1973 Mustang Mach 1 351 Cleveland Sputtering and Hesitating at acceleration

[salhi_aemr]

Hello all,

I am wondering if someone can help. My 73 Mach 1 with 351 Cleveland is sputtering and hesitating at acceleration especially hard acceleration and at beginning of driving it at low speed. It looks like its starving for gas but I am not sure. I changed Fuel Filter and my car is recently rebuild and there is no vacuum leak. Also I hear fuel pump working. I have HOLLEY 600 CFM CARBURETOR 80457-8 4 BBL on it since they changed the intake to take 4 Barrel carbs. Its driving me crazy. Could it be the MSD Ignition coil or timing. All help is appreciated. Thank ya'll.


the car idles fine and there is no hesitation and it fires right away. When I take off air cleaner and look at inside carb and i give gas, I see gas going inside the carb fine.

 

[will e]

These kinds of issues are always hard to diagnose over the internet. You are about to receive a lot of advice on what it is and what to swap out.

But first a few more questions.

You mention fuel filter, recently rebuilt and some info on changing it to a holley 600 cfm and an intake to work with 4bl carbs.

So, was the car running okay and it started having issues or has it had these issues since the rebuild and change over to 4bbl and intake.

What kind of intake do you have now (brand and type). What was on it before? Was it a stock 2bbl with a stock for 2bbl intake?

How does it run at a constant speed? Does it seem to run okay?

I hate to start off with something to check before knowing more info but have you confirmed that the firing order is correct?

The front passenger cyl is number one.

Front

5 1

6 2

7 3

8 4

rear

Above is the numbers for the cyls.

The firing order is 1 3 7 2 6 5 4 8

The important part is that they are in the correct order, not in the exact position on the distributor shown in the pic.

So confirm this first. Start with #1 and trace the wires to each cyl and confirm they are in the correct position. Please answer the above questions and with the additional information we can suggest additional step.

BTW, do you have a vacuum gauge? If no, please buy a one at the local auto store. They are inexpensive and invaluable to trouble shooting issues.

 

[salhi_aemr]

Thank you Will, I will get all the answers for you tomorrow, but I will def check the firing sequence tomorrow as well

 

[jb73Mach]

When was the last time you changed the plugs? Check for carbon and check the gap. It could be as simple as that (I know after serious hesitation but starting like a dream). Kicked myself for not checking the easy stuff first.

 

[jbojo]

Just to add, do you know what the ignition timing is?

 

[cudak888]

If your base timing, vacuum advance, and plugs check out, take a look at the accelerator pump cam on the throttle shaft of your Holley.

I once put a 600cfm 4160 on top of a 400 and didn't check the cam - turns out it was one of the small cams, and the cam was timed to give the pump shot at the wrong time. Thus, a bog on acceleration from a stop and hard acceleration from a rolling start. I installed a larger cam and the problem was taken care of away.

-Kurt

 

[ceheler]

I agree with Mr. Will in what he said. More info will help a lot beings as we cannot see the car and get our hands on it. Another thing to try that is easy and fast that is a common wear item is plug wires. Easy to do with a spray bottle and some water. Mist the spark plug wires with water and start the engine preferably in a shaded area then look for the pretty blue arc to form between the plug wire and a ground. I will follow the post ad provide whatever help i can.

 

[salhi_aemr]

Well all I bring car to shop to check on it and change my plugs and wires too and after diagnostic it turned out I had a bad carburator after all. The power valve in it was bad. It's a Holley 80457-S and its old. Am under three options. Rebuilding it, get another new Holley just like the one I have, or go with Edlerbrock 1406. I am leaning more toward the Elderbrock since its a street car I am not racing it. What do you guys recommend. Also the Elderbrock is easy to install I would do it myself and it requires low tuning. Also any tips on how to take off my old Holley and put the new one or it should be easy, never done it. Thanks a lot

View attachment 24910

 

[mjlan]

Welcome to Holley carbs!

It's not that difficult to change a power valve. Why not just replace it and see if that fixes your problem? It is also easy (but not tasty) to check the old one once you have it out by sucking on it... It's located in the primary metering block (side of the carb closest to the radiator) between the fuel bowl and main body. You can get to it by removing the four long bowl screws and the transfer tube. Most local auto parts stores will have power valves and the necessary gaskets, or you could pick up a kit that contains all of the parts. Watch out for the transfer tube- it's sealed with O-rings and they are a pain in the *** to get situated. Also, might be easier to pull the carb off of the motor for this...

 

[salhi_aemr]

Thank you Mjlan, but when I got car last year there was gas drops leak in power valve once car is fired. The mechanic ( did a crappy job ) did change the power valve with a rebuild kit I got him from Pepboys. But recently it went out again, am

thinking the whole carb is dirty and not clean and it's pretty old and sat a while so I would think getting a new fresh one is a better idea. What do you think?

 

[mjlan]

That's interesting that the you are having the same issue again.

Does the car backfire through the carb? Older Holleys didn't have protection for the PV, and if a backfire happened it would rupture the PV diaphragm.

The repair or replace question is up to you- are you more confident in being able to figure out what's happening with your current carb, or would you rather start with a new one? Holleys require some tweaking to get dialed in.

It might be worth finding a reputable shop with a dyno and pay them to tune and adjust the carb for you. I would think that there's probably a few good Holley tuners in the Houston area?

 

[salhi_aemr]

Do you happen to know any shops here?

 

[will e]

If you believe it is the power valve I would try replacing the power valve. Get a genuine holley.

A simple test is to get your car to normal operating temperature. Close the idle screws (count the number of turns so you can put them back). To close them turn the clockwise. You most likely won't have to turn them more than an couple of turns. If you close the idle screws and the engine dies, you do not have a bad power valve.

Lots of good information here:

http://forums.holley.com/entry.php?430-Holley-Power-Valve-Tuning

 

[salhi_aemr]

Thank You Will, amma go try it later on today

 

[salhi_aemr]

Well i just realized I have a gift card from Summit Racing that I haven't used and it came in handy and in Christmas time, I bought Holley 0-80457SA brand new. Looking forward to install it and will write my review after.

View attachment 24920

 

[MustangChris]

saw this and am wondering if you ever resolved the issue. I had the same exact issue I changed eveything and found a really great mechanic who said the issue was torque converter. Might be something to consider especially if you have a FMX transmission

Hello all,

I am wondering if someone can help. My 73 Mach 1 with 351 Cleveland is sputtering and hesitating at acceleration especially hard acceleration and at beginning of driving it at low speed. It looks like its starving for gas but I am not sure. I changed Fuel Filter and my car is recently rebuild and there is no vacuum leak. Also I hear fuel pump working. I have HOLLEY 600 CFM CARBURETOR 80457-8 4 BBL on it since they changed the intake to take 4 Barrel carbs. Its driving me crazy. Could it be the MSD Ignition coil or timing. All help is appreciated. Thank ya'll.


the car idles fine and there is no hesitation and it fires right away. When I take off air cleaner and look at inside carb and i give gas, I see gas going inside the carb fine.