guidance needed PCV and Power Brake vaccuum hoses

[rockinreel]

1984 AMC 360, 15K on bottom, 1500 on top, but it
1. smokes out exhaust on hot idle after running several miles.
2. Occasionally, carb stumbles in 3rd or 4th gear, after hot idle when driving.

Found that the shop that installed my engine has the PCV hooked to the power brake inlet on carb.

Need help on:
1. When I route the PCV hose from the back of carb to the front of the carb, I block off the power brake inlet on the carb, but what do I do with the hose left in the front of the manifold that was hooked to the carb's PCV inlet.

2. Could that issue cause the smoke issue when revving at hot idle?
(Have Edelbrok intake and offroad carb #1825 if pics don't' show)

 

[hagar]

The PCV hose routing looks okay to me.

The brake booster needs it's own dedicated vacuum source. Ideally you don't want anything else plumbed into that hose.
So find a dedicated connection to manifold vacuum on the manifold; maybe you'll have to remove a plug somewhere to do that. The closer to the bosster unit the better.
That's my opinion.

 

[mtnwhlr]

The way it is hooked up is fine. Vac at the base of the carb is the same front to back and it is not the problem with it smoking.

 

[rockinreel]

I hooked the PCV to the PCV inlet in the front of the carb like the manual says (even if it doesn't matter). Jeep idles fine.

So I have this Power Brake Port inlet on the carb that is sucking in air loudly. Directions say "IF NOT IN USE, MUST BE PLUGGED WITH 1/4 NPT PIPE PLUG".

What or where would a Power Brake port connect to from the carb?

 

[Torxhead]

You are going to have to get a 1/4" npt nipple with the correct hose size for the power brake and use that.

 

[rockinreel]

Torxhead,
I'm less experienced than you think I am (and that I think I am). I do have an extra 90* threaded pipe port (plugged) on my manifold that I can run a hose to the Power Brake Port of the carb.

AND.... I will spend time when I get home to figure out where this power brake booster thingy can have a hose plugged into it

 

[007]

Torxhead,
I'm less experienced than you think I am (and that I think I am). I do have an extra 90* threaded pipe port (plugged) on my manifold that I can run a hose to the Power Brake Port of the carb.

AND.... I will spend time when I get home to figure out where this power brake booster thingy can have a hose plugged into it

Regardless of which one you use - make sure it A) doesn't go anywhere else but the booster, and B) that you plug the rest of the vac ports if not in use.

With that...you should be good to go.

 

[Woolyworm]

You should try and run brake boost vac off the middle of the intake and typical at the base of the carb.

You don't want it in only one of the intake rails since it draws a lot of vac and can cause valve burn issues if directed to just one rail - that's what I've read and been told anyway.


Wooly

 

[007]

You should try and run brake boost vac off the middle of the intake and typical at the base of the carb.

You don't want it in only one of the intake rails since it draws a lot of vac and can cause valve burn issues if directed to just one rail - that's what I've read and been told anyway.


Wooly

Not arguing whatsoever, just curious / skeptical. I can't see how that's possible... A net loss of vacuum is a net loss of vacuum isn't it? Two lines running to one running to the booster is the same use of available vacuum.

 

[mriplaybass]

Not arguing whatsoever, just curious / skeptical. I can't see how that's possible... A net loss of vacuum is a net loss of vacuum isn't it? Two lines running to one running to the booster is the same use of available vacuum.

I can't claim to be any kind of authority on this matter since I have had the same thought process myself. However, I know in water systems, and probably any kind of fluid or gas transfer, the longer the run of hose, pipe, etc., the larger the pipe has to be in order to get the desired flow at the point of delivery due to friction within the pipe, hose, etc.. Think of it this way. Why don't we use 1/4" air hose to power all air tools? Sure would be easier to haul around a 1/4" hose instead of for example, the huge hose that pneumatic jack hammers use. If you measure the pressure at the end of a 1/4" hose and a 1" hose hooked up to a 120psi compressor tank, the pressure will be 120psi, but the 2 hoses can't do the same work.
Similarly, IMHO, I would assume that within an intake manifold, the pressure, or in this case lowered pressure, ie, vacuum, can have fluctuations depending on where in the manifold you connect the vacuum. Putting a "T" in a vacuum line to facilitate an additional line would, using the above principals, affect the vacuum going to whatever is tapped into the original line. Hope this makes things a bit more understandable.

 

[Woolyworm]

Vacuum at the carb base is split pretty evenly by all intake runners. Vacuum on the runner is only from that runner. The PCV and booster should be getting constant vacuum - hooking either to only one runner does not provide good, constant vacuum. It will also create s lean condition in the associated cylinder and burn the valves/piston up.

Both the booster and pcv are heavy users and should hook up to the correct port on the carb, a central port on the intake, or a port on the carb plate.

Cheers

http://performanceunlimited.com/cobravalley_drivetrain/howtoplumbpcvsystem.html


Wooly

 

[007]

Okay - I can buy most of that I think. I do know that you CAN have too much vacuum to your booster, but that's rare.

 

[rockinreel]

Vacuum at the carb base is split pretty evenly by all intake runners. Vacuum on the runner is only from that runner. The PCV and booster should be getting constant vacuum - hooking either to only one runner does not provide good, constant vacuum. It will also create s lean condition in the associated cylinder and burn the valves/piston up.

Both the booster and pcv are heavy users and should hook up to the correct port on the carb, a central port on the intake, or a port on the carb plate.

Cheers

Cobra Valley's HOW TO PLUMB Positive Crankcase Ventilation Systems


Wooly

Thanks a million, I'm WAY more educated on this "issue". Though I've discovered that I do not have a brake booster, unless it's hidden inside the firewall way up under the dash. So, I plugged (blocked) the brake booster port on the carb, as Edelbrock says to do. So, with my PCV to carb being good to go, should I:

1. Leave the carb brake booster port plugged? (sounds like a jet engine not plugged and idles erratic)
2. Plug carb brake booster inlet into the second intake vacuum source in the middle of the intake? (currently plugged, (is a threaded pipe))

thanks

 

[007]

If it's not used PLUG THEM. ;-)


Sent from my iPhone using Tapatalk

 

[Woolyworm]

Correct. Plug/cap all unused vac ports.


Wooly