I am really stumped and I'm about to set the friggin' truck on fire.

This stupid Motorcraft 2150 carburetor has given me nothing but problems after rebuilding it.

The issue is, it won't idle at all. I have to step down on the gas a little to stay running otherwise it will die. If I put it in Drive, it will die also.

EGR, manifold to carb spacer, spacer to carb gaskets are all new Fel-Pro gaskets when the carburetor was rebuilt.

I've tried everything - double checked my rebuild process, all was OK. Checked the settings (fast idle & choke) all was OK. Yes, I even tried fmc400's famous link. All leads to no solution.

I checked the base, and I retorqued the carburetor. I ended cracking one of the mounts. UGH! Not completely, but a crack is visible. I also saw the throttle shaft was a little wet. I sniffed it, and it smelt like gas. What's up with this?

I'm thinking of just throwing this carburetor away and either rebuild another 2150 (if any of them are compatible, I have no clue) I have quite a few of them. Or buy an aftermarket carburetor.

Is there any remote chance I may have missed something? This is not my first time rebuilding a 2150. I've never had problems before this one.

 

Did you get your idle mixture adjusted correctly?

 

Well shucks. The wetness on the throttle shaft is due to throttle shaft bore wear. The metal around the throttle shaft where it goes into the throttle body has worn away due to years of friction as the plates open and close. Over time gas seeps through the compromised seal. It's extremely common. Unfortunately there is no factory provision for bearings here, but some machine shops will bore and bush the throttle body. However, depending on how much it's actually leaking, it's not always a problem. While I'm sure there are some small issues with vacuum here, it's certainly not enough of an issue to make the truck fall on its face.

How does the vacuum look? Have you had the chance to hook up a gauge, or sprayed for leaks? Sometimes the movement of the needle can point you in the right direction. Depending on how all that goes, it might be worth your while to pull the EGR spacer plate and check the mounting surfaces with a flatbar and a feeler gauge. Those things burn out pretty easily (even the cast iron ones). I can see how something like that would show up after the plate has been pulled, because the edges of those get clogged up with carbon and rust. Maybe that was sealing things up for you, and now that everything's clean, it's not flat enough to seal.

I certainly trust your work with the carburetor internals. Have you had the chance to run the motor with the air horn removed from the carburetor? That's one of the great things about 2150s; being able to check the float height when wet. Where does it sound like your idle speed is set?

 

First time after the rebuild, it was out 2 turns. When that didn't work, I tried 1.5 turns. No go. Then tried 2.5 turns. No go.

I'm thinking if I have an extremely large vacuum leak, I may turn out 4 turns to see what happens.

 

2150 is a real simple carb. I doubt whether you did anything wrong in the rebuild....You are probably right, large vacuum leak......start spraying starting fluid around all the vac. hoses and vac. op. stuff and watch for rpm increase.

 

Throttle shaft wear? Well, I'll be. I hear that means death for a 2150. If it leaks, it means it has a vacuum leak as well? How bad is bad? If it requires going to a machine shop, I think I will just replace the carburetor. The truck has over 200k miles on it, but paperwise, it is exempt. How many miles left, I'm not sure. When I bought it, it sounds good. I did have a little hesitation when I drove it home. Neither the carburetor or the engine is original.

I have not tested for leaks. I can't do much diagnosing without my foot on the gas in order to keep it running. Vacuum system has been modified at one point. Some emissions devices are missing. The engine is not original. Valve cover says 1977 car. Think I'll just rip out everything and plug up holes until I can resolve this. Is it OK to temporarily run the EGR without its vacuum? The spacer looks OK. I dipped it in carb cleaner and scraped the remains off in the rebuild process. I see no piting. I'll check its flatness.

No, I did not check the float while it was running. As stated earlier, it won't idle. I guess I can jam something on the throttle to keep it running without touching the gas pedal. Should I start naming my beneficiaries? The idle sounds OK before the rebuild. About 700, I guess, and after rebuild...who knows, it varies depending on how far I press down the gas. When I take the gas off, it dies down smoothly.

 

There is a slight vacuum leak created by the throttle shaft wear, since it's right at the throttle plates. It's hard to quantify the point at which the wear becomes a problem; I don't have a great answer for that. If a significant amount of fuel is leaking from this area then it's a problem. If it's just slighly gummy, it's probably not an issue. You can try disconnecting the throttle linkage and see if you can actually wiggle the throttle shaft around. I've seen it that bad; if that's the case then it should definitely be junked.

Running without the EGR while you're just trying to get it going won't be a big deal. You're just trying to get it to idle for now, and the EGR valve wouldn't be open at idle anyway. Once you've got it back on the road and are driving it a lot, you'd want to hook it back up. I wouldn't jam anything in the throttle to keep the idle up, I'd just increase the idle using the curb idle screw until it's high enough that you can run it so you can diagnose it. You'd want to have it out of gear of course, and set the parking brake and maybe even chock the wheels. I've had my truck run off on me before. I had it in park with the hood up, and it put itself in reverse. I thought I was going to have a heart attack; I was able to dive in the cab and get on the brakes before it ran into the neighbor's car.

