Intake vacuum leak
Thread Starter
|
5th Wheeling
Joined: Oct 2022
Posts: 33
Likes: 9
Intake vacuum leak
I'm guessing this has been the vacuum leak I've been fighting. Just bought this 1975 F100 and installed new carb but does'nt run very well and "diesels" when I shut it off. I ordered a new complete gasket kit for the truck as I plan to pull motor after next summer. If my gasket kit does NOT come with this gasket (which I'm certain with my luck it won't. Would high temp silicone work or is there a part # for this? I'm guessing this is called an "intake base plate gasket'?
Hotshot
Joined: Feb 2004
Posts: 10,788
Likes: 2,595
From: The Shenandoah Valley
That'll leak for sure, wrong gasket was used.
No, I would not use silicone.
I'd get a sheet of cardboard like gasket material (not cork) and use my exacto knife and cut me a gasket, then grease both sides of it with a thin smear of axle grease and install it. A dress box from Macy's works.
The grease will seal while not gluing the gasket in place, it will also slightly swell the cardboard which doesn't hurt sealing, and leave it easy to check it's condition next month too when you have your new gasket set. It's under a vacuum, not pressure.
No, I would not use silicone.
I'd get a sheet of cardboard like gasket material (not cork) and use my exacto knife and cut me a gasket, then grease both sides of it with a thin smear of axle grease and install it. A dress box from Macy's works.
The grease will seal while not gluing the gasket in place, it will also slightly swell the cardboard which doesn't hurt sealing, and leave it easy to check it's condition next month too when you have your new gasket set. It's under a vacuum, not pressure.
Lead Driver
Joined: Nov 2006
Posts: 5,217
Likes: 506
From: Pa.
It appears there is coolant leaking from the square bore carb spacer also. The dampness in the intake looks to be coolant which will make it impossible to get it to idle properly. Does your new carb have a provision for your PCV valve to? If so eliminate the oem base plate and replace with a phenolic spacer. They come in various thicknesses. I would start with a thickness that's equal to your current base plate so not to complicate how your throttle linkage mates up.
Lead Driver
Joined: Nov 2006
Posts: 5,217
Likes: 506
From: Pa.
One common problem with ford intakes is the exhaust crossover, in some versions, is that enough heat in the right conditions is radiated from the intake to the bowls on the carb that it will boil ethanol fuel quite readily. To prevent that a phenolic spacer is used to provide a thermal break preventing "heat soak". The spacer you have is from the mid 60's and will always be a problem finding the right replacement gasket.
Thread Starter
|
5th Wheeling
Joined: Oct 2022
Posts: 33
Likes: 9
That explains it One common problem with ford intakes is the exhaust crossover, in some versions, is that enough heat in the right conditions is radiated from the intake to the bowls on the carb that it will boil ethanol fuel quite readily. To prevent that a phenolic spacer is used to provide a thermal break preventing "heat soak". The spacer you have is from the mid 60's and will always be a problem finding the right replacement gasket.
One common problem with ford intakes is the exhaust crossover, in some versions, is that enough heat in the right conditions is radiated from the intake to the bowls on the carb that it will boil ethanol fuel quite readily. To prevent that a phenolic spacer is used to provide a thermal break preventing "heat soak". The spacer you have is from the mid 60's and will always be a problem finding the right replacement gasket.
Lead Driver
Joined: Nov 2006
Posts: 5,217
Likes: 506
From: Pa.
The coolant passages on your current spacer can be easily be eliminated by capping off the plumbing at the source as long as you have an adequate choke set up. I would run the 1" phenolic spacer you have on top of the intake with the proper gaskets. Once you have it half-way running check for vacuum leaks again using a spray can of your choice WD-40 or brake clean etc. lightly spraying the suspected leak area noting if an increase in rpm of your motor happens. There's where your vacuum leak will be.
Trending Topics
Logistics Pro
Joined: Oct 2006
Posts: 4,029
Likes: 891
From: East Central Ia
Early, maybe up to egr years 429's/460/s had the phenolic spacer plate with pcv built in. https://th.bing.com/th/id/OIP.qCL09D...id=ImgDet&rs=1. Just to give you an idea.
FTE Stories
Ford Trucks for Ford Truck Enthusiasts
2027 Ford Super Duty Buyer's Guide (Every Model, Engine, & Package)
Brett Foote
Top 10 Ford Truck Tragedies
Joe Kucinski
AEV FXL Super Duty - the Super Duty Raptor Ford Doesn't Make
Brett Foote
Lobo Vs Lobo: Proof the F-150 Lobo Should Be Even Lower!
