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I have a relatively new Edlebrock 1406 on a stock manifold with a 1973 351 4V. The car is believed to have a non stock cam although I do not have the numbers. Mild at best.

New fuel pump. ignition conversion. No more points.

The problem I have seems to be very common. The car starts great when cold and will start again perfectly a few minutes later once shut off. Idle is fine and performance seems appropriate.

However, summer and winter once it has been run for a 1/2 hour lets say and parked for more than 15 minutes it is pretty tough to get to crank over - although it always does. One day I assume I will kill a battery.

I've experimented with carb settings, (with my limited abilities) and different throttle positions when cranking. From what I read this is likely a fuel boiling or draining issue and is somewhat "normal" with this carb. A spacer in this case hasn't helped and this happened with both the old 1406 and a newer one. The fuel filter is near the manifold so maybe I could try and isolate that better if the fuel is being boiled out of there.

My question is would for example a Holley 750cfm be less prone to this issue or am I just spending money for no reason? Can I improve the 1406 or just give it up and make a switch and get better starting and performance? If so, is the Holley more difficult to dial in?

I feel like the Edlebrock is a simple carb (perfect for me) but that might also be limiting in terms of its performance in this case. I know there are some Edlebrock carb haters here and this may be why!

 

I also have some of the stock parts to convert the car back to the original carb. set up. Would this be a waste of effort in terms of reliability and performance and more aggravation - with the only benefit being it is now correct (which I like but it is not vital)?

Thanks for your help.

Jeff

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Next time you try to start it under those conditions put the accelerator pedal to the floor while you crank on it, when it starts let off the gas and you should be good to go. The problem you are having is fuel perculation, if you have enough hood clearance a phenolic carb spacer will help resolve this issue.

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.

the word 'tough" is meaningless.

 

does it turn over more slowly when the engine is up to operating temp.

 

if it does, remove the coil wire the next time it does that and tell us what it does.

 

it may be that your starter is either heat soaking, or your timing is too far advanced. or your fuel level in the carb is too high.

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Cranking just fine when warm. Not more slowly. Soubds strong. Just won't catch without multiple attempts and various machinations with the gas pedal.


Next time you try to start it under those conditions put the accelerator pedal to the floor while you crank on it, when it starts let off the gas and you should be good to go. The problem you are having is fuel perculation, if you have enough hood clearance a phenolic carb spacer will help resolve this issue.

 

Yup. Sometimes that does it.

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Because you've already tried a spacer (assuming it's not metal) you shouldn't be getting fuel bowl percolation, especially in the winter. If the fuel line between the fuel pump and carburetor is too close to, or touching, the engine, fuel could be percolating in the line and causing a flooding problem. I have seen carburetors with porous castings that allow fuel to drain into the intake manifold. Sometime after you have been driving long enough for the engine to be well warmed up, let it set for 10 minutes, or so, and pull the fuel line off the carburetor to see if there is a pressure buildup in the line. Let the car set for another 20 minutes and pull the top off the carburetor and see how much fuel is in the fuel bowls. If either bowl is empty, add fuel to it and watch the level.

 

 

“If you can't explain it simply, you don't understand it well enough.”

--Albert Einstein

 

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Because you've already tried a spacer (assuming it's not metal) you shouldn't be getting fuel bowl percolation, especially in the winter. If the fuel line between the fuel pump and carburetor is too close to, or touching, the engine, fuel could be percolating in the line and causing a flooding problem. I have seen carburetors with porous castings that allow fuel to drain into the intake manifold. Sometime after you have been driving long enough for the engine to be well warmed up, let it set for 10 minutes, or so, and pull the fuel line off the carburetor to see if there is a pressure buildup in the line. Let the car set for another 20 minutes and pull the top off the carburetor and see how much fuel is in the fuel bowls. If either bowl is empty, add fuel to it and watch the level.

 

Thanks Don. Unfortunately it is a metal spacer as the limiting factor is I'm using the stock 73 manifold which has the egr opening. The stock spacer covers that. All the aftermarket ones our there aren't the right shape. I know someday I'll be changing the manifold but have been putting it off. I was just wondering if the holly functions better or if going back fully to stock might be another solution.

