• Hello there guest and Welcome to The #1 Classic Mustang forum!
    To gain full access you must Register. Registration is free and it takes only a few moments to complete.
    Already a member? Login here then!

I need some help

34isgreat

34isgreat

Member
My Mustang is running rough, has everyday I have owned it (2 years). It has the factory six with the autolite 1 barrel carb and a C4 automatic, all stock all factory. I have had carb rebuilt twice now, a complete tune up, new plug wires, coil, distributor cap & rotor. Replaced both fuel filters, symptoms are as follows...
Starts well and runs good at idle, runs good when accelerating but engine has a small skip when held at a steady RPM. Skips when on the road or when in park. Never skips when cold but after engine heats up (say 15 minutes starts to skip and skips more and more the longer you drive. Can start skipping, you mash the gas and it stops as long as you are accelerating, as soon as you hold at steady RPM runs rough???

Anyone, what would you look at to correct this???
 
No just the factory gauge, I have a new radiator and a 190 degree thermostat, gauge runs on the low side of normal operating zone. I do not have a over heating issue. This is driving me nuts!
 
Remove the carbs top and check for particals in fuel bowl.
Sounds like it lacks constant fuel flow thru jet at speed.
 
More info, car runs good at low RPM, I have no tach but under 35 MPH car runs good. Over 35 car starts to run rough and the faster you go the worse it gets.
 
Sure sounds like it is starving for fuel. If things are clean and clear of junk, I'd lean toward low fuel pressure from the pump.
 
"34isgreat" said:
More info, car runs good at low RPM, I have no tach but under 35 MPH car runs good. Over 35 car starts to run rough and the faster you go the worse it gets.
Click to expand...

Fuel hose collapsing ??
 
Disconnect the vacuum hose from the distributor and try driving it again and tell me what happens.

Mel
 
"guruatbol" said:
Disconnect the vacuum hose from the distributor and try driving it again and tell me what happens.

Mel
Click to expand...
Disconnected the vacuum, no improvement. What are your thoughts?
 
More info please...

Are you still running points? Original dizzy? The 65/66 and 67 are different. Sometimes people put the 65/66 in a 67 and visa versa.

What 1 barrel carb do you have? Autolite 1100? Same goes for the carb. Since they are interchangeable people put on the wrong one.
The dizzy and carb should be matched.

Here is more info on the carbs/dizzy combo: http://www.classicinlines.com/CarbChoice.asp

There is a vacuum port on the spacer. Is it clean? Was the correct gasket used on the carb for the vacuum port to operate correctly?





No vacuum leaks??

If all of the above is correct. The fuel pump is an easy and cheap swap.
 
OK, the 200 straight six has a cast iron intake that is part of the head. After time they get pin holes in them which causes vacuum leaks which will cause among other things rough running. I am a bit puzzled about it running fine below 35 MPH. I do wish you had a tach.

You can try starting the car, then with the air cleaner and housing on spray carb cleaner on the intake. If the engine changes rpm pitch or idles rougher or dies you have pin holes in your intake.

You can do a quick fix for this by painting the intake with an epoxy paint!

The other thing could be the fuel is boiling. You could insulate your fuel line near heat sources. or swap the fuel pump out or both.

Those are the only two things I can think of given the symptoms.

Mel
 
"65coupei6" said:
More info please...

Are you still running points? Original dizzy? The 65/66 and 67 are different. Sometimes people put the 65/66 in a 67 and visa versa.

What 1 barrel carb do you have? Autolite 1100? Same goes for the carb. Since they are interchangeable people put on the wrong one.
The dizzy and carb should be matched.

Here is more info on the carbs/dizzy combo: http://www.classicinlines.com/CarbChoice.asp

There is a vacuum port on the spacer. Is it clean? Was the correct gasket used on the carb for the vacuum port to operate correctly?





No vacuum leaks??

If all of the above is correct. The fuel pump is an easy and cheap swap.
Click to expand...
Thanks I will look at this today, good tip.
 
"guruatbol" said:
OK, the 200 straight six has a cast iron intake that is part of the head. After time they get pin holes in them which causes vacuum leaks which will cause among other things rough running. I am a bit puzzled about it running fine below 35 MPH. I do wish you had a tach.

You can try starting the car, then with the air cleaner and housing on spray carb cleaner on the intake. If the engine changes rpm pitch or idles rougher or dies you have pin holes in your intake.

You can do a quick fix for this by painting the intake with an epoxy paint!

The other thing could be the fuel is boiling. You could insulate your fuel line near heat sources. or swap the fuel pump out or both.

Those are the only two things I can think of given the symptoms.

Mel
Click to expand...
Thanks Mel, I have wondered about boiling fuel, problem gets worse when engine heats up. Fuel line is factory steel line, runs from fuel pump up side of block and wraps around front of valve cover and enters front of carb. I suppose a vacuum leak could also get worse when engine heats up. I will try the carb cleaner trick and let you know what I find. Can I check the vacuum with a gauge, what do I look for? Thanks for the help. Bill
 
OK took Mel's advise, sprayed intake with carb cleaner with car running, noticed no change in engine RPM's. I have replaced the vacuum can thing on the side of the distributor and checked the vacuum tube between the carb and distributor.
 
Insulate you fuel line. You can also insulate your carb bowl too. Paint the intake to insulate further if needed.

My 200 was awesome but my FIL had a comet that had same issues as you. IIRC we wrapped the fuel lines and painted the intake replaced points and condenser and the issue went away.

I think something under there is getting hot.

Mel

Sent from my DROID RAZR HD using Tapatalk 2
 
A quick way to tell if it's vapor lock is to put several wooden cloth pins on the line. An old trick used regularly on the older cars. If it goes away then you can put better insulation on it.
 
You must log in or register to reply here.
Back
Top