Vacuum Line at Carb Question (2 Viewers)

[PabloCruise]

If anyone needs a diagram or reference let me know, but I'm swamped at work and can't do a full scan at the moment. I have a 1978 2f emission control repair manual (pub #98270) that I got from SOR way back when.

If you have the capability to do a full scan of the '78 manual, that sounds awesome!

 

[PabloCruise]

My original question that started this thread was, "What does this port at the top, front of my carb connect to?"

I think it is safe to say it goes through the HIC and then routes to the smaller, forward manifold vacuum port located in the carb insulator.

Can anyone tell me what this port on the top, front of the carb is for?
Is it to the Power Valve? Or something else?
I am not finding a surplus of information on this...

 

[Fast Eddy]

I think that is the power valve. @65swb45 knows for sure.

 

[PabloCruise]

I think that is the power valve. @65swb45 knows for sure.

Thanks man!

I am getting ready to refresh all my vacuum lines, so I want to make sure I am understanding what is going on with all the circuits.

 

[PabloCruise]

Attached is a PDF of the 1981 2F Emission Control Repair Manual, if it's of use to anyone.

Nice!
Thank you for sharing.

 

[65swb45]

My original question that started this thread was, "What does this port at the top, front of my carb connect to?"

I think it is safe to say it goes through the HIC and then routes to the smaller, forward manifold vacuum port located in the carb insulator.

Can anyone tell me what this port on the top, front of the carb is for?
Is it to the Power Valve? Or something else?
I am not finding a surplus of information on this...

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That’s a bowl vent. The little domed plug above it covers the access to the power piston.

 

[PabloCruise]

That’s a bowl vent. The little domed plug above it covers the access to the power piston.

Thanks for replying Mark!
I thought this was the bowl vent - routes back to the charcoal canister via the Outer Vent Control Valve?

 

[Pin_Head]

My original question that started this thread was, "What does this port at the top, front of my carb connect to?"

I think it is safe to sa y it goes through the HIC and then routes to the smaller, forward manifold vacuum port located in the carb insulator.

Can anyone tell me what this port on the top, front of the carb is for?
Is it to the Power Valve?

I just went out and looked at a ‘78 top cover and indeed, it is a separate bowl vent in addition to the large tube that runs to the charcoal canister. In addition, this little port at the front of the top goes straight in to the air horn for the secondary. Seems strange. I wonder where the hose for this goes and what it does. It doesn’t seem likely that its primary function is to vent the bowl.

 

[fjc-man]

I’m thinking this orifice on the 78 carb top is really serving a similar purpose to the red hose connecting the hot idle compensator on my 79 to a manifold vacuum source below the carb. A supply of filtered air.

 

[PabloCruise]

Edit: Ah. Late to the party. "Thermostatic Valve" seems to be it. Still not mentioned by name.

That little guy shows up in the emissions manual, but I don't see where it's ever given a name and it doesn't have it's own test procedure like all the other components. 2 ports for CA, TP and EGR run from the carb base ports through this. For federal there's one more port for the spark arrestor which goes to the advancer port at the carb base.

I was going through my emissions manual yesterday and still don't see them give the HIC any discussion. What year manual are you see this?

 

[PabloCruise]

Thanks for chiming in Ed. I have no idea where my manuals are right now. I haven’t seen them since the warehouse fire when I moved my office, and I don’t feel like spitballing.

Any chance you can scan those?

I will add though that my memory was correct about the little red hose with the 180. I had to move something on my carburetor workbench yesterday and I found one of those thermostatic boxes leftover from a desmog. It still had the U shaped red hose that went up to the top of the carb.

Mark, I have the Emissions Manual for '78, it covers Fed/Cali/High-Altitude. I grabbed a few scans for the Fed spec systems. They aren't great, I just have a basic desk top scanner, but I will post them up later today.

 

[PabloCruise]

If anyone needs a diagram or reference let me know, but I'm swamped at work and can't do a full scan at the moment. I have a 1978 2f emission control repair manual (pub #98270) that I got from SOR way back when.

You might be able to get better looking scans than I at your work. Or you might be able to scan the entire manual as a PDF. I just grabbed the high-level Fed Spec systems as images. I want to do some mark up on a few for my own keeping track of things...