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Back in the day I had a Holly with the stock 73 4v intake and a aluminum adapter and my car never ran right. I wound up using the 4300D carb. Just my experiences with this setup.

-john

(jbojo)

351C 4V cc heads, 10.5 : 1 CR, 290 Herbert cam, Flat top forged pistons, forged connecting rods, Atomic efi,

C6 with Gear Vendor overdrive, 3.89 Tru Trac, Hooker Super Comp with 2 1/2" Pypes Exhaust.        

 

Some Mod pictures can be seen at: [button=http://www.7173mustangs.com/forum-garage?filterxt_uid=2026]Bojo's Garage[/button]

 

 

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Heat Soak

 

http://www.edelblog.com/tech-tips/resolving-heat-soak/

 

I have no issue with the Edelbrock manifold/carb/insulating gasket combo.

 

Paul

73 Grande

351C 2v

Now 4v Carb/Cam/headers/T5

 

Gasoline is for washing parts.

Alcohol is for drinking.

Nitomethane is for racing!

 

 

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Last Update: 4/23/16

 

http://s1270.photobucket.com/user/therocket366/library/?sort=3&page=1

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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In my experience, I loved my Edelbrock for about 2 days, same model 1406, but on an aftermarket manifold. I never got that carburetor running right, even taking it to the "best" carb guy in town. If I could go back and change it all I would have spent the extra money on a fuel injection system or a quick fuel carb. Now I am running a rebuilt Autolite 2100 on the stock manifold and it runs great!

1_12_09_14_10_32_45.png

 

- Nik

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Heat Soak

 

http://www.edelblog.com/tech-tips/resolving-heat-soak/

 

I have no issue with the Edelbrock manifold/carb/insulating gasket combo.

 

Paul

I've limited my hood clearance by using ram air set up but I think I am going to look for an insulating gasket beneath the carb and see if that doesn't isolate the carb a bit and help alleviate the soak.

Ordered one up.

Also, I am using a metal fuel filter that is near the front of the carb. I've avoided the plastic ones for fear of melt through but is the metal filter also transferring heat to the line? Any better alternatives and....anyone have a photo of how they have their fuel line routed? Maybe I can do better about getting it away from the heat of the engine.

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Heat Soak

 

http://www.edelblog.com/tech-tips/resolving-heat-soak/

 

I have no issue with the Edelbrock manifold/carb/insulating gasket combo.

 

Paul

I've limited my hood clearance by using ram air set up but I think I am going to look for an insulating gasket beneath the carb and see if that doesn't isolate the carb a bit and help alleviate the soak.

Ordered one up.

Also, I am using a metal fuel filter that is near the front of the carb. I've avoided the plastic ones for fear of melt through but is the metal filter also transferring heat to the line? Any better alternatives and....anyone have a photo of how they have their fuel line routed? Maybe I can do better about getting it away from the heat of the engine.

 

There may be enough space at the inlet to the fuel pump to install a filter like this. http://www.summitracing.com/parts/rus-645150/overview/

Chuck

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if you have a 1/2 of space to spare, adding a wood carb spacer works well to isolate the carb from the intake manifold heat. I personally believe they work better than even the phenolic resin spacers.

 

You can also insulate your fuel line and even your fuel filter using DEI heat sheath insulation.

 

What is your hot start starting procedure? Are you giving it any gas at all before cranking and if so how much?

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"I love my Hookers!" and "Get some Strange" probably have a different connotation to non automotive enthusiasts!

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I have a relatively new Edlebrock 1406 on a stock manifold with a 1973 351 4V. The car is believed to have a non stock cam although I do not have the numbers. Mild at best.

New fuel pump. ignition conversion. No more points.

The problem I have seems to be very common. The car starts great when cold and will start again perfectly a few minutes later once shut off. Idle is fine and performance seems appropriate.

However, summer and winter once it has been run for a 1/2 hour lets say and parked for more than 15 minutes it is pretty tough to get to crank over - although it always does. One day I assume I will kill a battery.

I've experimented with carb settings, (with my limited abilities) and different throttle positions when cranking. From what I read this is likely a fuel boiling or draining issue and is somewhat "normal" with this carb. A spacer in this case hasn't helped and this happened with both the old 1406 and a newer one. The fuel filter is near the manifold so maybe I could try and isolate that better if the fuel is being boiled out of there.

