Poor carb to manifold match
11-13-2017, 03:25 PM
#1
Instructor
Thread Starter
Poor carb to manifold match
After struggling since I bought my car to get it to run properly I decided to bite the bullet and buy a new carb, went for a Holley Brawler 670cfm.
The fit was fairly straightforward with a couple of modifications like fitting an ebow in the vacuum tapping for the vacuum operated stuff, a new fuel inlet to join up to the dual fuel inlets and a bit of modification of the throttle cable.
First start was a bit of a shock when it revved straight to about 4500revs but a quick blip of the throttle brought it down to a reasonable fast idle, I let it run until the choke came off and for the first time I had a smooth idle at about 750revs so that's a result straight away!
With winter weather taking over I haven't had it out on the road yet but it has to be better than it was.
Anyway the car came to me with a Performer inlet and a 600cfm Holley List 6619-1 which bolted to the manifold which is drilled for spread bore and square bore carbs, what I hadn't noticed was where the vacuum connection for the engine breather comes of the carb body there is a gap in the mounting face which creates a leak between the carb and the manifold resulting in a loss of vacuum making it impossible to get an idle.
It was only when I took the carb off the gap in the marking on the gasket was clear so with some combinations it's not a case of one size fits all.
If I'd spotted it before on the numerous times I had the carb off I could have maybe fitted a thin plate between the carb and manifold(hood clearance is tight) but hey I've got a nice shiny new carb on my engine now!
Graham
The fit was fairly straightforward with a couple of modifications like fitting an ebow in the vacuum tapping for the vacuum operated stuff, a new fuel inlet to join up to the dual fuel inlets and a bit of modification of the throttle cable.
First start was a bit of a shock when it revved straight to about 4500revs but a quick blip of the throttle brought it down to a reasonable fast idle, I let it run until the choke came off and for the first time I had a smooth idle at about 750revs so that's a result straight away!
With winter weather taking over I haven't had it out on the road yet but it has to be better than it was.
Anyway the car came to me with a Performer inlet and a 600cfm Holley List 6619-1 which bolted to the manifold which is drilled for spread bore and square bore carbs, what I hadn't noticed was where the vacuum connection for the engine breather comes of the carb body there is a gap in the mounting face which creates a leak between the carb and the manifold resulting in a loss of vacuum making it impossible to get an idle.
It was only when I took the carb off the gap in the marking on the gasket was clear so with some combinations it's not a case of one size fits all.
If I'd spotted it before on the numerous times I had the carb off I could have maybe fitted a thin plate between the carb and manifold(hood clearance is tight) but hey I've got a nice shiny new carb on my engine now!
Graham
11-13-2017, 05:15 PM
#2
After struggling since I bought my car to get it to run properly I decided to bite the bullet and buy a new carb, went for a Holley Brawler 670cfm.
The fit was fairly straightforward with a couple of modifications like fitting an ebow in the vacuum tapping for the vacuum operated stuff, a new fuel inlet to join up to the dual fuel inlets and a bit of modification of the throttle cable.
First start was a bit of a shock when it revved straight to about 4500revs but a quick blip of the throttle brought it down to a reasonable fast idle, I let it run until the choke came off and for the first time I had a smooth idle at about 750revs so that's a result straight away!
With winter weather taking over I haven't had it out on the road yet but it has to be better than it was.
Anyway the car came to me with a Performer inlet and a 600cfm Holley List 6619-1 which bolted to the manifold which is drilled for spread bore and square bore carbs, what I hadn't noticed was where the vacuum connection for the engine breather comes of the carb body there is a gap in the mounting face which creates a leak between the carb and the manifold resulting in a loss of vacuum making it impossible to get an idle.
It was only when I took the carb off the gap in the marking on the gasket was clear so with some combinations it's not a case of one size fits all.
If I'd spotted it before on the numerous times I had the carb off I could have maybe fitted a thin plate between the carb and manifold(hood clearance is tight) but hey I've got a nice shiny new carb on my engine now!
Graham
The fit was fairly straightforward with a couple of modifications like fitting an ebow in the vacuum tapping for the vacuum operated stuff, a new fuel inlet to join up to the dual fuel inlets and a bit of modification of the throttle cable.
First start was a bit of a shock when it revved straight to about 4500revs but a quick blip of the throttle brought it down to a reasonable fast idle, I let it run until the choke came off and for the first time I had a smooth idle at about 750revs so that's a result straight away!
With winter weather taking over I haven't had it out on the road yet but it has to be better than it was.
Anyway the car came to me with a Performer inlet and a 600cfm Holley List 6619-1 which bolted to the manifold which is drilled for spread bore and square bore carbs, what I hadn't noticed was where the vacuum connection for the engine breather comes of the carb body there is a gap in the mounting face which creates a leak between the carb and the manifold resulting in a loss of vacuum making it impossible to get an idle.
