I've got a '78 F100 Explorer with a 302 V8 in it. I picked up a Hayes manual and have started trying to un-jerryrig my engine. I just redid all of the vacuum lines that were there, but that's not saying much. The tree off the intake only had a couple of routed lines, the others were all capped off. Now according to the diagram, my air cleaner has two nubs on the top- one runs to a thermostatic control thing in the nose and the other goes to "vacuum source" (that's all it says, no mention of where it's supposed to go). Mine, on the other hand, goes nowhere since there's no hose at all! Can anyone tell me where all the vacuum lines off the tree (4 total if memory serves) are supposed to go? There's a big one that runs to the master cylinder, that's ok, it's most of the little 3/16's lines that are all mangled.

Off to the side a bit from the tree is another two prong "tree" that also has 3/16's lines. Only one of those is going somewhere, the other runs to about 4" worth of hose with a screw in the end of it (much like the ones off the tree mentioned above). Any idea where these *should* go?

NmumberDummy, and anyone else, can you give me the part numbers I need to hook the 1/2" (my guess) hose from the back side of the air cleaner (closest to the dash) to the passenger side rocker cover? There's a hose from the cleaner to an elbow, to a grommet or somethingoranother in the rocker cover. Also, I need to know the part number for the shroud that goes around the passenger side exhaust manifold, the tube that connects the shroud to the nose of the air cleaner, and the part number of the flexible/accordion hose that runs from the cold air intake in the grill to the nose of the air cleaner.

Now, when I have all of this redone I can begin to reset the carb. Any friendly instructions (with pictures!) out here on Ford-Trucks? Lately my truck's MPG sucks and the exhaust smells like it's running rich (big stink). It also heasitates every once and a while at idle (not exactly a pattern, 3 seconds, 5 seconds, back to back, etc.)- my guess is it's fighting the rich setting when it pools up. The Hayes manual says to turn this and that, but I can't rightly say which carb is on there other than it's a Motorcraft (no tag). Any idiot-proof guide to id and adjust my carb?

Thanks all!!

 

The vacuum tree on the back of the manifold is for supplying manifold vacuum to anything that may need it. Power brakes, heater controls, auto trans vacuum modulator, and air cleaner warm-air duct system are common connections.

The air cleaner warm-air duct system you are asking about sources off manifold vacuum; the aforementioned vacuum tree is a good place, many carburetors (including the stock 2-barrel) have a manifold vacuum connection as well (this is vacuum below the throttle plates. Vacuum above the throttle plates is called "ported" vacuum). From the manifold vacuum source, it runs to a bimetallic vacuum switch on the air cleaner. It doesn't matter which side of the 2-port switch you connect the source to because it is an open\close switch. The other port of the switch is then connected to the "vacuum motor" on the snorkel of the air cleaner - the small can that opens\closes the door in the snorkel. Before you spend time plumbing this up, check that the vacuum motor on the snorkel actually holds vacuum in the first place. These almost never stand the test of time. If it is ruptured and you run it that way, you'll have a vacuum leak. In this case you'd be better leaving the system capped off and disabled. It keeps the carburetor from icing over on cold mornings when their is moisture in the air, but a lot of times people can get away without using it.

As for the smaller vacuum tree with the mystery line and the screw - the screw is most likely there as a plug. This tree is there if you need it, but if you don't need it, don't worry about finding things it should have gone to; instead just cap off unused ports.

As for the hose from the back of your air cleaner to the valve cover - this is a PCV breather hose. Typically, there is a grommet in the valve cover, with an elbow that connects to the hose. The hose goes up to the air cleaner, then connects with a fitting\elbow to a breather filter. Breather filters are easily available at most parts stores. Most PCV plumbing hardware is usually available at most parts stores in blister-pack packaging in the "HELP!" isle.

Sorry I cannot help you with the part numbers on those air cleaner hoses but most parts stores have bulk cut-to-length hoses for these applications.

As for dialing your carb in - if it's been a long time since the carburetor has had any attention and it's really filthy with varnish and debris, a carb rebuild is in your best interest. You most likely have a Motocraft 2150 carburetor. As for your rich problems, it could be anything - float height, ruptured power valve, stuck choke, idle mixture screws too far out. Let me know how you want to go about this. We can go step by step to isolate these issues, but personally, if this were my truck, I wouldn't bother resetting a float on a gummed up needle and seat; I'd just rebuild the carburetor. Let me know what kind of shape yours is in. I personally tend to go the longer route up front so that things are fresh and simpler in the long run. If I seem a little "trigger-happy" when it comes to advising people to rebuild carburetors, it's because I can do it myself for $50 in a kit and cleaning supplies, which is less than what most people throw at it in fuel pumps, filters and other tune-up parts when a properly set up carburetor really would have solved the problem in the first place.