My question is would for example a Holley 750cfm be less prone to this issue or am I just spending money for no reason? Can I improve the 1406 or just give it up and make a switch and get better starting and performance? If so, is the Holley more difficult to dial in?

I feel like the Edlebrock is a simple carb (perfect for me) but that might also be limiting in terms of its performance in this case. I know there are some Edlebrock carb haters here and this may be why!

 

I also have some of the stock parts to convert the car back to the original carb. set up. Would this be a waste of effort in terms of reliability and performance and more aggravation - with the only benefit being it is now correct (which I like but it is not vital)?

Thanks for your help.

Jeff

 

You say you have a stock manifold. To be honest, I am not familiar with the 73 4V manifold or the Edlebrock as mine is a 71 4V with a Holley, but I was experiencing much the same problem. my engine was rebuilt and I changed my old carb to a Holley 670 Street Avenger which ran well right out of the box. The problem was almost exactly as yours. My factory manifold has heat riser passages which I had already blocked off at the carb base with set screws, Not enough to cut down the heat, so I removed the intake and hand 'milled' a step in each one of the exhaust heat riser openings and plugged it with a piece of 1/16th thick SS. These were 'stitched in' and covered with a layer of high heat cement. I also used a thin piece of SS, .020", cut slightly larger than the opening on the heads, inserted that into the .020" FelPro gasket with some more cement, replaced the valley pan and bolted it all back together. The result was immediate and the heat under the carb was reduced big time. I do use a 1" Micarda (fiber) insulator, but I am sure a 1/4" heat spacer would be OK as I think you are using Ram Air. In short, my car starts every time with no issues. The old 4300 series carbs were design to work with the heat risers, newer ones aren't.

This is a job that does require some machining type skills, but it worked for me. Hope this helps you solve your problem. One more thing. When my car was put on a dyno (for another problem) the fuel/ air ratios were near perfect with the 670cfm. Personally I think a 750 is on the big side without re-jetting it, but I'm far from being an expert on that, so chose what is right for you.

Geoff.

Geoff.

 I learn something new every day!

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I have a relatively new Edlebrock 1406 on a stock manifold with a 1973 351 4V. The car is believed to have a non stock cam although I do not have the numbers. Mild at best.

New fuel pump. ignition conversion. No more points.

The problem I have seems to be very common. The car starts great when cold and will start again perfectly a few minutes later once shut off. Idle is fine and performance seems appropriate.

However, summer and winter once it has been run for a 1/2 hour lets say and parked for more than 15 minutes it is pretty tough to get to crank over - although it always does. One day I assume I will kill a battery.

I've experimented with carb settings, (with my limited abilities) and different throttle positions when cranking. From what I read this is likely a fuel boiling or draining issue and is somewhat "normal" with this carb. A spacer in this case hasn't helped and this happened with both the old 1406 and a newer one. The fuel filter is near the manifold so maybe I could try and isolate that better if the fuel is being boiled out of there.

My question is would for example a Holley 750cfm be less prone to this issue or am I just spending money for no reason? Can I improve the 1406 or just give it up and make a switch and get better starting and performance? If so, is the Holley more difficult to dial in?

I feel like the Edlebrock is a simple carb (perfect for me) but that might also be limiting in terms of its performance in this case. I know there are some Edlebrock carb haters here and this may be why!

 

I also have some of the stock parts to convert the car back to the original carb. set up. Would this be a waste of effort in terms of reliability and performance and more aggravation - with the only benefit being it is now correct (which I like but it is not vital)?

Thanks for your help.

