Hey all.

The following question isn't about a truck per se, but you guys know a lot more about these Cleveland engines than my car forum does, so I thought I'd come here and ask for some more specific advice. To introduce, I have a '79 Lincoln Continental with a bone-stock 400 in it. It's been sitting, covered but neglected, for 16 years, until I pulled it out earlier this year and gave it some attention. I rebuilt the carb and put in all new ignition parts and it starts and runs... mostly. When the engine is hot, everything is gravy and it starts, idles, and drives like a champ. When it's cold, I pump the gas to set the choke, turn the key and it starts right up. It revs up to a high idle and immediately dies. If I put my foot on the gas, it'll catch, and it'll stay running (very roughly) until it warms up. My foot doesn't need to be on the floor, partial throttle will keep it running. The rough idle won't clear up on its own when it warms up - if I still have my foot in the gas, it'll stay running rough until I let off; the engine will slow down until it sounds like it's going to die, then it'll magically jump up to its warm idle RPM and smooth out. I have read fmc400's excellent post on adjusting the Motorcraft 2150 choke (several times, in fact) and have replaced the choke pull-off and thermostat, as well. Does anyone have any suggestions what to look at? Thanks in advance.

 

First, welcome to FTE!

Second, it sounds like you have too much choke and maybe too little choke pull-off. Try backing the choke off a notch or two and see if it changes the symptoms.

You can run too much choke if you have sufficient pull-off. And there almost isn't such a thing as too much pull-off as the engine will slow, decreasing vacuum and therefore pull-off, if you have too much. But, you can get into an oscillation mode with too much.

 

Thank you. I have been fiddling with these adjustments for a couple of weeks and apparently, my engine just isn't happy with the factory settings. I'll keep playing with it and see if I can get it dialed in.

 

Just remember what the settings were before you change so you can get back. And, make sure you dial in the idle mix when the engine is warm. Also, where do you have the vacuum advance connected? Manifold vacuum will exacerbate any engine RPM changes, making it very hard to dial in. I highly recommend ported vacuum.

 

It's on ported vacuum. Actually, the vacuum advance seems to be kind of screwy; I was going to adjust the timing about a month back, which you have to disconnect the vacuum advance for. When I unplugged the vacuum advance, the idle jumped up from its 800-ish RPM to around 2400 RPM. Plugging the vacuum lines did not drop it back down. Obviously, I wasn't able to verify or adjust the timing, but I never could figure out why it would do that.

As far as the choke is concerned, I did get to watch it once while my wife started the engine. It stalls out as the pull-off is opening the choke blades. Is it just not opening them far enough fast enough, then?

 

I would verify that it still does the RPM jump if you pull the vacuum line, as that is indicative of a significant problem - like not enough pull-off and too much choke. And, if it does do it then try to ascertain what is happening.

Here's my guess: If there's too much choke and not enough pull-off the vacuum will be low due to too much fuel. Pulling the vacuum line introduces air into the mix and leans the fuel, so the RPM goes up, as does the vacuum. The additional vacuum starts bringing the pull-off into action, which opens the choke, which raises RPM, which raises vacuum, which pulls off the choke, which raises vacuum, which.......... In the end the engine is running well but the throttle is on the fast-idle cam and the RPM will be quite high. Probably by blipping the throttle the idle will come down.

 

Actually, I pulled the vacuum advance line when it was warm, so the choke wasn't in operation. I'll definitely try dialing the choke back; I've had it between 3 Rich (the factory setting) and the index, and nothing's changed. I haven't tried giving it more pull-off, though I've definitely given it less and that hasn't changed anything, for obvious reasons.

 

You can overpower the pull-off with your fingers - either by pulling the choke plate open or pushing on the piston. If that helps the engine then you know which way to go. But try to dial the choke itself in first. Many carbs don't have the pull-off and get by fine with just the choke, so the pull-off is fine tuning. Get the choke right and then dial in the pull-off.

 

I'm wondering at this point if it's maybe a vacuum-related issue. Leaning up the choke and backing off the pull-off did nothing. There is another issue with the engine; I wasn't sure if it was related originally, but now I'm wondering. When warm, it idles smoothly and runs smoothly under load, but when cruising at part throttle, it sputters and backfires. Later on tonight, after it cools down, I'll be taking a look at the vacuum advance to see if it's actually working. I'm wondering if, since the vacuum advance is hooked to a ported vacuum switch, that might also have something to do with the poor cold idle and that it seems to switch over to smooth running only after I completely release the pedal.

 

The easy way to see if the vacuum advance is working is to pull the cap on the dizzy and watch the innards while you pull a vacuum with your mouth on the hose. If it is working you'll see the stator rotate.

But, you didn't say the advance was hooked to a switch. I assumed it was directly to the carb. You might try hooking it up that way.

 

Switching topics to the third of three potential culprits, EGR. I just went out and looked at it, and the EGR valve felt like it was jammed open (I couldn't move the diaphragm by hand, it felt tight against the top of the valve). I will be tearing into the EGR system this week to clean it and see if that could be causing some issues. I have a question about that, though: My EGR setup has a Load Control Valve that switches the vacuum to the EGR valve itself. My vacuum diagram shows this is supposed to pull off of a port on the carburetor that my carb, unfortunately, does not have. Is there another place I can tee this off of to get the correct signal?

 

If your EGR valve is stuck open you'll fix several symptoms when you repair it. But, I don't know how to control it, so I hope someone will come along to answer that question.

 

Thanks for your help. It's much appreciated. It's been a real learning project.

 

It's been a while since I've checked in here, sorry. I tried replacing the EGR, but no dice. At this point, I'm not sure what to do, but the two suspects I have left are carburetor jets and the vacuum advance/distributor baseplate. I took a video of the engine starting when cold: https://youtu.be/u7v3PzoZ0m0

Any more suggestions?

 

The problem turned out to be the advance after all. I currently have it disabled while I work on figuring out if it's the advance unit itself or the advance plate in the distributor. Either way, it may be simpler to just drop a new distributor in it. Thanks for the advice and help, and happy motoring.