Fuel System Problems - 351 M 2 bbl
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Fuel System Problems - 351 M 2 bbl
I have a '84 F150 4x4, 351M with a 2 barrel carb. The last couple of weeks it has been running very bad. It starts OK, but when when its coming up to operating temperature, it starts missing, cutting out, etc.
I replaced the plugs, wires, dist cap, and rotor button. Didn't help. Took it to my mechanic buddy, he traced down some vacumm leaks, and loose connection on one plug wire. Didn't help - so he said that I have a fuel problem, most likely water in fuel.
So, this past weekend, carried all my fuel cans in trunk of Maxima and filled with 93 Octane fuel. Put 12 gallons in the front tank of my truck along with half a bottle of Octane boost. Let truck run 30 minutes at idle, (with frequent re-starts required) - still missing and cutting out. Then I sat in truck holding throttle at 2000 rpm for another 20 minutes - still didn't help.
What's wrong with it? I've got a fishing trip coming up this next week, and I don't think the Maxima will pull my boat.
Thanks in advance for any ideas that would make my life a little less complicated.
I replaced the plugs, wires, dist cap, and rotor button. Didn't help. Took it to my mechanic buddy, he traced down some vacumm leaks, and loose connection on one plug wire. Didn't help - so he said that I have a fuel problem, most likely water in fuel.
So, this past weekend, carried all my fuel cans in trunk of Maxima and filled with 93 Octane fuel. Put 12 gallons in the front tank of my truck along with half a bottle of Octane boost. Let truck run 30 minutes at idle, (with frequent re-starts required) - still missing and cutting out. Then I sat in truck holding throttle at 2000 rpm for another 20 minutes - still didn't help.
What's wrong with it? I've got a fishing trip coming up this next week, and I don't think the Maxima will pull my boat.
Thanks in advance for any ideas that would make my life a little less complicated.
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From: Minneapolis, MN
Fuel System Problems - 351 M 2 bbl
Does it seem to be running rich or lean? Could be crud in the carb or a sunk float. Did your mechanic put it on a scope? Adjust the idle mixture? Do a compression test? Have you replaced the PCV valve?
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Fuel System Problems - 351 M 2 bbl
Here's the latest. Carb removed and soaked for half day in cleaner. Fresh fuel filter and carb Kit installed and carb placed on truck last night.
After finally getting fuel up to the carb it ran very rich (black smoke) and wouldn't idle. Started tweaking the idle mixture screws and continually restarting the truck. Seemed to help for a little while, but then I started trying to adjust the choke - made things worse.
Then noticed that a lot of gas seemed to be coming between the air cleaner housing and the carb. Figured the float was too high, so I removed top part of carb and bent the float thingy a little (according to kit instructions) to lower level.
To make a long story short - Never did get the black smoke to stop, nor get it to idle, now it won't even start (turns over but just won't go).
Would a new carb, and manual choke be in my not so distant future?
After finally getting fuel up to the carb it ran very rich (black smoke) and wouldn't idle. Started tweaking the idle mixture screws and continually restarting the truck. Seemed to help for a little while, but then I started trying to adjust the choke - made things worse.
Then noticed that a lot of gas seemed to be coming between the air cleaner housing and the carb. Figured the float was too high, so I removed top part of carb and bent the float thingy a little (according to kit instructions) to lower level.
To make a long story short - Never did get the black smoke to stop, nor get it to idle, now it won't even start (turns over but just won't go).
Would a new carb, and manual choke be in my not so distant future?
Last edited by hvfd751; Jun 3, 2003 at 06:37 AM.
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Fuel System Problems - 351 M 2 bbl
No. I haven't changed the float. It wasn't included in the kit.
Neither were the idle mixture screws which had an asterisks by them in the instructions noting that some kits included new screws.
Doesn't seem to be fuel pump or filter - carb has a lot of fuel in it.
Float? Well it was floating, and when pushed down it popped back up. As stated earlier, I bent the thingy a little to lower the fuel level - may have gone to far though, but I didn't move it much.
Needle valve and seat? New ones installed.
There was one item in the kit that did not resemble the one on my carb - the power valve. Actually the one included in the kit wouldn't even seat in its proper location, so I used my old one.
Anybody interested in buying a used '84 F150 4x4 Ext cab long bed, 351M (1.# barrel carb:-) )?
Neither were the idle mixture screws which had an asterisks by them in the instructions noting that some kits included new screws.
Doesn't seem to be fuel pump or filter - carb has a lot of fuel in it.
Float? Well it was floating, and when pushed down it popped back up. As stated earlier, I bent the thingy a little to lower the fuel level - may have gone to far though, but I didn't move it much.
Needle valve and seat? New ones installed.
There was one item in the kit that did not resemble the one on my carb - the power valve. Actually the one included in the kit wouldn't even seat in its proper location, so I used my old one.
Anybody interested in buying a used '84 F150 4x4 Ext cab long bed, 351M (1.# barrel carb:-) )?
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Fuel System Problems - 351 M 2 bbl
There is a little wire clip that hooks on both ends of the float pivot pin. The curved middle of that clip must be pushed down (between the wall of the bowl and the inlet valve seat) to engage the groove around the outside of the inlet valve seat. That holds the float in position.
Without that clip securing the pivot pin, the float will not push the needle valve against its seat to cut off fuel flow from the pump, and you will have massive flooding out the main bowl vents on top of the carb.
Power valves may have slightly different designs for the side exposed to vacuum, but they are interchangeable. Some 2150 carbs have a small power valve cover with no external vacuum port, and some two-stage power valves will not fit inside them.
For initial adjustment of the idle mixture needles, try turning them all the way in, then back out (counter-clockwise) 2 turns. Once you get the engine running, adjust the idle mixture needles to get the highest manifold vacuum with the engine running smoothly at the correct idle speed.