Jeff

 

You say you have a stock manifold. To be honest, I am not familiar with the 73 4V manifold or the Edlebrock as mine is a 71 4V with a Holley, but I was experiencing much the same problem. my engine was rebuilt and I changed my old carb to a Holley 670 Street Avenger which ran well right out of the box. The problem was almost exactly as yours. My factory manifold has heat riser passages which I had already blocked off at the carb base with set screws, Not enough to cut down the heat, so I removed the intake and hand 'milled' a step in each one of the exhaust heat riser openings and plugged it with a piece of 1/16th thick SS. These were 'stitched in' and covered with a layer of high heat cement. I also used a thin piece of SS, .020", cut slightly larger than the opening on the heads, inserted that into the .020" FelPro gasket with some more cement, replaced the valley pan and bolted it all back together. The result was immediate and the heat under the carb was reduced big time. I do use a 1" Micarda (fiber) insulator, but I am sure a 1/4" heat spacer would be OK as I think you are using Ram Air. In short, my car starts every time with no issues. The old 4300 series carbs were design to work with the heat risers, newer ones aren't.

This is a job that does require some machining type skills, but it worked for me. Hope this helps you solve your problem. One more thing. When my car was put on a dyno (for another problem) the fuel/ air ratios were near perfect with the 670cfm. Personally I think a 750 is on the big side without re-jetting it, but I'm far from being an expert on that, so chose what is right for you.

Geoff.

Thanks Geoff. Great info. I'm almost wondering if I plan on sticking with the stock intake if it might be interesting and even more efficient to use a 4300D and put it back to stock the way it was designed to work.


if you have a 1/2 of space to spare, adding a wood carb spacer works well to isolate the carb from the intake manifold heat. I personally believe they work better than even the phenolic resin spacers.

 

You can also insulate your fuel line and even your fuel filter using DEI heat sheath insulation.

 

What is your hot start starting procedure? Are you giving it any gas at all before cranking and if so how much?

 

Thanks Jeff. I heard wood was great for this but it always makes me nervous - the idea of using wood in that environment yet I understand it has bene done for years. One option that would be easier to do in wood than any other medium is that I could cut my own spacer to mimic the stock one on there now and just eliminate the EGR passages etc. It would then cover what it needed to on the manifold plus provide great insulation properties. (and I can have fun trying to cut my own spacer. The kids love hearing me curse)


Heat Soak

 

http://www.edelblog.com/tech-tips/resolving-heat-soak/

 

I have no issue with the Edelbrock manifold/carb/insulating gasket combo.

 

Paul

I've limited my hood clearance by using ram air set up but I think I am going to look for an insulating gasket beneath the carb and see if that doesn't isolate the carb a bit and help alleviate the soak.

Ordered one up.

Also, I am using a metal fuel filter that is near the front of the carb. I've avoided the plastic ones for fear of melt through but is the metal filter also transferring heat to the line? Any better alternatives and....anyone have a photo of how they have their fuel line routed? Maybe I can do better about getting it away from the heat of the engine.

 

There may be enough space at the inlet to the fuel pump to install a filter like this. http://www.summitracing.com/parts/rus-645150/overview/

Chuck

That's the kind of filter I am looking for. Even if I cant get it near the pump its a much narrower design than what I am using. So, it wont sit as close to the manifold or any other hot parts and might cool off easier. That large air cleaner housing probably traps a lot of rising heat under it and my fuel line and filter run right there as well.

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Jeff

 

You say you have a stock manifold. To be honest, I am not familiar with the 73 4V manifold or the Edlebrock as mine is a 71 4V with a Holley, but I was experiencing much the same problem. my engine was rebuilt and I changed my old carb to a Holley 670 Street Avenger which ran well right out of the box. The problem was almost exactly as yours. My factory manifold has heat riser passages which I had already blocked off at the carb base with set screws, Not enough to cut down the heat, so I removed the intake and hand 'milled' a step in each one of the exhaust heat riser openings and plugged it with a piece of 1/16th thick SS. These were 'stitched in' and covered with a layer of high heat cement. I also used a thin piece of SS, .020", cut slightly larger than the opening on the heads, inserted that into the .020" FelPro gasket with some more cement, replaced the valley pan and bolted it all back together. The result was immediate and the heat under the carb was reduced big time. I do use a 1" Micarda (fiber) insulator, but I am sure a 1/4" heat spacer would be OK as I think you are using Ram Air. In short, my car starts every time with no issues. The old 4300 series carbs were design to work with the heat risers, newer ones aren't.

This is a job that does require some machining type skills, but it worked for me. Hope this helps you solve your problem. One more thing. When my car was put on a dyno (for another problem) the fuel/ air ratios were near perfect with the 670cfm. Personally I think a 750 is on the big side without re-jetting it, but I'm far from being an expert on that, so chose what is right for you.

