72 misfiring, help please
09-29-2005, 11:30 PM
#1
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Posts: 79
72 misfiring, help please
OK, I know I have posted a long drawn out detail of everything I have done to my car, but I am going to ask for help again.
We have done just about everything we can think of to get her to stop backfiring (popping) while we try to set the timing. Nothing is working. We have rechecked the points, carb, wires and plugs. We have set her at just about every interval below 10. She is still hesitating. Through first, second and into third she loses power and acts like she is running out of gas, but obviously she isn't. At top speed it is less noticeable, but still there.
What do we do now? Should we put in an electronic ignition? Check the vaccuum lines and compression? I am really at my wits end and need some help....please...
Charity
We have done just about everything we can think of to get her to stop backfiring (popping) while we try to set the timing. Nothing is working. We have rechecked the points, carb, wires and plugs. We have set her at just about every interval below 10. She is still hesitating. Through first, second and into third she loses power and acts like she is running out of gas, but obviously she isn't. At top speed it is less noticeable, but still there.
What do we do now? Should we put in an electronic ignition? Check the vaccuum lines and compression? I am really at my wits end and need some help....please...
Charity
09-30-2005, 10:34 AM
#4
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Join Date: Feb 2005
Posts: 120
RE: 72 misfiring, help please
I haven't read what you've done to the car so bear with me...
I'd check to make sure you have no vacuum leaks first, and then make sure the float is set on the carb. Does the car run hot? If so, then it's probably a fuel issue not a timing one. When did this start happening? What did you change, or what event led to this condition? If you're just finishing a motor rebuild then obvoiusly it's going to be a little more difficult to troubleshoot.
As far as looking for a vacuum leak, what I normally do is either run the motor and spray carb cleaner around all the possible areas (carb base, line ends, along intake manifold). If it starts running better when you hit a certain spot, then you found the leak. A little more involving method, which I like better, is to block off the carb so air can't come out the top (rags in the barrels) and then hook up an air line to one of the vacuum lines (5-10psi). Then spray soap water on the motor like you'd do to find a leak in a tire.
As for checking the float level, make sure it's opening and closing the pintle valve within the proper range. That's all I can help you with there because I'm totally clueless and lame with tuning carbs. Hope this helps!
I'd check to make sure you have no vacuum leaks first, and then make sure the float is set on the carb. Does the car run hot? If so, then it's probably a fuel issue not a timing one. When did this start happening? What did you change, or what event led to this condition? If you're just finishing a motor rebuild then obvoiusly it's going to be a little more difficult to troubleshoot.
As far as looking for a vacuum leak, what I normally do is either run the motor and spray carb cleaner around all the possible areas (carb base, line ends, along intake manifold). If it starts running better when you hit a certain spot, then you found the leak. A little more involving method, which I like better, is to block off the carb so air can't come out the top (rags in the barrels) and then hook up an air line to one of the vacuum lines (5-10psi). Then spray soap water on the motor like you'd do to find a leak in a tire.
As for checking the float level, make sure it's opening and closing the pintle valve within the proper range. That's all I can help you with there because I'm totally clueless and lame with tuning carbs. Hope this helps!
09-30-2005, 12:22 PM
#5
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RE: 72 misfiring, help please
Charity,
Just for grins, go back and check the firing order. I forgot which motor yo have, so here is the order for the 302 and the 351.
302- 15425378
351- 13726548
Start at 1:00 o'clock on top of the dizzy for #1 and go counter clockwise for all the others. I bet you will find two out of place.
If you need help, give us a holler.
Just for grins, go back and check the firing order. I forgot which motor yo have, so here is the order for the 302 and the 351.
302- 15425378
351- 13726548
Start at 1:00 o'clock on top of the dizzy for #1 and go counter clockwise for all the others. I bet you will find two out of place.
If you need help, give us a holler.
