gauge needs to see manifold vacuum. When setting timing make sure vac advance is disconnected and plugged. Adjust the idle to spec or 50-100 RPM lower and then, adjust timing for maximum steady vacuum; back off 1 or 2 inches of vacuum and tighten the hold down clamp on the distributor. If you have a timing light, you should optimize the timing curve by measuring the total distributor advance. Most stock distributors have too much total advance and heavy, stiff springs that slow the rate limiting the amount of initial that can be brought in.