Geoff.

Thanks Geoff. Great info. I'm almost wondering if I plan on sticking with the stock intake if it might be interesting and even more efficient to use a 4300D and put it back to stock the way it was designed to work.

 

 

Thanks Jeff. I heard wood was great for this but it always makes me nervous - the idea of using wood in that environment yet I understand it has bene done for years. One option that would be easier to do in wood than any other medium is that I could cut my own spacer to mimic the stock one on there now and just eliminate the EGR passages etc. It would then cover what it needed to on the manifold plus provide great insulation properties. (and I can have fun trying to cut my own spacer. The kids love hearing me curse)


I've limited my hood clearance by using ram air set up but I think I am going to look for an insulating gasket beneath the carb and see if that doesn't isolate the carb a bit and help alleviate the soak.

Ordered one up.

Also, I am using a metal fuel filter that is near the front of the carb. I've avoided the plastic ones for fear of melt through but is the metal filter also transferring heat to the line? Any better alternatives and....anyone have a photo of how they have their fuel line routed? Maybe I can do better about getting it away from the heat of the engine.

 

Jeff, I have my primary filter mounted right where the fuel line comes through the apron and before the pump, a steel one of course!! Never would I use plastic or glass.... ever! The Holley has sintered bronze filters in each of the inlets to the fuel bowls.

As for the spacer, the material I used is commonly used in the electrical industry as an insulator. I know it as Micarda. It is a very dense fiber material and is excellent for a carb spacer although it might appear to absorb some gas over time, but so far without issue. Being a machinist, I was able to mill and taper bore the ports for an exact match. There are similar materials out there and McMaster & Carr should carry this.

Geoff.

 I learn something new every day!

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Jeff

 

You say you have a stock manifold. To be honest, I am not familiar with the 73 4V manifold or the Edlebrock as mine is a 71 4V with a Holley, but I was experiencing much the same problem. my engine was rebuilt and I changed my old carb to a Holley 670 Street Avenger which ran well right out of the box. The problem was almost exactly as yours. My factory manifold has heat riser passages which I had already blocked off at the carb base with set screws, Not enough to cut down the heat, so I removed the intake and hand 'milled' a step in each one of the exhaust heat riser openings and plugged it with a piece of 1/16th thick SS. These were 'stitched in' and covered with a layer of high heat cement. I also used a thin piece of SS, .020", cut slightly larger than the opening on the heads, inserted that into the .020" FelPro gasket with some more cement, replaced the valley pan and bolted it all back together. The result was immediate and the heat under the carb was reduced big time. I do use a 1" Micarda (fiber) insulator, but I am sure a 1/4" heat spacer would be OK as I think you are using Ram Air. In short, my car starts every time with no issues. The old 4300 series carbs were design to work with the heat risers, newer ones aren't.

This is a job that does require some machining type skills, but it worked for me. Hope this helps you solve your problem. One more thing. When my car was put on a dyno (for another problem) the fuel/ air ratios were near perfect with the 670cfm. Personally I think a 750 is on the big side without re-jetting it, but I'm far from being an expert on that, so chose what is right for you.

Geoff.

Thanks Geoff. Great info. I'm almost wondering if I plan on sticking with the stock intake if it might be interesting and even more efficient to use a 4300D and put it back to stock the way it was designed to work.

 

 

Thanks Jeff. I heard wood was great for this but it always makes me nervous - the idea of using wood in that environment yet I understand it has bene done for years. One option that would be easier to do in wood than any other medium is that I could cut my own spacer to mimic the stock one on there now and just eliminate the EGR passages etc. It would then cover what it needed to on the manifold plus provide great insulation properties. (and I can have fun trying to cut my own spacer. The kids love hearing me curse)


I've limited my hood clearance by using ram air set up but I think I am going to look for an insulating gasket beneath the carb and see if that doesn't isolate the carb a bit and help alleviate the soak.

Ordered one up.

Also, I am using a metal fuel filter that is near the front of the carb. I've avoided the plastic ones for fear of melt through but is the metal filter also transferring heat to the line? Any better alternatives and....anyone have a photo of how they have their fuel line routed? Maybe I can do better about getting it away from the heat of the engine.