09-30-2005, 01:38 PM
#6
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Join Date: Sep 2005
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Posts: 79
RE: 72 misfiring, help please
Thanks Guys,
We welcome any advice at all. The hubby has checked the timing order a couple of times and keeps saying it's right, I will check them myself when I get home at 12.
The compression thing, I will have to get a gauge, all the autopart stores around here have nothing to loan so I will have to purchase one.
The vaccuum lines...we tried to set them according to the diagram in the CHilton but there is always something extra in the diagram that we don't have so we are doing the best we can. We did notice that one line from the switch to the distributor has no pressure at all, is that normal? We, too, have no idea about vaccuum lines and everyone we have talked to says they are a PITA.
Thanks again everyone, I will check the firing order and get back to ya ltr,
Charity
We welcome any advice at all. The hubby has checked the timing order a couple of times and keeps saying it's right, I will check them myself when I get home at 12.
The compression thing, I will have to get a gauge, all the autopart stores around here have nothing to loan so I will have to purchase one.
The vaccuum lines...we tried to set them according to the diagram in the CHilton but there is always something extra in the diagram that we don't have so we are doing the best we can. We did notice that one line from the switch to the distributor has no pressure at all, is that normal? We, too, have no idea about vaccuum lines and everyone we have talked to says they are a PITA.
Thanks again everyone, I will check the firing order and get back to ya ltr,
Charity
09-30-2005, 02:56 PM
#7
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RE: 72 misfiring, help please
Let's make sure we have our terminology straight. Is it backfiring or misfiring? Backfiring will get black smoke coming out of the tailpipe, and is generally a case where the fuel is not completely burned and collects in the exhaust system and explodes there. It is really a misnomer term. Or, is it firing out of the carburetor? Misfiring occurs when the spark plug doesn't fire for whatever reason. It could be bad timing, bad plug wires, bad intake/exhaust valve, cruddy plug tips, etc. So which is it?
If all the suggestions we have made doesn't get it running smoothly, then I would pull the distributor and make sure all the teeth on the gear are in good shape. I understand that you replaced the timing chain. If so, then if it was mine, I would pull the heads and take them to a machine shop to have them rebuilt, or buy a new set of aluminum performance heads and install those. But, before you do anything that drastic, take it the local Ford house and have a qualified Ford Mechanic inspect it. It is or should be quite obvious except for a few on here, that we are shade-tree mechanics.
If all the suggestions we have made doesn't get it running smoothly, then I would pull the distributor and make sure all the teeth on the gear are in good shape. I understand that you replaced the timing chain. If so, then if it was mine, I would pull the heads and take them to a machine shop to have them rebuilt, or buy a new set of aluminum performance heads and install those. But, before you do anything that drastic, take it the local Ford house and have a qualified Ford Mechanic inspect it. It is or should be quite obvious except for a few on here, that we are shade-tree mechanics.
09-30-2005, 04:26 PM
#9
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Join Date: May 2005
Location: Tyler, TX
Posts: 508
RE: 72 misfiring, help please
ORIGINAL: newownerof72
We did notice that one line from the switch to the distributor has no pressure at all, is that normal?
We did notice that one line from the switch to the distributor has no pressure at all, is that normal?
There should be a line coming from your a ported vacuum outlet on your carburetor to your distributor. At Idle, it should be almost nothing, and when you accelerate, it should go up.
09-30-2005, 04:47 PM
#10
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RE: 72 misfiring, help please
ORIGINAL: nualln
What switch?
There should be a line coming from your a ported vacuum outlet on your carburetor to your distributor. At Idle, it should be almost nothing, and when you accelerate, it should go up.
ORIGINAL: newownerof72
We did notice that one line from the switch to the distributor has no pressure at all, is that normal?
We did notice that one line from the switch to the distributor has no pressure at all, is that normal?
There should be a line coming from your a ported vacuum outlet on your carburetor to your distributor. At Idle, it should be almost nothing, and when you accelerate, it should go up.