Michael S. Palmer
Ford's 2001 Explorer Sportsman Concept Looks For a New Home
Verdad Gallardo
10 Best Ford Truck Engines We Miss the Most!
Joe Kucinski
2026 Shelby F-150 Off-Road: Better Than a Raptor R?
Brett Foote
2027 Super Duty Carhartt Package First Look: 12 Things You NEED to Know!
Michael S. Palmer
10 Most Surprising 2026 Ford Truck Features!
Joe Kucinski
FTE Legend
Joined: Nov 2015
Posts: 30,898
Likes: 4,120
From: Angier, NC
To hot a plug and carbon build up is also a cause but most of the time idle speed to high.
If you have an auto trans shut it off in gear then when off put in park.
Dave ----
Thread Starter
|
5th Wheeling
Joined: Oct 2022
Posts: 33
Likes: 9
That spacer is pre-egr valve. The egr valve was mandated in the early 70's. Your PCV valve should be connected to it. Your carb where you have your power brake booster connected is usually connected to the vacuum tree mounted in the back of the intake manifold. Your PVC valve connects to that spot on your carb. Also they make phenolic spacers with the PCV plumbing provision.
The coolant passages on your current spacer can be easily be eliminated by capping off the plumbing at the source as long as you have an adequate choke set up. I would run the 1" phenolic spacer you have on top of the intake with the proper gaskets. Once you have it half-way running check for vacuum leaks again using a spray can of your choice WD-40 or brake clean etc. lightly spraying the suspected leak area noting if an increase in rpm of your motor happens. There's where your vacuum leak will be.
The coolant passages on your current spacer can be easily be eliminated by capping off the plumbing at the source as long as you have an adequate choke set up. I would run the 1" phenolic spacer you have on top of the intake with the proper gaskets. Once you have it half-way running check for vacuum leaks again using a spray can of your choice WD-40 or brake clean etc. lightly spraying the suspected leak area noting if an increase in rpm of your motor happens. There's where your vacuum leak will be.
I feel like my vacuum advance isn't pulling enough vacuum from carb port. It pulls lots on bottom front port of carb,, but not near enough on the side port. Truck is timed at 10* with vacuum plugged,, but cant get anymore once the vacuum advance line is attached. (i DO have a new distributor coming)
This is all a Duraspark system
Lead Driver
Joined: Nov 2006
Posts: 5,217
Likes: 506
From: Pa.
I already have the 1" phenolic spacer. I'm thinking of removing that stock EGR spacer and just run the phenolic spacer, problem is it doesnt have the PCV port on it. Is it possible to run the PVC line to the air breather (like it is on the drivers side) or an "intake tree"? Or run to back of carburator and move my brake booster? I could go buy the 1" phenolic with the PVC port, but then I'm in the same scenario.
I feel like my vacuum advance isn't pulling enough vacuum from carb port. It pulls lots on bottom front port of carb,, but not near enough on the side port. Truck is timed at 10* with vacuum plugged,, but cant get anymore once the vacuum advance line is attached. (i DO have a new distributor coming)
This is all a Duraspark system
I feel like my vacuum advance isn't pulling enough vacuum from carb port. It pulls lots on bottom front port of carb,, but not near enough on the side port. Truck is timed at 10* with vacuum plugged,, but cant get anymore once the vacuum advance line is attached. (i DO have a new distributor coming)
This is all a Duraspark system
If you take a pic of your intake behind carb we can ID a spot for the power brake booster vacuum connection. No need to buy another phenolic spacer with the PVC provision. I think you can safely eliminate the aluminum oem carb spacer and come up with a workable solution.
Logistics Pro
Joined: Oct 2006
Posts: 4,029
Likes: 891
From: East Central Ia
Ported vacuum from side of carb doesn't have any vacuum until throttle is opened, that's normal. I didn't see an egr port in manifold picture. I don't ever remember a water heated egr spacer plate. PCV should normally be in carb base and booster on a vacuum tree. I don't remember a water heated carb spacer much later than mid 60's. Anything's possible and memory getting fuzzy.
Thread
Thread Starter
Forum
Replies
Last Post
cgunning17
1980 - 1986 Bullnose F100, F150 & Larger F-Series Trucks
10
Sep 7, 2018 07:56 AM
benbuilder
1973 - 1979 F-100 & Larger F-Series Trucks
8
Jun 13, 2016 07:18 PM
ironhead86
1973 - 1979 F-100 & Larger F-Series Trucks
2
Apr 9, 2009 06:39 PM