 

Jeff, I have my primary filter mounted right where the fuel line comes through the apron and before the pump, a steel one of course!! Never would I use plastic or glass.... ever! The Holley has sintered bronze filters in each of the inlets to the fuel bowls.

As for the spacer, the material I used is commonly used in the electrical industry as an insulator. I know it as Micarda. It is a very dense fiber material and is excellent for a carb spacer although it might appear to absorb some gas over time, but so far without issue. Being a machinist, I was able to mill and taper bore the ports for an exact match. There are similar materials out there and McMaster & Carr should carry this.

That is where I would like to move the filter. Also, I had heard about Micarda and that company so I will check there. Not being a machinest my results might be a little less umm attractive as yours turned out. I will start with the filer and insulating the fuel lines.

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Jeff

 

You say you have a stock manifold. To be honest, I am not familiar with the 73 4V manifold or the Edlebrock as mine is a 71 4V with a Holley, but I was experiencing much the same problem. my engine was rebuilt and I changed my old carb to a Holley 670 Street Avenger which ran well right out of the box. The problem was almost exactly as yours. My factory manifold has heat riser passages which I had already blocked off at the carb base with set screws, Not enough to cut down the heat, so I removed the intake and hand 'milled' a step in each one of the exhaust heat riser openings and plugged it with a piece of 1/16th thick SS. These were 'stitched in' and covered with a layer of high heat cement. I also used a thin piece of SS, .020", cut slightly larger than the opening on the heads, inserted that into the .020" FelPro gasket with some more cement, replaced the valley pan and bolted it all back together. The result was immediate and the heat under the carb was reduced big time. I do use a 1" Micarda (fiber) insulator, but I am sure a 1/4" heat spacer would be OK as I think you are using Ram Air. In short, my car starts every time with no issues. The old 4300 series carbs were design to work with the heat risers, newer ones aren't.

This is a job that does require some machining type skills, but it worked for me. Hope this helps you solve your problem. One more thing. When my car was put on a dyno (for another problem) the fuel/ air ratios were near perfect with the 670cfm. Personally I think a 750 is on the big side without re-jetting it, but I'm far from being an expert on that, so chose what is right for you.

Geoff.

Thanks Geoff. Great info. I'm almost wondering if I plan on sticking with the stock intake if it might be interesting and even more efficient to use a 4300D and put it back to stock the way it was designed to work.

 

 

Thanks Jeff. I heard wood was great for this but it always makes me nervous - the idea of using wood in that environment yet I understand it has bene done for years. One option that would be easier to do in wood than any other medium is that I could cut my own spacer to mimic the stock one on there now and just eliminate the EGR passages etc. It would then cover what it needed to on the manifold plus provide great insulation properties. (and I can have fun trying to cut my own spacer. The kids love hearing me curse)


I've limited my hood clearance by using ram air set up but I think I am going to look for an insulating gasket beneath the carb and see if that doesn't isolate the carb a bit and help alleviate the soak.

Ordered one up.

Also, I am using a metal fuel filter that is near the front of the carb. I've avoided the plastic ones for fear of melt through but is the metal filter also transferring heat to the line? Any better alternatives and....anyone have a photo of how they have their fuel line routed? Maybe I can do better about getting it away from the heat of the engine.

 

Jeff, I have my primary filter mounted right where the fuel line comes through the apron and before the pump, a steel one of course!! Never would I use plastic or glass.... ever! The Holley has sintered bronze filters in each of the inlets to the fuel bowls.

As for the spacer, the material I used is commonly used in the electrical industry as an insulator. I know it as Micarda. It is a very dense fiber material and is excellent for a carb spacer although it might appear to absorb some gas over time, but so far without issue. Being a machinist, I was able to mill and taper bore the ports for an exact match. There are similar materials out there and McMaster & Carr should carry this.

That is where I would like to move the filter. Also, I had heard about Micarda and that company so I will check there. Not being a machinest my results might be a little less umm attractive as yours turned out. I will start with the filer and insulating the fuel lines.

 

To be honest, I thought that they all had the primary fuel filters located between the apron and fuel pump. I have owned 4 mach1's and as far as I can remember, that was the location on all of them. Time flies, memory fades!

