Vacuum Issues?

My Vans been running great until recently it felt like it would bogg down under any load; off the line or up hill. Once it's up to speed, it's fine...
I checked and noticed that there was a vacuum stem on the carb that had nothing connected to it.


I tried capping this stem, redid timing and now it kind of sputters under load and does not pull at all going uphill with some small poppy backfires. Again, once the vaccum advance kicks on it picks up speed and once up to speed it's ok. What should be plugged into this, or should it just be capped off? Does this sound more like a timing issue? Or maybe a carb issue?

All my vacuum lines are going to the right places as far as I know. PCV directly to manifold, transmission to lower inlet below carb, and distributor right above that which is ported.


Thanks guys!

That thing could have been plugged before? Because it was running smooth until that thing became apparent. There was a hissing noise and that thing was just sucking air, so I plugged it.

I will check the fuel flow inside the carb. Should I be checking it with the car running? Should I be getting a spray or a stream of gas?

Thanks, Don!

Took me awhile to get around to checking all this. With the motor off, it looks like there's a healthy stream of gas coming out of the accelerator pump...running it kind of dribbles (don't know if this is normal, just because of the vibration of the motor or what?)
Could I have a clogged fuel filter/line, or something up with the fuel pump?

Im also gonna check that vacuum advance that we put in there when we put the new dist. in.

I will keep exploring, but in the meantime, any suggestions on what to check for?

Thanks!!

Sounds like you are barking up the wrong tree.
It started running poorly, and you find a vacuum leak.
A leak that small will not cause the big symptoms described. Maybe a bit of hesitation off-idle, but that's it.
Do you still have point ignition? When was the last time you serviced it?
These old motors require regular maintenance that many people aren't used to with modern vehicles.
Go back to the basics and check the dwell, timing and carb adjustment. If the dwell is off much, replace the points and condenser. Pull the plugs and check them. I tend to change them, but if they aren't worn or fouled, you can stick them back in.
Check the cap, rotor and see if you get a healthy spark.

I have a new electronic ignition installed on the van, and it ran fine up until now.
Pulled out the fuel filter, which on this carb is a screen retained with a spring. It was actually pretty dirty, so I cleaned it out real good and reinstalled. This didnt change anything.

I will check my plugs next and see what condition they're in. Now Im almost thinking it feels like a timing issue, although Ive checked the timing multiple times and it seems OK (unless Im doing something wrong). Had sort of similar feel when my timing was off once before.

To recap the problem, it hesitates like the first half of first gear if Im giving it some gas. Top end feels like it's lacking power too..not pulling like it used to.

Is there a more serious problem that could cause these symptoms? Its running at a nice temp, idles smooth, and cruises smooth once its moving.

fuel starvation?? yet limited ?
fuel pump ? smell the motor oil -fuel??

Don, I owe you a vacuum advance! Thank you for the loaner.

I will try the fuel filter and check the timing again. If I cant get any results, I will take you up on that GM Distributer offer.

Thanks for your help

So, while crawling around under the van, I noticed that the vacuum line that connects to the transmission had been pulled off and was really loose when connected. Got that all clamped down good. Also noticed that two of my exhaust manifold bolts were loose, so I tightened those down as well.
It actually seems as though it may have fixed the problem! However, I did install a clear inline fuel filter. Right after i installed it and fired it up, fuel rushed in there and it stayed full at idle. Just took it for a drive and now its not full and look like there's only a trickle coming through. Van still seems to idle fine though.

Scotty - get a ton of fire insurance coverage on that nice van you had-weve all been over & over those clear plastic fuel filters-#1 Fire Hazzard!!

I will probably just get rid of it once I'm done testing the fuel system. Thanks for the heads up!

Still feel like Im having some issues with my van. It feels sluggish when trying to get up to freeway speeds, especially if there is any kind of hill. Or if Im cruising on flat ground and start heading up a hill, it just kills my power. I could be flooring it and it takes a really long time for it to get back up to speed.

Maybe it's just the limitations of the 2-speed powerglide, but I swear I had more power before. It used to pull up hills pretty well.

The only things that are the same since the motor swap are the HEI distributer and the transmission. Timing is set and dist is getting advance when it's supposed to...Could it be something with the tranny?

What do you guys think? Am I just crazy?

Sounds like a good idea. I don't have a vacuum gauge to test that...How can I test the modulator and check for proper kickdown adjustment?