All,

78 F150 4X4 351M w/AT...OK, definitely had a bad choke pull off or pull down (they seem to call it both things). Put a new one on, and it's definitely working now. Pulls in when engine is running and holds vac. Did the adjustment on the pull down linkage. Everything's clean and not gummed up. But in typical ford fashion, I find a part that's definitely bad, replace it and still have the problem. Engine is still rough at idle when it's first started and it's warm outside (say, 80°-90° this is when the engine itself is cold and hasn't been running), in other words when there's no choke. After it warms up it's OK. Idles better when it's cold enough to activate the choke and fast idle mechanism. Carb is a newly remanned unit. Other than the bad idle when first started in warm temps it's doing OK now. Any ideas?

Stan

 

All righty, first for some quick clarification. The heat of a warm day is still cold compared to the temperature a warmed up engine operates at. So, if your truck has been sitting all night and the engine hasn't been run in a while, regardless of the outside temperature the next day your choke needs to be shut.

Here's why I'm saying this:

"Engine is still rough at idle when it's first started and it's warm outside (say, 80°-90° this is when the engine itself is cold and hasn't been running), in other words when there's no choke."

From this statement I am gathering that you are starting your engine cold with the choke completely open (no choke). If the choke is not open when the motor is cold (cold as in engine cold, a.k.a. been sitting all night), the lean mixture will cause a rough idle, and for two, if the choke is open, the fast idle linkage will not be in play and the idle will be too low for the cold motor.

My point is that the ambient temperature of a warm day does not heat the engine up enough to run the first few minutes without a choke.

I recommend that you set the choke in the morning as I described in that other post, landing on the setting as specified by the engine decal. Now, if after setting it there, you find that the motor is running like crud once the engine has warmed up (operating temperature), you can lean the choke out a bit...but not so far that the choke is open when the motor is cold (cooled down).

 

OK, I think I see what you're saying. I did set it the way you outlined in the other post in the morning. Maybe it was *too* cold then because in the afternoon (not run all day) the choke is not closed at start up, it's just sort of loose; not open, not closed. Now that the pull-off works, when it starts it pulls the choke wide open. So what I will try is setting it in the afternoon so that it's closed at startup and will allow the fast idle to be engaged. As long as it will still disengage when warm that should work.

Stan

 

Hmm....

Just to make sure; before you start your truck when the engine is cooled down, do you push the pedal? That pulls the throttle lever back, releases the fast idle linkage and lets the tension in the choke cap snap the choke plate shut. Say you get home at night and the engine is all warmed up. By morning the engine will definitely have cooled off, but the choke will still be held open until you push the pedal and "load the choke."

Had a question--you set the choke in the morning, didn't drive it then checked it in the afternoon and the choke plate was just kind of loose? That is not supposed to happen. If the choke is shut tight in the morning, it should be shut tight in the afternoon as well (if you didn't drive the truck in between). The ambient temperature is not hot enough to open the choke on its own. If this is happening, I would pull your choke cap off and make sure that the tab on the end of the spring is slipping into the slot on the choke lever inside the little housing.

Here's the story on the choke pull-down...and this may be your problem right here. The choke pull-down is not supposed to pull the choke open all the way; it only opens the choke slightly. The choke plate has to be open slightly so the carb can get air during warm-up, while still retaining tension in the choke spring. The way to set the pull-down clearance is to actuate the pull-down diaphragm, then measure the distance between the front of the choke tower, and the downward edge of the choke plate with a drill bit. The width can be found on a carb rebuild sheet or Chilton's; most people start with 1/8 inch and go from there. Also, if you change the pull down clearance you may have to recheck the fast idle cam index as well.

Sorry for the length, but I hope it proves helpful.

 

> Just to make sure; before you start your truck when the engine is
> cooled down, do you push the pedal? That pulls the throttle lever
> back, releases the fast idle linkage and lets the tension in the choke
> cap snap the choke plate shut.

Well, if I push the pedal at start up it works as you describe but ONLY in the mornings when it's cold enough that the choke housing spring is under tension. By afternoon the spring tension is gone and the choke plate is sort of loose. By that I mean it's not open, not closed. There's no tension on it either way (rich or lean). When it's loose in the afternoon like that the fast idle won't engage with a pedal push as the choke spring isn't tensioned. I think this is just due to the way I set the choke spring tension to begin with. I've simply got it adjusted too loose.

> Say you get home at night and the
> engine is all warmed up. By morning the engine will definitely have
> cooled off, but the choke will still be held open until you push the
> pedal and "load the choke."

Right, it works that way in the morning as far as loading the choke goes. By afternoon when the ambient temp goes up the choke housing spring becomes loose and you can't load the choke at that point (too loose for now, I'll be re-setting it later today).

> Had a question--you set the choke in the morning, didn't drive it then
> checked it in the afternoon and the choke plate was just kind of
> loose?

If I "load the choke" in the morning, then don't drive it, it will still be that way in the afternoon. However, with the choke NOT "loaded," the basic tension setting (the spring tension you get by rotating the choke housing) will be holding the choke in the closed (rich) position in the morning but by afternoon the spring tension will be too loose to hold the choke plate towards the closed position. Sounds like I need to set more choke tension in the afternoon so the choke plate is tensioned closed then too.

> That is not supposed to happen. If the choke is shut tight in the
> morning, it should be shut tight in the afternoon as well (if you didn't
> drive the truck in between).

If the choke is "loaded" it works that way. If it's "unloaded" then it's got spring tension in the morning but not the afternoon. I originally set the choke housing spring tension in the morning when it was about 60° outside but I set it to be *just* closed at that point. When it warms up by afternoon the choke spring tension is loose.

