'78 351M Choke adjust?
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Fleet Mechanic
Joined: Feb 2001
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From: Toronto, Canada
'78 351M Choke adjust?
I have had the mixture and timing adjusted and runs great, except, sometimes, the choke comes on and you cannot 'kick' it down. How do I adjust this? (manuals are too complicated for me)
As well, I believe that when the motor is turned off when the choke is engaged, it 'diesels'. As well, it knocks when you restart it after the dieseling condition.
HELP!
Thanks!
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1978 F250 4x4 - 351M
Don't crush them, restore them!
As well, I believe that when the motor is turned off when the choke is engaged, it 'diesels'. As well, it knocks when you restart it after the dieseling condition.
HELP!
Thanks!
https://www.ford-trucks.com/dcforum/User_files/3ae0a7e34062b4ad.jpg https://www.ford-trucks.com/dcforum/User_files/3ae0a7b33fe32dbb.jpg
1978 F250 4x4 - 351M
Don't crush them, restore them!
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From: Virginia
'78 351M Choke adjust?
There is a large black round housing on the passenger side of the carb. It should say rich-lean on it with arrows. Loosen the three screws and turn this housing to adjust. Sometimes instead of screws there will be pop rivets. These will have to be drilled out and screws installed before it can be adjusted. If after adjustment, you have no choke at all, the element in the black housing might be burnt out.
Thread Starter
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Fleet Mechanic
Joined: Feb 2001
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From: Toronto, Canada
'78 351M Choke adjust?
I assume that I lean it out?
Isn't this just a mixture adjustment, not choke?
Thanks!
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1978 F250 4x4 - 351M
Don't crush them, restore them!
Isn't this just a mixture adjustment, not choke?
Thanks!
https://www.ford-trucks.com/dcforum/User_files/3ae0a7e34062b4ad.jpg https://www.ford-trucks.com/dcforum/User_files/3ae0a7b33fe32dbb.jpg
1978 F250 4x4 - 351M
Don't crush them, restore them!
Laughing Gas
Joined: Dec 2000
Posts: 781
Likes: 18
From: East Texas
'78 351M Choke adjust?
This may not be a choke problem as much as a problem with the electric throttle position solenoid (don't remember the exact name off hand). This is on the driver's side and holds the throttle linkage at a certain position at idle. If it holds the linkage too high, this can seem like the carburetor is on the fast idle cam. It also can cause the dieseling on shutdown. It is mounted on a bracket and can be adjusted along the bracket if I remember correctly. It's just been a while since I changed and adjusted the one on my truck. Hope this may help a little.
Jason
1993 F-150 300 I-6/5-Spd.
1977 F-250 351M/4-Spd.
Jason
1993 F-150 300 I-6/5-Spd.
1977 F-250 351M/4-Spd.
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Joined: Apr 2001
Posts: 321
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'78 351M Choke adjust?
[font size="1" color="#FF0000"]LAST EDITED ON 31-May-01 AT 02:25 PM (EST)[/font][p][font size="1" color="#FF0000"]LAST EDITED ON 31-May-01 AT 02:24 PM (EST)[/font]
Hi,
How is the choke housing set up? Does it have the small heat tube that runs from the intake to the bottom of the choke coil? If it does, it may be plugged, or the choke coil can be carboned up. Also, what voltage do you have at the choke coil? It should be around 8 volts.
Are you sure that it is the choke that is coming on, sometimes the "dashpot" that is supposed to slow down the return of the throttle plates becomes stuck/bad, and can cause the throttle to stay open a little. The dashpot is on the right front side of the carb, and is mounted on a little bracket.
Some things to try...
Also, how long after the dieseling sound until you re-start it? If it is off for a while (an hour?), the warm oil will easily run back into the oil pan, and the crank can "knock" for a second unitl the oil pressure builds up. My truck has this same problem.
-Brents
Hi,
How is the choke housing set up? Does it have the small heat tube that runs from the intake to the bottom of the choke coil? If it does, it may be plugged, or the choke coil can be carboned up. Also, what voltage do you have at the choke coil? It should be around 8 volts.
