Jump to content

Low RPM Drivability Issue / 1973 351C


Recommended Posts

51 minutes ago, 73inNH said:

I suspect you're right. Problem is, it's already on the top hole and I bent the rod to get a bigger shot. I'm pretty maxed out . . .

I'll continue to check for other air leaks. Maybe I'm missing something.

Then you'll need to increase the size of the discharge nozzle to deliver a faster pump shot. You can drill them if you have the appropriate size drill bits, or get the kit from Edelbrock. 

https://www.summitracing.com/parts/edl-1475

 

 

Link to comment
Share on other sites

44 minutes ago, 73inNH said:

On the passenger side near the firewall, they're the large blue can and a small black coffee can. The small black can connect to a vacuum port on the manifold and the other side appears to go through the firewall into the car.

What is that? I don't detect a leak there with carburetor cleaner, but I'm wondering if I should disconnect that hose and plug the manifold port while I troubleshoot.

Black can is a vacuum accumulator / check valve so you have steady vac to run your heater / ac actuators.  You could pull it off and plug it for curiosity.

Link to comment
Share on other sites

1 hour ago, boilermaster said:

73inNH.

Bentworker makes a good point.

if you adjusted your idle mixture with the pcv disconnected and plugged and then added it to the mix you are going to be leaner than you were before, also what pcv valve are you using ? different pcv valves have different metering values.

I too like the ME wagner adjustable pcv valve, also 650 rpm idle speed seems a tad low (by todays standards) unless you have a totally stock engine and I have no clue how the transfer slots work on your particular carb.

Agreed. I'll reconnect the PCV this weekend and reset the idle air screws to see if it helps. It makes sense . . .

Link to comment
Share on other sites

Hard to be precise looking at pictures but, the dark soot ring and perhaps the soot on the center electrode indicate a slightly rich condition at idle. Where the ground strap changes colors seems to indicate initial and total are right or very close to it. Might be a bit lean at WOT but you really need to look at the base of the porcelain, not the electrode end, to tell. You can buy a plug reading light, or cut the threaded portion of one plug off and look for a ring where the porcelain meets the steel body. I hope you get it sorted out. Chuck

Link to comment
Share on other sites

An update . . .

Thinking about the PCV and how when I connect it to the PCV port on the carb, the car bogs (running lean, likely), I decided to plumb the PCV into the air cleaner base. As I was looking at my setup, I remembered that the PCV was originally plumbed into the stock air cleaner housing, not the carb. When I switched to the Edelbrock 14" air cleaner, I plumbed it into the carb, which caused the bog.

So I bought an elbow and a grommet, drilled out a hole in the air cleaner base, and run a small hose from the base to the PCV in the valve cover. This worked. I now have the PCV connected, and the engine runs well. I still have a very small hesitation when mashing the throttle from low RPMs. I may buy the Edelbrock accelerator pump tuning kit to give it a bigger shot, but the problem is so small now that I'm in no rush. 

Link to comment
Share on other sites

73inNH,

Just to be 100% clear here,

The OEM pcv setup on our cars were designed to have a vacuum side and a pressure side.

The vacuum side consists of a vacuum port at the carb (or spacer under the carb) for pcv vacuum

and pcv valve in the left rocker cover.

The pcv pressure side consists of  a grommet, elbows and an attachment to the air cleaner to allow the  pressure side to be drawn into the air cleaner to allow the system to flow.

If you don't allow the system to actually flow, all you are getting is a metered vacuum leak.

FWIW, If you are running stock valve covers with a twist on oil cap make sure the cap still has baffeling material in it.

If you are running aftermarket covers with press in covers you need to have a way to baffle the oil or you will end up with oil being sucked thru the pcv system and an oil consumption issue and possible engine damage.

I think you are doing this correctly, just want to be 100% thanks for understanding.

Boilermaster

Link to comment
Share on other sites

@boilermaster

My exact setup:

1. Run of the mill breather in passenger side valve cover.

2. PCV in driver side oil cap.

3. Hose from PCV to 14 round Edelbrock air cleaner.

A pic of my oil cap is attached.

Will this work well?