> The ambient temperature is not hot
> enough to open the choke on its own. If this is happening, I would pull
> your choke cap off and make sure that the tab on the end of the
> spring is slipping into the slot on the choke lever inside the little
> housing.

I think we had 2 different things going on here that I was confusing. There's the loading of the choke, and then there's the basic underlying choke housing bimetalic spring tension setting. Interrelated but not the same. I'll check the tab and re-set the choke spring this afternoon and make sure it's tensioned in the closed position. Also note that as far as I can see there are no marks on my choke housing to reference to the index marks on the metal ridge above the housing when setting the spring tension. Makes it hard to adjust to a specific setting!

> Here's the story on the choke pull-down...and this may be your
> problem right here. The choke pull-down is not supposed to pull the
> choke open all the way; it only opens the choke slightly.

The pull-down works correctly when the choke is tensioned closed (cold morning start). When the choke spring is loose in the warm afternoon as it is now the pull-down pulls the butterfly open as there's no spring tension working against it right now. Again I think this is because I have the choke spring tension set too loose to begin with, not that the pull-down is set wrong but I'll double check the pull-down.

> Also, if you change the pull down clearance
> you may have to recheck the fast idle cam index as well.

I'll check that again too.

> Sorry for the length, but I hope it proves helpful.

No problem, I appreciate the help. I've been fighting several problems at once with this "new" (remanned) carb from Parts America (a.k.a. Checker Auto). First off nothing was set or adjusted from the factory. Second, the choke pull-down on that carb was bad from the beginning (wouldn't pull in or hold in with vac applied).

I'll look at it this afternoon and let you know what happens.

Stan

 

I tried resetting things yesterday. I checked the spring inside the housing and I rechecked the fast idle and all the other crap on this carb. So I set the choke housing spring tension to close the choke plate with the engine cold in the afternoon. Seemed to work better at the time but of course it didn't work right today.

I just don't see how this thing will EVER work. While I finally got a good idle after adjusting it yesterday afternoon, and this morning it started OK, the $%^$#@ thing never released the choke after the engine was hot this morning so I spent a fortune in fuel to find out this thing still doesn't work.

Here's the dilema. If I dial in enough choke housing spring tension to close the choke in the afternoon when it's warm out and the engine is cold, I'll get a good idle at startup morning or afternoon (since I can load the choke and get the fast idle engaged both times with it set like that), but then the choke doesn't release once the engine is hot. On the other hand if I only dial in enough tension to close the choke in the morning when it's cold outside (say 60° or so), then I can't "load" the choke later in the day since there's not enough spring tension to close the choke plate and allow the fast idle to engage. So when it's like that it will still start OK with no choke but it idles rough and barely runs in gear (auto trans) at start up until the engine warms up.

It will start OK, starting is not the issue. It's the idle after it starts when the engine is cold late in the day when it's hot outside that's a problem. For now I've set it back to no choke spring tension with the engine hot so I don't dump another ton of fuel on the way home today.

THIS JUST DOESN'T WORK!! I'm missing something. I can't believe they designed this POS to operate this badly. There's got to be a piece missing from this puzzle. I may try swapping out the old choke unit from the old carb to the new one. If that doesn't help I may return the whole carb and try to get another one and see if that helps anything but due to (IMHO) a very questionable carb design I wonder whether or not that will help much. I might just get a Holley that has a manual choke and throttle hookup instead and dump this automatic choke stuff.

I'm only a wee bit frustrated this morning. Just a wee bit.



Stan

 

Back the idle screws out about 1/2 turn each and set the choke to work in the morning and see how it does in the afternoon.

 

Yep, that's what I'm beginning to think I need to do too. This morning I took the choke thermostat unit off the new carb and replaced it with the one off the old original carb. The old one is actually a much better quality unit and it's the electrically-assisted version I like better anyway. I checked the old one yesterday and found that it was working OK so I set it to just be centered for now as far as the little tick marks go. Choke loaded correctly this morning and was full open by the time I got to work. I'll see what it does this afternoon after it sits and the engine gets completely cold again. If at that time the choke can't be loaded, I'll try backing out the idle screws.

Stan

 

Well, after all the hassle with this new carb it looks like it was the choke thermostat. I put the old carb's choke thermostat on this morning and I set it to the middle index mark which closed the choke plate. Got to work and checked it and it was open. Start, fast idle, back to regular idle all OK this morning. Checked it at lunch and the choke plate was closed again (which is what I was hoping for). This afternoon I was able to load the choke, started OK, went to fast idle and then idled OK. When it warmed up it went to normal idle. Checked the choke plate when I got home awhile ago and it was full open.

This is all finally working like I figured it had to. If the engine is cold (regardless of ambient temps) the choke closes. When the engine is hot (regardless of ambient temps), it opens. Makes sense. An automatic choke like that really has to operate based on engine temp, not ambient. Next step is to call the place I got that carb from and see if I can't at least get the cost of that choke pull-down reimbursed.

So, the drill on this is:
• Unless engine has been running and is *hot*, mash accelerator pedal once to "load" the choke. Loading the choke closes the choke plate (butterfly) all the way and sets the fast idle cam into place.
• Carb is now at full choke to start.
• Start engine which goes immediately to fast idle. Should start easily and idle well if things are working right.
• Once engine is running the engine vacuum activates the choke pull-down/pull-off (which is *finally* working now that I've replaced it) which opens the choke plate just a skosh as per spec.
• Run it up to temp and the choke should open and idle should go down to normal setting.

I can see now why they augmented those carbs with an electrically assisted choke...it takes quite awhile for it to open with only hot air passing over it.

Stan

 

Glad to hear it's going good.

 

Good going. A free fix None better.