It was only when I took the carb off the gap in the marking on the gasket was clear so with some combinations it's not a case of one size fits all.
If I'd spotted it before on the numerous times I had the carb off I could have maybe fitted a thin plate between the carb and manifold(hood clearance is tight) but hey I've got a nice shiny new carb on my engine now!
Graham
If your intake manifold was made for a spread bore you have to use an aluminum adapter to use a square bore and vice versa because of a giant vacuum leak. The manifold has 8 tapped holes in it so you can bolt the aluminum adapter on and then bolt the carburetor to the adapter. Here's what the aluminum adapter looks like: https://www.ebay.com/itm/1932-Carbur...4d:g:V7kAAOSwZ
Last edited by NeverTooOld; 11-13-2017 at 05:17 PM.
11-13-2017, 05:52 PM
#3
Race Director
got a pic of the mounting face? just cuz it is drilled for both sets of bolts doesn't mean there isn't a mismatch that could cause the throttle plates to hit on the manifold flange. and the correct adaptor is about 3/4 inch thick. put the air cleaner on. loosely wad up some aluminum foil. set it on the top of air filter. close hood. like playdoh it'll show you how much more room you do or don't have.
Last edited by derekderek; 11-13-2017 at 05:54 PM.
11-13-2017, 06:08 PM
#4
Race Director
After struggling since I bought my car to get it to run properly I decided to bite the bullet and buy a new carb, went for a Holley Brawler 670cfm.
The fit was fairly straightforward with a couple of modifications like fitting an ebow in the vacuum tapping for the vacuum operated stuff, a new fuel inlet to join up to the dual fuel inlets and a bit of modification of the throttle cable.
First start was a bit of a shock when it revved straight to about 4500revs but a quick blip of the throttle brought it down to a reasonable fast idle, I let it run until the choke came off and for the first time I had a smooth idle at about 750revs so that's a result straight away!
With winter weather taking over I haven't had it out on the road yet but it has to be better than it was.
The fit was fairly straightforward with a couple of modifications like fitting an ebow in the vacuum tapping for the vacuum operated stuff, a new fuel inlet to join up to the dual fuel inlets and a bit of modification of the throttle cable.
First start was a bit of a shock when it revved straight to about 4500revs but a quick blip of the throttle brought it down to a reasonable fast idle, I let it run until the choke came off and for the first time I had a smooth idle at about 750revs so that's a result straight away!
With winter weather taking over I haven't had it out on the road yet but it has to be better than it was.
Anyway the car came to me with a Performer inlet and a 600cfm Holley List 6619-1 which bolted to the manifold which is drilled for spread bore and square bore carbs, what I hadn't noticed was where the vacuum connection for the engine breather comes of the carb body there is a gap in the mounting face which creates a leak between the carb and the manifold resulting in a loss of vacuum making it impossible to get an idle.
It was only when I took the carb off the gap in the marking on the gasket was clear so with some combinations it's not a case of one size fits all.
If I'd spotted it before on the numerous times I had the carb off I could have maybe fitted a thin plate between the carb and manifold(hood clearance is tight) but hey I've got a nice shiny new carb on my engine now!
Graham
It was only when I took the carb off the gap in the marking on the gasket was clear so with some combinations it's not a case of one size fits all.
If I'd spotted it before on the numerous times I had the carb off I could have maybe fitted a thin plate between the carb and manifold(hood clearance is tight) but hey I've got a nice shiny new carb on my engine now!
Graham
DUB
11-19-2017, 03:58 PM
#5
Instructor
Thread Starter
Not asking a question just sharing my experience to hopefuly assist others, sorry if I didn't make that clear, this problem had me chasing down dead ends for a long time before I discovered the real cause of my problems, I did find lots of other issues along the way like about 3/16" of end play on my distributor shaft! but the main issue was the vacuum leak.
Graham
Graham
11-19-2017, 05:13 PM
#6
Le Mans Master
Member Since: Aug 2017
Location: Cool Northern Michigan
Posts: 6,904
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If your intake manifold was made for a spread bore you have to use an aluminum adapter to use a square bore and vice versa because of a giant vacuum leak. The manifold has 8 tapped holes in it so you can bolt the aluminum adapter on and then bolt the carburetor to the adapter. Here's what the aluminum adapter looks like: https://www.ebay.com/itm/1932-Carbur...4d:g:V7kAAOSwZ
Last edited by HeadsU.P.; 11-19-2017 at 05:14 PM.
11-19-2017, 05:19 PM
#7
Race Director
Not asking a question just sharing my experience to hopefuly assist others, sorry if I didn't make that clear, this problem had me chasing down dead ends for a long time before I discovered the real cause of my problems, I did find lots of other issues along the way like about 3/16" of end play on my distributor shaft! but the main issue was the vacuum leak.
Graham
Graham
Good to pass along what we encounter to hopefully help others.
DUB