 

PXL_20210915_160535374.jpg

Edited by 73inNH
Link to comment
Share on other sites

1 hour ago, 73inNH said:

So I bought an elbow and a grommet,

I've been following this topic pretty closely because your problem sounds an awful a lot like mine: Bogging down when mashing down on the gas pedal.  I also have an Edelbrock Performer intake but with an Edelbrock 1406 carb. When I swapped out the intake and carb I plumbed the PCV valve into the carb like you did. Maybe this is my my issue too.

So, would you happen to still have the specs on the elbow and grommet you purchased? I'd like to see if that helps me out too.

Thanks,

Mike

 

Link to comment
Share on other sites

2 minutes ago, mjseakan said:

I've been following this topic pretty closely because your problem sounds an awful a lot like mine: Bogging down when mashing down on the gas pedal.  I also have an Edelbrock Performer intake but with an Edelbrock 1406 carb. When I swapped out the intake and carb I plumbed the PCV valve into the carb like you did. Maybe this is my my issue too.

So, would you happen to still have the specs on the elbow and grommet you purchased? I'd like to see if that helps me out too.

Thanks,

Mike

 

Mike,

Before spending any money, disconnect the PCV valve and plug the fitting on the carburetor and drive. If your problem is similar to mine your car will likely be substantially better after doing that. Then you can figure out next steps.

 

Link to comment
Share on other sites

73inNH,

IF your breather in the passenger side is open to the atmosphere , it has to overcome atmospheric pressure to flow.

If the breather is inside the air cleaner (as this system was stock) it uses the engines intake airflow to overcome that atmospheric pressure in order to work properly.

pressure and vacuum always trying to equalize, it's a funny thing.

Boilermaster  

  • Like 1
Link to comment
Share on other sites

55 minutes ago, 73inNH said:

@boilermaster

My exact setup:

1. Run of the mill breather in passenger side valve cover.

2. PCV in driver side oil cap.

3. Hose from PCV to 14 round Edelbrock air cleaner.

A pic of my oil cap is attached.

Will this work well?

 

There is not enough vacuum in the air cleaner (unless the filter element is plugged with dirt) to draw in the fumes from the crankcase. Both the breather and PCV are basically operating at atmospheric pressure. For it to function and evacuate the fumes the PCV valve must be plumbed into the intake. The fumes consist of moisture, unburned fuel and vapors from the engine oil, not something you want to stay in the crankcase and turn into corrosive goop.

The breather side of the system is plumbed into the air filter housing to provide a clean air source so that dust and dirt is not drawn into the crankcase.

The need for removing the fumes was recognized way back, and the original system was what was called a road draft tube to draw out the fumes and a breather cap that had some filtering built into it.

  • Like 1

 

 

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

--Albert Einstein

 

Link to comment
Share on other sites

8 minutes ago, Don C said:

There is not enough vacuum in the air cleaner (unless the filter element is plugged with dirt) to draw in the fumes from the crankcase. Both the breather and PCV are basically operating at atmospheric pressure. For it to function and evacuate the fumes the PCV valve must be plumbed into the intake. The fumes consist of moisture, unburned fuel and vapors from the engine oil, not something you want to stay in the crankcase and turn into corrosive goop.

The breather side of the system is plumbed into the air filter housing to provide a clean air source so that dust and dirt is not drawn into the crankcase.

The need for removing the fumes was recognized way back, and the original system was what was called a road draft tube to draw out the fumes and a breather cap that had some filtering built into it.

In essence, I want:

1. Driver's side PCV valve to PCV port on carb (which has given me problems, but I can revisit).

2. Passenger side breather replaced with hose to air cleaner.

That will give me a properly functioning PCV system, correct?

Link to comment
Share on other sites

4 minutes ago, Don C said:

Yes, that will give you a functioning system. Make sure the PCV valve is correct for your engine and that the valve inside of it moves. When you shake it up and down you'll hear it move. The valve is controlled by a calibrated spring. Under high manifold vacuum the valve is partially closed, limiting the amount of extra air entering the manifold and reducing the lean condition. Under acceleration, when the manifold vacuum is low, the valve opens further, this is also when the most bypass fumes enter the crankcase. If the engine backfires the valve closes to prevent it from entering the crankcase.

Got it.

OK, I'll work on the issues I have when the PCV is connected. It's fixable. . . . the extra air is leaning out the carb. I'll get it.

Thanks, Don and boilermaster.

 

Link to comment
Share on other sites

73inNH,

DonC, as usual nailed it.