Without that clip securing the pivot pin, the float will not push the needle valve against its seat to cut off fuel flow from the pump, and you will have massive flooding out the main bowl vents on top of the carb.
Power valves may have slightly different designs for the side exposed to vacuum, but they are interchangeable. Some 2150 carbs have a small power valve cover with no external vacuum port, and some two-stage power valves will not fit inside them.
For initial adjustment of the idle mixture needles, try turning them all the way in, then back out (counter-clockwise) 2 turns. Once you get the engine running, adjust the idle mixture needles to get the highest manifold vacuum with the engine running smoothly at the correct idle speed.
Last edited by bubbaf250; Jun 3, 2003 at 01:23 PM.
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Fuel System Problems - 351 M 2 bbl
Quote: There is a little wire clip that hooks on both ends of the float pivot pin. The curved middle of that clip must be pushed down (between the wall of the bowl and the inlet valve seat) to engage the groove around the outside of the inlet valve seat. That holds the float in position.
Yeah, I remember that thing.
Quote: Without that clip securing the pivot pin, the float will not push the needle valve against its seat to cut off fuel flow from the pump, and you will have massive flooding out the main bowl vents on top of the carb.
Sounds exactly like what is happening. I did notice that the pivot pin seemed to move around alot. But I'm not exaclty sure how it should be.
When you say "between the wall of the bowl", do you mean the wall of the carb bowl opposite side of the valve seat from the float?
So it would be in this order going from left to right:
carb bowl wall / curved clip / valve seat / float
Yeah, I remember that thing.
Quote: Without that clip securing the pivot pin, the float will not push the needle valve against its seat to cut off fuel flow from the pump, and you will have massive flooding out the main bowl vents on top of the carb.
Sounds exactly like what is happening. I did notice that the pivot pin seemed to move around alot. But I'm not exaclty sure how it should be.
When you say "between the wall of the bowl", do you mean the wall of the carb bowl opposite side of the valve seat from the float?
So it would be in this order going from left to right:
carb bowl wall / curved clip / valve seat / float
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Fuel System Problems - 351 M 2 bbl
Got the float thing fixed, fuel level in bowl seems to be OK now.
Yesterday morning, truck started right up, idled good, no black smoke. Revved up smooth, and idled back down smooth.
So I'm thinking, OK, this is good, I'll be fishing this weekend.
Go for a test drive, but carry cell phone just in case.
Make it about two miles, and truck starts cutting out, and puffing black smoke. This happens at the same time as it reaches operating temperature (point at which the thermostat opens, I assume). This is exactly how/when the original problem that caused me to rebuild the carb started.
I'm thinking it has something to do with the thermo sensor on top of the thermostat housing. Wire seems to be intact, but the vacuum lines are being attacked by a small gremlin, that likes to remove them.
Is the thermo sensor possibly sending a signal to the electric choke, telling it to do something when the thermostat warms up?
Could I test this by disconnecting the choke pull down from the carb?
Any ideas on this would be greatly appreciated. My father-in-law is getting tired of me borrowing his truck.
Yesterday morning, truck started right up, idled good, no black smoke. Revved up smooth, and idled back down smooth.
So I'm thinking, OK, this is good, I'll be fishing this weekend.
Go for a test drive, but carry cell phone just in case.
Make it about two miles, and truck starts cutting out, and puffing black smoke. This happens at the same time as it reaches operating temperature (point at which the thermostat opens, I assume). This is exactly how/when the original problem that caused me to rebuild the carb started.
I'm thinking it has something to do with the thermo sensor on top of the thermostat housing. Wire seems to be intact, but the vacuum lines are being attacked by a small gremlin, that likes to remove them.
Is the thermo sensor possibly sending a signal to the electric choke, telling it to do something when the thermostat warms up?
Could I test this by disconnecting the choke pull down from the carb?
Any ideas on this would be greatly appreciated. My father-in-law is getting tired of me borrowing his truck.
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From: Minneapolis, MN
Fuel System Problems - 351 M 2 bbl
Just a thought... Could the TVS to the EGR valve be switching on to manifold vacuum when the temp warms up making the EGR valve open more than it should?
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From: (near) Denver USA
Fuel System Problems - 351 M 2 bbl
Engine temp sensors have nothing to do with the choke. The choke has its own thermostat. If the engine runs well cold, and it has problems cutting out with black smoke when warm, it's not likely the choke, perhaps not even the carb.
Does your truck use the DuraSpark II ignition system? If so, check the magnetic pickup inside the distributor. Sometimes the permanent magnet cracks, and it causes problems only when the engine warms up and the crack expands.
Do you know where the 351M engine in your truck came from? It's not original in that vehicle.
If the vacuum systems are not set up correctly, which requires having the correct calibration label for your engine, you could have EGR problems like macguyver suggested or other problems.
Count the number of bolts holding down the valve covers. If you don't have 8 bolts, the engine is not a 351M. I suspect your engine is a 351 Windsor, and you might be able to get more specific advice on the Windsor V8 forum.
Does your truck use the DuraSpark II ignition system? If so, check the magnetic pickup inside the distributor. Sometimes the permanent magnet cracks, and it causes problems only when the engine warms up and the crack expands.
Do you know where the 351M engine in your truck came from? It's not original in that vehicle.
If the vacuum systems are not set up correctly, which requires having the correct calibration label for your engine, you could have EGR problems like macguyver suggested or other problems.
Count the number of bolts holding down the valve covers. If you don't have 8 bolts, the engine is not a 351M. I suspect your engine is a 351 Windsor, and you might be able to get more specific advice on the Windsor V8 forum.