Last but not least...instead of worrying where your existing hoses should have gone, start over from scratch and refer to my diagram below. Your truck sounds like one of those where a previous owner thinks he could figure out a better way to plumb an engine than Ford did, and then scratched his head when the motor wouldn't well. Don't you just love when people do that?

 

I know at least one of the vacuum lines ran into the carb. I'll try and get some decent pics tonight, mark them, and post them up. I'm kind of agreeing with you about the carb rebuild. I've never done one, but it makes sense to just start from scratch rather than troubleshoot a big old mess of "duct tape and bubblegum".

Thanks!

 

Hey guys, I just got "done" doing the same thing on my truck. The vacuum lines were kind of a mess but I believe they're back together correctly. fmc400 you wouldn't happen to have a vacuum diagram for a 1979 400cid 6.6L would you? Washington State?

I had a question about adjusting my air/fuel mixture but I'll save that for another time. I agree about rebuilding the carb. I'd like to start fresh too but, right now, I just need to make it get on the road.

 

Sorry, I do not have any specific diagrams in that sense, the one above is just a general one. It's a "best fit" one. Chances are your truck wouldn't be too different, but you may be able to find what you need from Autozone's website. If your truck wasn't originally a CA smog setup, it'd be simpler and closer to the diagram above.

As for the air\fuel mixture (I assume you're talking about the idle mixture screws) the best way to set it is with a vacuum gauge. That will get you the perfect setting. If you don't have one, a ballpark method is to turn both screws all the way in, then back them both out 1.5 - 2 turns. I set mine with a vacuum gauge, and personally it's the best diagnostic tool I've ever bought.

 

I guess when I say air/fuel mixture, I mean rich or lean mixture. It seems my carb is not getting enough air to vaporize the fuel.
I'll check out that vacuum gauge.
To go into it a little deeper... The reason I think my air/fuel mixture is wonky is because I just replaced my air cleaner housing. The one that was on it before was a pretty serious hack job. The body of it was okay but the lid was just plain bad. I should take a pic of it. The wingnut and washer would just go through the big hole at the top and not secure the lid. The back of the lid had a big piece cut out of it but someone had screwed on a small piece of metal to keep water from getting in. Basically there was plenty of air getting in because there wasn't a good seal between the lid and the body. Since I made everything as it was supposed to be, less air is getting in and the engine is hard to start. It gets to the point of just being on the edge of starting but won't catch. I give it a slight tap of fuel and it won't catch at all.
I finally got it started by removing the air cleaner lid completely. Once it warmed up it ran fine.
*whew*
Sorry to take up your time with this

 

So, let me get it straight - it runs fine without the air cleaner, but it won't start with the air cleaner?

 

It will start with the air cleaner when it's warm. I just went outside and started it. It was still somewhat warm. I'll try it again tomorrow when it's really cold to see what happens. I guess, yes. With the air cleaner housing closed it has trouble starting. I'm sure there's no obstructions in the pipe/barrel part of the housing.
it gets right to the very edge of starting but just can't seem to catch.

 

Let me know how it starts cold; it could be a choke issue and not related to the air cleaner.

 

Will do.
Choke issue like it's letting too much fuel through?

 

i have them just dont have a scanner, give me 12 or so hours from this post and ill post them. a good investment is a chiltons manual thats where i am getting the vacuum diags from

 

Hey jc,
If it's a matter of scanning the Chilton's book, I've got it. I appreciate the effort but don't worry about doing the scan. I was just hoping for a simplified version. Yeah, I'm lazy.
I've got the Hanes and the Chilton book, what one doesn't have the other does but there are some things they both don't have. I was thinking about picking up a book on the 400cid engine. I'm a noob when it comes to deep automotive things.

 

Hey fmc,
I tried to start it cold and the same thing happened. It turns over and sputters like it wants to catch and start but it doesn't. Then it'll just turn over till the batt starts to run down. I pulled the lid off the air cleaner housing and it acted like it wanted to start but just wouldn't catch. It would just sputter.
I'm recharging the battery now. I'm betting once the battery gets a full charge and the air cleaner lid is off for a bit it should start.

 

yes, it started.
Also, it has a little bit of an "after-run". Where you turn off the key and the engine sputters before it finally stops.

 

The starting problem sounds like a choke problem. In my opinion you're just chasing your tail with the air cleaner. As long as the air filter can breathe, the air cleaner housing can't really cause any problems. The next morning, push the gas once, then pull off the air cleaner and take a look at the choke plate to see if it snaps shut. The choke on a 2 barrel is actually kind of complicated. If you want to see it, here is my write-up on the complete, proper factory procedure for setting the choke up on a 21XX Motorcraft carb:

https://www.ford-trucks.com/forums/7...ml#post6422219

The after-run is called dieseling, it can be caused by many factors: high combustion chamber temperature (due to lean fuel mixture or late timing), high curb idle, carbon deposits, vacuum leaks, low fuel octane. Most of the time it is high curb idle.