As for reusing the 4300D, I read that they are not that good, horrible to tune, but good for the authentic look, just saying. There may be another option for a carb that is supposed to be better than the Holley and that is the Quick Fuel carburetor. I would seriously look at this brand if I were buying another for my car. However, its your decision to make, it's your car. Good luck.

Geoff.

Geoff.

 I learn something new every day!

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Jeff

 

You say you have a stock manifold. To be honest, I am not familiar with the 73 4V manifold or the Edlebrock as mine is a 71 4V with a Holley, but I was experiencing much the same problem. my engine was rebuilt and I changed my old carb to a Holley 670 Street Avenger which ran well right out of the box. The problem was almost exactly as yours. My factory manifold has heat riser passages which I had already blocked off at the carb base with set screws, Not enough to cut down the heat, so I removed the intake and hand 'milled' a step in each one of the exhaust heat riser openings and plugged it with a piece of 1/16th thick SS. These were 'stitched in' and covered with a layer of high heat cement. I also used a thin piece of SS, .020", cut slightly larger than the opening on the heads, inserted that into the .020" FelPro gasket with some more cement, replaced the valley pan and bolted it all back together. The result was immediate and the heat under the carb was reduced big time. I do use a 1" Micarda (fiber) insulator, but I am sure a 1/4" heat spacer would be OK as I think you are using Ram Air. In short, my car starts every time with no issues. The old 4300 series carbs were design to work with the heat risers, newer ones aren't.

This is a job that does require some machining type skills, but it worked for me. Hope this helps you solve your problem. One more thing. When my car was put on a dyno (for another problem) the fuel/ air ratios were near perfect with the 670cfm. Personally I think a 750 is on the big side without re-jetting it, but I'm far from being an expert on that, so chose what is right for you.

Geoff.

Thanks Geoff. Great info. I'm almost wondering if I plan on sticking with the stock intake if it might be interesting and even more efficient to use a 4300D and put it back to stock the way it was designed to work.

 

 

Thanks Jeff. I heard wood was great for this but it always makes me nervous - the idea of using wood in that environment yet I understand it has bene done for years. One option that would be easier to do in wood than any other medium is that I could cut my own spacer to mimic the stock one on there now and just eliminate the EGR passages etc. It would then cover what it needed to on the manifold plus provide great insulation properties. (and I can have fun trying to cut my own spacer. The kids love hearing me curse)


I've limited my hood clearance by using ram air set up but I think I am going to look for an insulating gasket beneath the carb and see if that doesn't isolate the carb a bit and help alleviate the soak.

Ordered one up.

Also, I am using a metal fuel filter that is near the front of the carb. I've avoided the plastic ones for fear of melt through but is the metal filter also transferring heat to the line? Any better alternatives and....anyone have a photo of how they have their fuel line routed? Maybe I can do better about getting it away from the heat of the engine.

 

Jeff, I have my primary filter mounted right where the fuel line comes through the apron and before the pump, a steel one of course!! Never would I use plastic or glass.... ever! The Holley has sintered bronze filters in each of the inlets to the fuel bowls.

As for the spacer, the material I used is commonly used in the electrical industry as an insulator. I know it as Micarda. It is a very dense fiber material and is excellent for a carb spacer although it might appear to absorb some gas over time, but so far without issue. Being a machinist, I was able to mill and taper bore the ports for an exact match. There are similar materials out there and McMaster & Carr should carry this.

That is where I would like to move the filter. Also, I had heard about Micarda and that company so I will check there. Not being a machinest my results might be a little less umm attractive as yours turned out. I will start with the filer and insulating the fuel lines.

 

To be honest, I thought that they all had the primary fuel filters located between the apron and fuel pump. I have owned 4 mach1's and as far as I can remember, that was the location on all of them. Time flies, memory fades!

As for reusing the 4300D, I read that they are not that good, horrible to tune, but good for the authentic look, just saying. There may be another option for a carb that is supposed to be better than the Holley and that is the Quick Fuel carburetor. I would seriously look at this brand if I were buying another for my car. However, its your decision to make, it's your car. Good luck.

Geoff.