 

Thanks.

Hopefully turning up the idle speed will make it stay running. The parking brake is good, and the shifter is still opreational. I usually like to wrap the shifter in a bungee cord anyway and block the wheels.

Turns out the emissions section of vacuum routing was modified. I discovered nothing was hooked up except the distributor that goes to the port below the choke. Everything else was left dangling. The rest were untouched originals. I have A/C, auto trans, and cruise....so quite a vacuum web at the back. I'll replace those, it's due.

I investigated the old and original gaskets. They made good contact. I clearly can see the impressions on the gaskets from the spacer and the carb.

I decided I'll see what kind of vacuum readings I'd get anyway. I do have decent vacuum, but it's not properly diagnosed. I got as much as 26 Hg after instant deceleration. When dying, it reads near zero. At most, it's running around 15-20. Needle shake is visible. I may have either a wild cam or a valve needs to be looked at.

EDIT: Anyone know where I can get a replacement C-clip for the automatic transmission kickdown linkage? Mine flew off.

 

Welp, I finally got it idling on its own. I had to turn the curb idle speed screw in 7 or 8 full turns before it could idle on its own. I think some idiot turned it back out from an issue or something. Not high, sounds like about 500-600. Starts a little easier now, too. Still have that rough idle. It was starting to rain, so I had to hold the tuning for now. But at least it runs on its own now and in reverse and drive to boot.

Hope this carburetor still can service me for a good while after tuning. I do get a slight black smoke if I step on it.

Still need a C-Clip...kickdown linkage keeps slipping off.

 

I just got a new clip from the hardware store for like .15 cents for mine.

 

Still here.

It can idle, but it's hard to get it in gear without it cutting out. After nearly at opreating temperature, I finally got the chance to drive it without cutting out. I'm pretty sure the engine was worked over. The truck shot up to 40 when I stepped on it. It went good otherwise, engine is healthy after giving it a full tune up including the idle mixture. It's currently set at 20 Hg. I have needle shake, so it's hard to follow. Should I leave it or try to go for 21 Hg?

I also am having trouble with the cold starts. It likes to die while warming up. New choke pulloff diaphragm, set it with a 9/16 drill bit and verified the screw was resting on the V notch. What else can I do? I turned in the fast idle screw a full turn to no avail. Any more, I think the cam will bind. Lastly, it's having a hard time shutting down quietly. After turning the key off, the engine jerks violently for a second or two while the ignition is being shut down.

 

Usually anywhere between 19 and 21 inches is decent vacuum; steadiness is more important than peak on a stock motor (some performance cams will cause the needle to bounce because of the longer duration). I can almost gaurantee that the bouncing needle and idle issues are symptoms of the same underlying problem.

How fast would you say the fast idle is set? I usually set it so that it's idling high, but not high enough that the motor is screaming or knocks really bad on startup (dry bearings plus high idle is bad news). Expect some decent RPM to keep it running. There should be a specification for fast idle speed on the valve cover sticker if it's still there.

The dieseling (run-on) can be a result of high curb idle, a vacuum leak, or something that increases combustion chamber temperature such as a lean mixture or improper ignition timing.

 

20 Hg is good enough, then. I wasn't sure due to the needle shake. It shakes within 20 Hg. Not over an inch, but within. I have no way to verify, but it doesn't sound like a stock motor at idle. It's pretty rumble-y. The oil pressure is pretty high for a 351M/400. Exhaust is stock. Guess I got a nice motor in this deal.

I dropped my tach, so I can't verify until I find a good replacement. The old one was a cheapie. If I had to guess, it's about 800-900. Almost the same as curb idle. Curb idle is supposed to be set at 650 RPM. That may have contributed to the intermittent run-on. It got bad once enough to soak the butterfly with a light coat of gas. It idles lower when cold. When warmed up, it's higher. Fast idle is supposed to be set at 1500 RPM according to my calibration specs. I tried screwing it in, but it is nearly all the way in now.

I tried to time it also, but it's damn hard to read the timing marks. Any way to make the marks bright as flashing neon signs for this four-eyed geezer? I need to set it to 14 degrees BTDC as per the factory calibration.

 

I usually scribe the timing mark of interest with white-out or a piece of chalk.

 

Must be frustration with a 2150 on a 78' F-150 with a 351m week. Having alot of the same troubles with mine. After rebuilding mine on Sun.,I stuck it on Mon. ran rough, but it hasn't ran in a while so kinda expected that. Noticed I forgot to hook up a couple vacum lines seemed to run good, Tues started it up and ran great, tonight I finally get the nerve to take it to the gas station, get 2 miles from the house and she dies, won't idle or run for more than 10 seconds, had to tow it home with my other truck pull the carb off again and go through it again. I hope I got the choke linkage right, it's been apart for a while as I was looking for parts. Sorry I had to vent a little.
Charlie