Are you sure that it is the choke that is coming on, sometimes the "dashpot" that is supposed to slow down the return of the throttle plates becomes stuck/bad, and can cause the throttle to stay open a little. The dashpot is on the right front side of the carb, and is mounted on a little bracket.
Some things to try...
Also, how long after the dieseling sound until you re-start it? If it is off for a while (an hour?), the warm oil will easily run back into the oil pan, and the crank can "knock" for a second unitl the oil pressure builds up. My truck has this same problem.
-Brents
Thread Starter
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Fleet Mechanic
Joined: Feb 2001
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Likes: 15
From: Toronto, Canada
'78 351M Choke adjust?
Jason, could this be the dashpot the message below you is referring to??
Matt
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1978 F250 4x4 - 351M
Don't crush them, restore them!
Matt
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1978 F250 4x4 - 351M
Don't crush them, restore them!
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From: Virginia
'78 351M Choke adjust?
The large black housing with rich-lean, is the choke adjustment. And the other posters have valid stuff to look at too. They changed configurations from year to year and with different options (ac/auto trans etc.) but they are talking about something holding the throttle open on the drivers side of the carb. The solenoids I've seen are large round cylindrical units with wire(s) coming out the back and an adjustment bolt on the other end that contacts the throttle linkage on the carb. The dashpots I've seen also contact the throttle linkage, but are flatter looking with no wires and contain a diaphram inside.
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Thread Starter
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Fleet Mechanic
Joined: Feb 2001
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From: Toronto, Canada
'78 351M Choke adjust?
[font size="1" color="#FF0000"]LAST EDITED ON 01-Jun-01 AT 01:07 PM (EST)[/font][p]I have a solenoid - wire going to it, and a plunger on the end to contact the throttle linkage.
OBSERVATIONS- the plunger will not move by pushing with my finger, and does not contact the linkage at idle or at any other rpm.
Does this mean I need a new one?
Shouldn't there be contact at idle?
Finally, what hole should the accelerator pump be in for my 1978 351M with 4 speed?
Mine is in the top hole. It looks to me as if it is in the wrong hole because the hole below the top one looks worn. (I had the engine rebuilt and a chevy guy put it in (don't ask))
Thanks!
https://www.ford-trucks.com/dcforum/User_files/3ae0a7e34062b4ad.jpg https://www.ford-trucks.com/dcforum/User_files/3ae0a7b33fe32dbb.jpg
1978 F250 4x4 - 351M
Don't crush them, restore them!
OBSERVATIONS- the plunger will not move by pushing with my finger, and does not contact the linkage at idle or at any other rpm.
Does this mean I need a new one?
Shouldn't there be contact at idle?
Finally, what hole should the accelerator pump be in for my 1978 351M with 4 speed?
Mine is in the top hole. It looks to me as if it is in the wrong hole because the hole below the top one looks worn. (I had the engine rebuilt and a chevy guy put it in (don't ask))
Thanks!
https://www.ford-trucks.com/dcforum/User_files/3ae0a7e34062b4ad.jpg https://www.ford-trucks.com/dcforum/User_files/3ae0a7b33fe32dbb.jpg
1978 F250 4x4 - 351M
Don't crush them, restore them!
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Thread Starter
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Fleet Mechanic
Joined: Feb 2001
Posts: 1,290
Likes: 15
From: Toronto, Canada
'78 351M Choke adjust?
Is it possible that the accelerator pump linkage is holding the throttle linkage too high and not allowing the linkage to come down to the solenoid?
https://www.ford-trucks.com/dcforum/User_files/3ae0a7e34062b4ad.jpg https://www.ford-trucks.com/dcforum/User_files/3ae0a7b33fe32dbb.jpg
1978 F250 4x4 - 351M
Don't crush them, restore them!
https://www.ford-trucks.com/dcforum/User_files/3ae0a7e34062b4ad.jpg https://www.ford-trucks.com/dcforum/User_files/3ae0a7b33fe32dbb.jpg
1978 F250 4x4 - 351M
Don't crush them, restore them!
Thread Starter
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Fleet Mechanic
Joined: Feb 2001
Posts: 1,290
Likes: 15
From: Toronto, Canada
'78 351M Choke adjust?
In reply to earlier posts, the hard knocking sound occurs even when immediatley restarting the motor.
