Mysterious Vacuum Looking Device Behind Carburator?

[Duncan]

Still a newbie at my first owned Bronco. I just rebuilt engine, the whole nine yards. We have put everything back together, except none of the people helping me (Chevy folks), know what the cylindrical vacuum device that sits behind the carburator.

What is it?

Can someone tell me how to hook it back up correctly?

Could this device be the reason my Bronco feels like it's in 3rd gear starting out? Everything seemed fine after we fired it up and ran it for 30 minutes to break in the engine. We adjusted the timing and all and everything seemed perfect.

1 week later, after getting all the wiring resecured and changing the oil, it sounds fine upon starting, but runs like it's in 3rd.

Please help!

Duncan

 

[Bronco717274]

That thing is your EGR valve, don't think that's what your problem is. What size tire's are you running.

 

[julzrulz]

(Not trying to hi-jack the thread!)

I'm in the same boat w/ you Duncan-

Just installed a 306/rebuilt C4 & Dana 20 in my 73 EB a couple days ago and have the same ("3rd gear feel") symptoms.

Bronco717274- I think I know where you're going w/ that question. I tossed BFG 35/12.50's on mine and know I MUST re-gear my rig ASAP! 3.50's (?) are a bad idea w/ bigger tires!

 

[Bronco717274]

Big tire's 3:50 gear's there's your 3rd gear feel.

 

[Duncan]

It's not the tires.

Big tire's 3:50 gear's there's your 3rd gear feel.

I'm running the same tires as before, when it ran. They are 31.50 (little guys). Any other ideas.

Can you tell me the configuration of the EGV valve? I appreciate your help.

Duncan

 

[Pa PITT]

duncan

duncan what trans do you have ..back in the day the valve bodys on C4 was always dirty ...valves stuck thats why I'd say it was in 3rd ..In the day we used a teflon additive for slickem ...but todays teflon has only 3 drops of teflon in it ..Now you may have other adjustments needed some one else can tell the adjustments that done one since 1968...

 

[feitctaj]

what year is this EB? it may not be an EGR valve , got any photos? it could be a deceleration Valve

 

[blubuckaroo]

Need a photo but it's probably the choke pull-off of an EGR diaphram.

 

[gjrock]

Cruise control?

 

[DirtDonk]

what year is this EB? it may not be an EGR valve , got any photos? it could be a deceleration Valve

I'm with you. That would qualify as a "mysterious" kind of vacuum thingy any day. Didn't see them on too many vehicles so they're not familiar to many.
All the ones I've seen were part steel, with a blue plastic cover (vaguely cone-shaped) on one end and 2 or 3 vacuum nipples coming out at 90° angles.

That sound something like it Duncan? If so, then you only need it if you still have a dual-diaphragm vacuum advance on your distributor. If yours has only one vacuum nipple for advancing timing, then there's no more use for it at this time.
Save it though, just in case you ever get inspected, detected, neglected and rejected, by the smog checkers.

Paul

 

[Duncan]

I'm with you. That would qualify as a "mysterious" kind of vacuum thingy any day. Didn't see them on too many vehicles so they're not familiar to many.
All the ones I've seen were part steel, with a blue plastic cover (vaguely cone-shaped) on one end and 2 or 3 vacuum nipples coming out at 90° angles.

That sound something like it Duncan? If so, then you only need it if you still have a dual-diaphragm vacuum advance on your distributor. If yours has only one vacuum nipple for advancing timing, then there's no more use for it at this time.
Save it though, just in case you ever get inspected, detected, neglected and rejected, by the smog checkers.

Paul

Paul,

I just took a picture of it to show people, but you nailed its description to a "T". I do have a dual-diaphragm vacuum advance on my distributor, except one end was plugged off when I purchased the Bronco. It's a 69' by the way.

Is it okay to plug off one of the vacuums on the distributor, or should I get a new one with single vacuum?

Thanks Paul!

Duncan

 

[oleguy74]

Vacuume

Is This It?came On My 74.

 

[DirtDonk]

I do have a dual-diaphragm vacuum advance on my distributor, except one end was plugged off when I purchased the Bronco. It's a 69' by the way.

Is it okay to plug off one of the vacuums on the distributor, or should I get a new one with single vacuum?

Good question. I'm not sure if there is a difference in advance motion with the dual, as opposed to a single diaphragm advance, but I know people (including me for awhile) who've run the dual-diaphragm with the inner one plugged with no ill effects. If there is a difference, it's probably small and I never noticed any difference in the way mine ran. Other than it had fewer annoying habits during decelleration.
I never did a real comparison using a vacuum pump and timing light though, so don't know if you're losing anything or not.
Either way though, unless your distributor is near-new, it sounds like a good time for a Duraspark upgrade. Or any other modern ignition for that matter.

Paul

 

[72_EB]

Is this this piece you are talking about?
If so, losing it shouldn't make a difference. Old emissions mumbo jumbo.
If you have two ports on your distributor, the front one is advance and the top one is retard. Ignore the retard one (plug it or leave it - doesn't matter), but hook up your advance to the timed port on the passenger side base plate of your stock carb.
Did you change any carb to intake gaskets? There are different sizes. A wrong one will cause a vacuum leak and big lose in power. Spray around your carb base with carb cleaner and check for vacuum leaks. RPMs go up with this, you have a vacuum leak.

 

[72_EB]

Here's an example of an EGR if it looks like this.