when I start my 351m I have to keep my foot on the gas at about 2000 2200 rpm for about 2 or 3 min or it will stall also even after I drive it for bit and put it in revere it will stall does anyone no what might be causing this.

 

Check for vacuum leaks. Look for cracked or disconnected hoses.

Get a vacuum gauge and measure the vacuum at idle when it does idle.

Is the idle rough when it does idle?

 

yes the idle is rough and I have pluged up all vacuum lines?

 

Remote troubleshooting is pretty difficult. Please give more details. Otherwise, you'll just get a bunch of WAGs.

Is the engine completely stock, or modified? If modified, exactly how (what non-stock components or configuration)?

Do you have a manual or automatic transmission?

Have you made any recent changes to the engine? Done any recent maintenance? Replaced any parts? Do you know whether the engine is tuned to factory specs (i.e., timing, etc.)?

What do you mean when you say you have plugged up all vacuum lines? Are all your vacuum systems disabled?

It would also help if you could describe the symptoms in more detail.

Does the engine always stall when it is warmed up? When does it not stall? Does the idle ever smooth out?

Does it ever run "right" under any conditions? If so, what conditions?

What do you have to do to get the engine to restart? Do you have to hold the throttle wide open, or does it fire right up with only a slight touch on the accelerator pedal?

Does any smoke come out the tail pipe? Do you smell unburnt fuel in the exhaust when it's acting up?

Do any weather conditions affect the problem (e.g., cold or wet or dry or hot)?

Finally, have you done anything to troubleshoot the problem yourself? If so, what did you find out?

No problem if you're not an expert, but you gotta give the people here more info if you want effective help.

 

well the engine is stock the tran is automatic. when I start it up I have to give it a couple pumps then hold it at about half way to the floor, then I have to hold the petal at about 2000 rpm for about 2min befor it idles on it's own and even then it is very ruff. bought this bronco like this I have tryed advancing the timeing and there is no change the rpms don't even come up that high. I have all so played around with the idle by turning it in but thats does'nt seem to help. it does'nt smoke and it has been pretty hot here latey, when your at a stop it feels like it's going to stall and it does if you are there to long sometimes when you pull out on the hwy and give it a little gas it coughs and chugs but when thats over it has loads of power.

 

What is the mileage or mileage since the last overhaul? I would recommend a compression test, look for a difference between cylinders, and also reading the manifold vacuum, look for jumping vacuum.
Is there valve noise?
Are the valves adjusted correctly? (0 lash).

 

Sounds to me like the choke pull-off. When the engine is cold, it should take one pump of the throttle to "set" the choke, that is, the choke plate should snap closed. If the outside temp is very warm, the choke should just barely close. (It might be set too tight.)
Then when you first start it, the choke pull-off diaphragm opens the choke plate just a little bit to keep the engine from loading up. (The symptoms you're having.) There is a specific amount the choke should open, check the specs for your carb. Should be just over an eighth of an inch.
As the engine warms up, there is an electric heater in the choke housing (the round black "can" on the side of the carb with the wire going to it) that warms the bimetal spring that closed the choke. The choke should gradually open and should be fully open just before the engine reaches operating temp. The electric heater gets its power from the stator terminal of the alternator. If the electric heater isn't working, the choke will still open from the engine heat but it takes too long and runs too rich until it fully opens.
Sometimes the heater in the choke housing burns out and the choke housing needs to be replaced.
Sometimes the choke pull-off diaphragm gets a leak and won't open the choke just that little bit it needs to keep the engine from loading up when first starting.

To see what's happening, pull the top of the air cleaner off and lay it to the side without disconnecting the vacuum lines for the warm air door, (a good thing to keep). Start the engine and watch the choke. After the initial bump open, it should completely open in a couple of minutes at the most, this time of year. If it doesn't, try loosening the three screws that hold the choke housing and rotating it until it does. If it doesn't bump open, replace the choke pull-off.
Hope this helps.
Greg

 

greg thanks for the great advice I'm going to try that today and let you know whats happening. thanks again.

 

The M engines had a number of different choke configurations. Some were electric, some were hot air, some were a combination of both. There are areas that can be troublesome in these things.

One of the most common configurations is a "looped" hot air system where a vacuum is drawn from the air horn of the carb (rubber hose to metal pipe), then it runs through a looped heater stove next to the carb on the manifold. Finally, the heated air goes through a metal hose that threads into the choke unit. Often, the inlet from the air horn comes out of where it joins to the manifold stove...its just pressed in metal pipe. Check this first, then check to be sure your vacuum from the carb is still connected. You need both to operate this kind of choke unit.

Obviously, if the choke has an electrical clip, check for 12 volts on the wire.

Lastly, sometimes the center manifold ports on boths sides of the carb, that draw from exhaust gases leaving the heads, can get clogged with carbon deposits (often from "cheap" gas) that seem as hard as rock. Some 351 and 400's also draw vacuum for the PCV or EGR from a manifold port the opposite side of the choke, which is small and easily clogged. This will cause a boatload of running and idle problems.

You have to pull off the intake manifold and spray, scrape, and pick until the ports are cleared, then blow the whole manifold out with compressed air to blow out the junk.