(I have a newly rebuilt engine too)
https://www.ford-trucks.com/dcforum/User_files/3ae0a7e34062b4ad.jpg https://www.ford-trucks.com/dcforum/User_files/3ae0a7b33fe32dbb.jpg
1978 F250 4x4 - 351M
Don't crush them, restore them!
(I have a newly rebuilt engine too)
https://www.ford-trucks.com/dcforum/User_files/3ae0a7e34062b4ad.jpg https://www.ford-trucks.com/dcforum/User_files/3ae0a7b33fe32dbb.jpg
1978 F250 4x4 - 351M
Don't crush them, restore them!
Laughing Gas
Joined: Dec 2000
Posts: 781
Likes: 18
From: East Texas
'78 351M Choke adjust?
weldman,
It is the dashpot device also referred to. It does have a wire running to it. If the plunger doesn't move anytime, you could need a new one. I had to replace the one on my truck a few years ago, and know when I was adjusting the new one, I had it set originally so that it was holding the linkage a little too far open, and it sounded like the engine was on fast idle and when I tried to shut it off, it dieseled.
As I recall, it wasn't too expensive so you might give this a try. Sorry I don't remember the exact name, it's just been several years since I had to purchase one.
Jason
1993 F-150 300 I-6/5-Spd.
1977 F-250 351M/4-Spd.
It is the dashpot device also referred to. It does have a wire running to it. If the plunger doesn't move anytime, you could need a new one. I had to replace the one on my truck a few years ago, and know when I was adjusting the new one, I had it set originally so that it was holding the linkage a little too far open, and it sounded like the engine was on fast idle and when I tried to shut it off, it dieseled.
As I recall, it wasn't too expensive so you might give this a try. Sorry I don't remember the exact name, it's just been several years since I had to purchase one.
Jason
1993 F-150 300 I-6/5-Spd.
1977 F-250 351M/4-Spd.
Laughing Gas
Joined: Dec 2000
Posts: 781
Likes: 18
From: East Texas
'78 351M Choke adjust?
weldman,
There should be contact by the plunger on the linkage.
I'm not sure about the accelerator pump or which hole it should be in. I'll look at mine and try to post later. (I'm driving the 93 today.)
Jason
1993 F-150 300 I-6/5-Spd.
1977 F-250 351M/4-Spd.
There should be contact by the plunger on the linkage.
I'm not sure about the accelerator pump or which hole it should be in. I'll look at mine and try to post later. (I'm driving the 93 today.)
Jason
1993 F-150 300 I-6/5-Spd.
1977 F-250 351M/4-Spd.
Posting Guru
Joined: Aug 2000
Posts: 1,984
Likes: 2
'78 351M Choke adjust?
Weldman, the fast idle cam on your automatic choke could be holding your throttle open. These cams get worn and gummed up, and will not release completely. Squirt it good with some WD-40 or carb cleaner and see if that helps. Don
"Nothing lasts forever except natural stone and old Ford trucks." (Willie Nelson)
"Nothing lasts forever except natural stone and old Ford trucks." (Willie Nelson)
Thread Starter
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Fleet Mechanic
Joined: Feb 2001
Posts: 1,290
Likes: 15
From: Toronto, Canada
'78 351M Choke adjust?
[font size="1" color="#FF0000"]LAST EDITED ON 03-Jun-01 AT 10:46 PM (EST)[/font][p]Thanks for checking your linkage firstonraceday!
Still chasing the gremlins!!!!
Where is my fast idle cam located/what does it look like as mentioned above?
Thanks!
https://www.ford-trucks.com/dcforum/User_files/3ae0a7e34062b4ad.jpg https://www.ford-trucks.com/dcforum/User_files/3ae0a7b33fe32dbb.jpg
1978 F250 4x4 - 351M
Don't crush them, restore them!
Still chasing the gremlins!!!!
Where is my fast idle cam located/what does it look like as mentioned above?
Thanks!
https://www.ford-trucks.com/dcforum/User_files/3ae0a7e34062b4ad.jpg https://www.ford-trucks.com/dcforum/User_files/3ae0a7b33fe32dbb.jpg
1978 F250 4x4 - 351M
Don't crush them, restore them!