 

[PabloCruise]

I just went out and looked at a ‘78 top cover and indeed, it is a separate bowl vent in addition to the large tube that runs to the charcoal canister. In addition, this little port at the front of the top goes straight in to the air horn for the secondary. Seems strange. I wonder where the hose for this goes and what it does. It doesn’t seem likely that its primary function is to vent the bowl.

Thanks Charlie! I appreciate you looking. I think it is funny that as much tech as we have going here on MUD, I did not find much/any info on this port and how it connects.

Did you mean to post a picture with your message? The part in bold doesn't make much sense to me w/o an image.

When you ask where the hose for this goes, I thought we had been establishing so far that this port connects to to the HIC at the ports I circled above, and then down to manifold vacuum at the carb insulator? Tell me if I am wrong on this. I had my 40 in for some work and they had the manifolds off. When I got it back this line was disconnected and I am having a hard time figuring out the correct connecting for this vacuum line!

If this is some form of bowl vent, and not a vacuum connection to the power valve, then I guess there is little in the way of power or performance that will be affected by the missing connection.

 

[Pin_Head]

I didn’t take a picture, but to paint an image of what is going on with the front facing brass vacuum tube in the top cover, it is drilled straight through so if you put a piece of wire in the tube, it will go straight in and come out inside the secondary air horn or bore. It also takes a 90 turn down and connects to the fuel bowl.

It is not for the HIC. The HIC gets air from the air cleaner, goes down to the box that has the reed switch and then goes to the insulator base, where it bleeds air in to the manifold when the carb is hot and idling.

 

[PabloCruise]

I didn’t take a picture, but to paint an image of what is going on with the front facing brass vacuum tube in the top cover, it is drilled straight through so if you put a piece of wire in the tube, it will go straight in and come out inside the secondary air horn or bore. It also takes a 90 turn down and connects to the fuel bowl.

It is not for the HIC. The HIC gets air from the air cleaner, goes down to the box that has the reed switch and then goes to the insulator base, where it bleeds air in to the manifold when the carb is hot and idling.

Hmm...

Is it the port I have circled in red in this picture?

Or are you saying there is another port on yours - not pictured here?

 

[PabloCruise]

I just went out and looked at a ‘78 top cover and indeed, it is a separate bowl vent in addition to the large tube that runs to the charcoal canister. In addition, this little port at the front of the top goes straight in to the air horn for the secondary. Seems strange. I wonder where the hose for this goes and what it does. It doesn’t seem likely that its primary function is to vent the bowl.

Re-reading your post reminded me of this image, I was amazed I could find it again. I think based on the 2 vacuum lines at the junction block, and your description, you have a High Altitude spec carb in your possession. I am going to attach a scan from my manual for the HA Layout - tell me if you agree.

The above pic is from this thread: VSV part for 78 FJ40 - https://forum.ih8mud.com/threads/vsv-part-for-78-fj40.226005/page-2#post-3449470

High Altitude Layout from the 1978 2F Emissions Manual - note the extra line just below the air cleaner. It connects to the HAC (High Altitude Compensation) valve:

 

[Pin_Head]

No. I don’t have the HAC model. There is just one brass tube with the number8 by it. The second photo shows the connection to the bowl.

 

[PabloCruise]

No. I don’t have the HAC model. There is just one brass tube with the number8 by it. The second photo shows the connection to the bowl.

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Got it.

Those pictures are awesome! That pretty well establishes the bowl vent function of that port - I wonder why they didn't just run that bowl vent to the air horn?
Gratitude for taking the time to take pictures and post!!!

So it looks like you have a late April, 1978, non-HA carb.

 

[PabloCruise]

The Emission Control Repair Manual is pretty awesome.

I learned about the HA spec system when I scanned the above. While I was flipping through the manual for the HAC system, I found mention of the Power Valve system - complete w/ an external vacuum port - for Cali spec carbs.

So I thought I would try to get some useful scans from the manual for the various systems. Unless I state otherwise, these scans are all for Fed spec.

Toyota US pub no: 98270

 

[PabloCruise]

1978 2F Emission Control Repair Manual Table of Contents for Chapter 4 (where they show all the systems):