After doing some reading the below picture seems like pertinent info as well. It shows the plastic tree (blue) with one vacuum line connected to intake manifold just below the front of the carb, a vacuum line going to heater core, and a plugged port.

It also shows the vacuum line that goes from transmission to manifold vacuum port of the carb (yellow) and the unplugged line I never noticed (pink) that goes to intake manifold below the carb on passenger side.

Pretty sure some or all of these vacuum lines are not correct. Just hoping to figure how to route everything correctly and what should/can be plugged.





It may also be relevant to know that the previous owner removed the AC. It originally did come equipped, but the previous owner removed the components.

 

The manifold vacuum can be pulled from many different places and still work. For instance, if you would like to pull the line going to the front of the carb to the transmission off, pull the cap off the plastic manifold on the firewall, and cut the rubber line shorter from the transmission and run it up to the plastic firewall manifold, you can, since you said the blue line goes to the manifold vacuum to feed the plastic firewall manifold. You would then put the cap you took off the firewall plastic manifold on the vacuum port you just unhooked on front of the carb.

But more importantly, if you want a rock solid steady idle, in gear or out of gear, take the distributor vacuum line off the manifold and cap that manifold connection. Then run the dist vacuum line around and plug it into the timed vacuum port. Get it warmed up, it may not want to idle, the idle speed may be too low. If that is the case, turn the curb idle screw up till it idles. Once it's warmed up, pull the dist vacuum line off the front of the carb, there should be no vacuum on that timed port. If there is, turn the idle speed down till it goes away. Once it's gone, plug the dist back in, adjust both idle mixture screws till you get the highest idle. If the idle goes too high, turn the curb idle speed adjuster back a little bit and keep on adjusting the idle mixture screws till it idles the best.

Then drop it in gear, it should hold idle speed a lot better than it did before.

 

Ok this all makes a lot of sense.

Any thoughts about that one unplugged port/line that I circled in PINK that connects to passenger side of the intake manifold? Should I plug that? Any ideas what that was for?

 

Yeah, cap that poor thing. Regardless of its original purpose, you should not have an open vacuum line like that.

With the engine running, can you feel suction there? I vaguely remember a line in that area for heating the factory choke. IIRC, the line wasn’t actually connected to manifold vacuum. It was from a funky little heat chamber in the exhaust crossover passage.

If vacuum is present, cap the line and you’ve found a major cause of trouble with the idle speed. If vacuum is not present, cap it anyway but it wasn’t causing any problems.

 

Well, bad news… I did everything advised and there was no improvement. Connected timed vacuum port on carb to the distributor, plugged the manifold vacuum port on the carb, and moved the transmission vacuum hose to a port on the intake manifold. Also capped off the other random port and replace another cap on the intake.

All of the above didn’t really change anything. The truck drops like 400 rpm when going from park or neutral to drive/reverse. Also the surging/revving didn’t go away it’s just still intermittent. I drove it a few miles just to see how it acted and it stalled out several times. Usually when applying brake and turning the wheel at the same time. By the time I got it home it wouldn’t even stay running in park. It seems like hills have an affect on it as well.

I took a video linked below before I went for my drive. I’m at a loss here. I’ve played with the idle screw and idle mixture screws for hours and at times it idles perfect (but still drops about 400 rpms). I can say this, I’ve had all these symptoms before and it was the carb. I replaced it and it ran great until it sat for the last 6 months bc of the bad distributor pickup coil. I’ll also add that that I rechecked the timing again today and it’s right at 10 before TDC.

 

Pull and plug the vacuum line to the dist. and see what happens?
Have you checked the float level in the carb?
Kind of hard to hear it with the sound turned up all the way on my laptop.
Dave ----

 

Ditto! I was going to suggest the same thing. Again…

Also, has the centrifugal advance mechanism been tested? It’s easy to do with a timing light. See post #3 for details.

 

I did pull and plug the vacuum line to the distributor when I made the changes to recheck the timing. The idle didn’t change much but there was some slight sucking before I plugged it.

Checking the float level would be a new one to me. Any videos on how to do so? I don’t even know what a float level is… still learning as I go.

 

Did you try a test drive with the line disconnected and plugged? It’s safe to drive like that. Maybe not forever, but it’s fine for a test drive.

 

I will have to look over your pictures to see what carb you have. If it's a Holley it's pretty easy.

As Karl said pull the hose, doing hook it back up, plug it and drive it.
You can drive it for ever and not hurt anything you just dont have all the power it may give you.
I just removed and plugged mine as I have a pinging issue I am trying to get a handle on. Put 30 miles on it today and will put close to 80 tomorrow to / from work.
Dave ----

 

Oh that line to the dist should not have vacuum on it at idle.
If it dose it is either hooked to the wrong port OR the idle is set to high and making the port get vacuum.

Dave ----

 

Well I had your words in mind when I did this and I hate to say that it’s definitely not on the wrong port and I tried lowering the idle and it was still sucking below 800 rpm in park. I couldn’t get it to not suck…

 

I did not but I can… I guess we’d hope that cures the surging and stalling?

 

Well, that sucks!

https://m.youtube.com/watch?v=2Lya292wdpo


For the moment, don’t worry about the presence of vacuum in that line. Concentrate on what would happen if vacuum wasn’t there. In other words, disconnect and plug the supply side of that line.

If you see improvement, then you’d know you’re hot on the trail.

 

From your video I can see that you are having a surging issue. Does the surging only happen at idle RPM? When you open the throttle does the surging smooth out? At what rpm does it smooth out?

How is your fuel pressure? Does it surge following a similar pattern?