With just a breather on the passenger side rocker cover (open to atmosphere) and the pcv valve connected to the pcv port on your carb, you would have what is called an (open pcv system)

With the breather going to the carb, you will have a (closed pcv system) which is more efficient.

PCV valve selection is Critical, 

Link to comment
Share on other sites

1 minute ago, boilermaster said:

73inNH,

DonC, as usual nailed it.

With just a breather on the passenger side rocker cover (open to atmosphere) and the pcv valve connected to the pcv port on your carb, you would have what is called an (open pcv system)

With the breather going to the carb, you will have a (closed pcv system) which is more efficient.

PCV valve selection is Critical, 

Awesome. You guys make life much easier. Thank you.

Link to comment
Share on other sites

1 hour ago, mjseakan said:

I've been following this topic pretty closely because your problem sounds an awful a lot like mine: Bogging down when mashing down on the gas pedal.  I also have an Edelbrock Performer intake but with an Edelbrock 1406 carb. When I swapped out the intake and carb I plumbed the PCV valve into the carb like you did. Maybe this is my my issue too.

So, would you happen to still have the specs on the elbow and grommet you purchased? I'd like to see if that helps me out too.

Thanks,

Mike

 

My guess is you need to swap out for stiffer springs.  Your secondaries are opening up before the secondary jets pop up and provide the fuel you need.

  • Thanks 1

Jason (71 Mach 1, 351C 4V, 4 Spd. Toploader, Grabber Blue)

Link to comment
Share on other sites

73inNH,

Motorcraft EV50 pcv valve comes to mind as a small orifice pcv valve for the Cleveland engines.

As for the bog, has correct fuel pressure been verified ?

Fairly easy with a Holley vacuum secondary carb when the secondary spring is too weak, don't know on the AVS if there is a way to Deactivate the secondary linkage or not.

  • Like 1
Link to comment
Share on other sites

On 9/10/2021 at 12:41 PM, boilermaster said:

73inNH.

Bentworker makes a good point.

if you adjusted your idle mixture with the pcv disconnected and plugged and then added it to the mix you are going to be leaner than you were before, also what pcv valve are you using ? different pcv valves have different metering values.

I too like the ME wagner adjustable pcv valve, also 650 rpm idle speed seems a tad low (by todays standards) unless you have a totally stock engine and I have no clue how the transfer slots work on your particular carb.

Update . . . This worked. I reinstalled the driver side PCV and connected it to the proper (middle) port on the carburetor. The passenger side is a breather for now but I will connect that to the air cleaner tomorrow. I readjusted the idle air screws methodically with a vacuum gauge and it now runs great!

I still have a slight miss when I nail it hard, but that is likely an accelerator pump issue which I will deal with later.

  • Like 1
Link to comment
Share on other sites

Nice!  Glad to hear you are getting it sorted.

It is worth coming up with a tuning kit for the carburetor platform you run.  Takes the frustration out of it when you have all the bits.  
 

My Holley / Demon kit.

 

EB68E248-CEB9-4AE0-8861-694D7FE079A8.jpeg

  • Like 1
Link to comment
Share on other sites

Update . . .

I bought a small hand drill set on Amazon and drilled out the accelerator pump one drill size larger. I have no idea what size that is, the drill bits are tiny. But I inserted the largest bit that I could into the accelerator pump jets, then drilled out to the next size up. It helped! But I think I could go one more size. I'll do that next time I have the carb apart.

To recap . . . here's what I've done to make the Edelbrock 1813 (800CFM) perform well on my 3514V

1. Set air screws as exact as possible using vacuum gauge (with PCV correctly functioning). I have my idle set around 850.

2. Drill out accelerator pump slightly larger.

3. Bend accelerator pump rod slightly to give a larger shot of gas.

4. Set the AVS secondary air flap to 2.25 turns closed (counterclockwise). Factory setting is 1.5 turns. It was opening way too early and leaning out the mixture. Adding 3/4 of a turn solved that. I might even try another 1/4 turn at some point.

5. Changed the rods 2 steps richer. NOTE: I'm not sure if this solved anything and might go back to stock at some point to test.

6. Changed the step up springs to silver (the stiffest ones).

I believe that items 1, 2, 3 and 4 had the largest impact on drivability.

Thanks to everyone for all of their help! 

Edited by 73inNH
Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...