Vacuum Line at Carb Question (2 Viewers)

[PabloCruise]

I searched, yes, I searched. Before that I looked all through my Emissions Manual.

1978 (Sep '77 build date) Fed Spec 40.

I had someone else under the hood for some work (film at 11) and they left a few vacuum lines disconnected.

My question - where does this port - see blue arrow - connect? I remember having to track this down probably ~20 years ago, but I don't know where I found my answer.

And why isn't this shown in the Emissions Manual for '78???

Thanks All!

 

[65swb45]

I searched, yes, I searched. Before that I looked all through my Emissions Manual.

1978 (Sep '77 build date) Fed Spec 40.

I had someone else under the hood for some work (film at 11) and they left a few vacuum lines disconnected.

My question - where does this port - see blue arrow - connect? I remember having to track this down probably ~20 years ago, but I don't know where I found my answer.

And why isn't this shown in the Emissions Manual for '78???

Thanks All!

View attachment 3545445

Iirc it comes up from the insulator.

 

[PabloCruise]

Iirc it comes up from the insulator.

Ah, that sounds about right!

There are 2 ports on the insulator for 1978, yes? Maybe the other goes to the VCV for evap?

Again, why is this not in the emissions manual?!?

Thanks Mark

 

[PabloCruise]

Iirc it comes up from the insulator.

Do you know what this port does? Routing manifold vacuum to the top of the carb?

 

[65swb45]

Do you know what this port does? Routing manifold vacuum to the top of the carb?

Not from memory. But I am virtually certain that it IS covered in the manual.

 

[PabloCruise]

Not from memory. But I am virtually certain that it IS covered in the manual.

I would not question you on that, but I did take a detailed pass through the Emissions Manual for '78.

I do NOT have a carb manual, maybe it is covered in there?

 

[Pin_Head]

Even if I once knew, I have forgotten because I don’t know. It is a larger inside diameter than the other lines that are for vacuum control, so I suspect that it maybe for some kind of vent line. It is not the bowl vent so maybe it provides filtered air from the air cleaner to the VSV or hot idle compensator? Just spitballing.

 

[65swb45]

I seem to remember a short red hose that made a 180 from the box to the bowl vent. It would make sense to put the box inline between the bowl vent and the manifold vacuum source as a restrictor to prevent a vacuum leak while providing bowl venting since that model did not have the charcoal canister sized line coming out the side of the air horn.

 

[PabloCruise]

I seem to remember a short red hose that made a 180 from the box to the bowl vent. It would make sense to put the box inline between the bowl vent and the manifold vacuum source as a restrictor to prevent a vacuum leak while providing bowl venting since that model did not have the charcoal canister sized line coming out the side of the air horn.

I believe this build: '78 Fed Spec does vent the bowl to a switched valve (Outer Vent Control Valve) on the charcoal cannister.
I will visually verify on my actual 40, but here is this:

 

[fjc-man]

5/79 one hose to the air cleaner and the one off the bottom goes to a pipe on the carb insulator. @FJ40Jim, can you tell us the function of the doohickey with the red hose attached to the air cleaner? It’s not covered in the 79 emissions manual. Thanks, Bill

 

[PabloCruise]

I believe this build: '78 Fed Spec does vent the bowl to a switched valve (Outer Vent Control Valve) on the charcoal cannister.
I will visually verify on my actual 40, but here is this:
View attachment 3546145

Confirmed - my bowl vent runs as shown to the outer vent control valve on the charcoal cannister.

 

[PabloCruise]

5/79 one hose to the air cleaner and the one off the bottom goes to a pipe on the carb insulator.View attachment 3546249View attachment 3546250

Thank you so much! I think '79 model year is quite a bit different than '78.

 

[PabloCruise]

Iirc it comes up from the insulator.

For the purposes of clarity - you are saying it connects to manifold vacuum under the carb?
This looks like it could be an option - there are 2 ports, one is connected to the VCV to purge the charcoal canister.

 

[fjc-man]

I have a 79 emissions manual and there is no mention of this doohickey. It appears to be a controlled vacuum leak at higher temperatures, I warmed it up with a heat gun and that’s when it opened to the air cleaner. There is a bimetallic spring acting on that plunger.

 

[PabloCruise]

I have a 79 emissions manual and there is no mention of this doohickey. It appears to be a controlled vacuum leak at higher temperatures, I warmed it up with a heat gun and that’s when it opened to the air cleaner. There is a bimetallic spring acting on that plunger.View attachment 3546816View attachment 3546817

Interesting.
Some kind of thermal control of some sort.
I am figuring out that the Emissions Manual is not a comprehensive resource for all the vacuum lines connected to our carbs.

 

[PabloCruise]

Alright, my need to know is kicking in here.

I am wondering if this might be a port to my power valve?

@Pin_Head refers to the Port 8 as "external control for the power valve" in this post: (Note: the carb in this thread is not a '78)

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[PabloCruise]

Here are pics from my rig - 9/77 build 40. I believe it to be a 1978 Fed Spec.

 

[PabloCruise]

When I go to the 2F Engine Repair Manual, Fuel System, Carburetor section, I see this schematic for non-US. It looks like the power valve (17) is routed to manifold vacuum?

 

[PabloCruise]

Same section, same manual, US carb circuits - for power valve (18), they conveniently omit showing how the power valve connects:

 

[fjc-man]

What does that 7H30 date code on your carb translate to, or is that how you determined it is 78 model year? I think your doohickey is the same as a 79 except yours is drawing filtered air from that port rather than from the air cleaner.