I'll take it one step at a time. I know that in the end, the stock manifold on the 73 is my limiting factor. I have that nice j channel with an opening leading into the engine where hot exhaust probably runs right into the metal stock spacer plate, heats it up and in turns heats the carb - plus the extraneous engine heat on the fuel supply system as well. If I keep this set up I am going to try a thin insulating gasket (clearance issues) along with the other items such as the filter relocation and fuel line insulation but ultimately I'll probably try and make a spacer to really insulate the carb from the heat. Thanks for all the input.

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I have seen that channel filled with steel epoxy on an old manifold. I also pulled a wood gasket off of mine 3-4 years ago during a carb/intake swap. The wood seems to hold up quite well. If you can draw a pattern for the insulator it isn't hard to make one and you could use 1/4 or 3/8th plywood to make it and keep the height at a manageable level.

 

Make it from something like a basaltic birch cabinet plywood. You can seal it with a bit of resin and hardener if you want, or even spray it with a couple coats of urethane. use a gasket above and below it and don't overtighten it as the ears tend to be a bit fragile, plan to retorque it after a few hours use,

 

If you don't feel comfortable cutting it out, you can send me the pattern and I'll cut one for you.

http://www.7173mustangs.com/gallery/1_01_07_15_8_53_18.png

 

"I love my Hookers!" and "Get some Strange" probably have a different connotation to non automotive enthusiasts!

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A final thought. I was thinking about spacers and decided to check my Carb bits box. I have a 1/4" insulator gasket that I purchased at the local rod-rod store. This one is not a spread bore, but I would have to think they make one. If you can find one of these, then hopefully, problem solved. If you do not plug the heat riser passages, there is a bottom basket with a metal insert (between the top and bottom paper layers) that you would also need. You would need this gasket if you decide to go back to the 4300D. I can't help with numbers as like I said, my stuff is not spread bore. My thought on blocking the risers is it creates a dead air space, a good insulator, whereas high temp putty would still transfer some heat. That's my theory and I'm sticking with it!!!!

Let us all know how it works out for you.

Geoff.

Geoff.

 I learn something new every day!

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Cranking just fine when warm. Not more slowly. Soubds strong. Just won't catch without multiple attempts and various machinations with the gas pedal.

 

Simple.

 

1. Look in the front carb venturis and slowly open the throttle 1/8th and see if it shoots two streams of gas . If it does not, that is part of the prob.

 

2. Advance the timing 4 degrees when it is hot and see what happens.

 

3. If you plug the vacuum advance and advance the timing 4 degrees at idle and the rpm goes up and it still runs smoothly, it needs more idle timing.

 

4. If you do the same thing at around 2000 rpm and the rpm goes up and it runs smoothly it needs more timing there also.

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Cranking just fine when warm. Not more slowly. Soubds strong. Just won't catch without multiple attempts and various machinations with the gas pedal.

 

Simple.

 

1. Look in the front carb venturis and slowly open the throttle 1/8th and see if it shoots two streams of gas . If it does not, that is part of the prob.

 

2. Advance the timing 4 degrees when it is hot and see what happens.

 

3. If you plug the vacuum advance and advance the timing 4 degrees at idle and the rpm goes up and it still runs smoothly, it needs more idle timing.

 

4. If you do the same thing at around 2000 rpm and the rpm goes up and it runs smoothly it needs more timing there also.

Got it. Thanks


A final thought. I was thinking about spacers and decided to check my Carb bits box. I have a 1/4" insulator gasket that I purchased at the local rod-rod store. This one is not a spread bore, but I would have to think they make one. If you can find one of these, then hopefully, problem solved. If you do not plug the heat riser passages, there is a bottom basket with a metal insert (between the top and bottom paper layers) that you would also need. You would need this gasket if you decide to go back to the 4300D. I can't help with numbers as like I said, my stuff is not spread bore. My thought on blocking the risers is it creates a dead air space, a good insulator, whereas high temp putty would still transfer some heat. That's my theory and I'm sticking with it!!!!

Let us all know how it works out for you.

Geoff.

Thanks Geoff. Working it all out now. One other thing. Do you know if the Id of the fuel line running from the fender apron to the pump is normally 3/8? Thanks.

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