Well I am stumped, please help me!

OK, so I am having this problem. My engine is a freshly rebuilt Ford FE 360. Stock intake manifold, stock cams, stock everything. It's in an 1976 F-150 truck. The carburetor I put on there is practically brand new but I think it might be the wrong one because the engine won't run well. Someone purchased this carb and threw away the one that originally came on the engine. It is a Motocraft 2150 carb. It says AN2 1.21 on the side. My homework says that means the venturi size is 1.21 and it is a 351 CFM carb.

My vehicle has an EGR valve which mounts on a spacer underneath the carb and is turned on by spark vacuum only when the engine is heated up. A ported vacuum switch keeps EGR from engaging until the engine is warm.

My vehicle also has a PCV valve system. The PCV valve is on the passenger side valve cover and then there is a breather on the driver side which has a hose to bring in fresh air from the air filter body. There is a breather filter there.

The vehicle does NOT have a smog pump. It also doesn't have a charcoal canister or whatever that is. Only PCV and EGR.

The carburetor has a fat connection on the back (where I have PCV connected), then it has a small connection on the back (don't know what it is, probably manifold vacuum), then it has the "spark" connection on the side underneath the choke (I have EGR and timing advance hooked here). Then it has the "air horn" connection, on the top, and then on the front underside, on the driver side, there is a connection that is not used. I read somewhere that this connection was for some kind of charcoal canister system.

What is happening is, when I try to set the timing to around 10 degrees BTDC, the engine practically won't run. It just kind of wants to stumble and die. I have to set it at 15 degrees BTDC for it to stay running at idle. It also won't start unless I have it around 15 degrees BTDC. Even then it is hard to start and I have to feather the gas pedal.

When the engine is at normal operating temp, I try to set the idle mixture screws, using a vacuum gauge. I can not get more than 15 on the vacuum gauge, no matter how far I turn out the screws, and if I turn them in too far the engine starts to die.

So, if I set timing around 15 degrees BTDC, then when I try to start going from a stop, the sudden accelleration makes the engine backfire out the carb and die. Also if I am going along with the engine at high revs, then let go of the accellerator, the engine wants to stumble and die.

I checked the vacuum system very carefully and I can't find any vacuum leaks. Everything seems fine with the vacuum connections.

So, my little brain is thinking, maybe the engine is running way too lean all the time? I checked the fuel filter and it's fine. The fuel pump was also replaced recently.

So what I'm thinking is, what if the person who bought the new carb didn't know exactly which one to buy, and got the wrong one? Maybe they got a carb that had the wrong jets for this setup? If the jets are too small wouldn't this cause a lean condition all the time, forcing me to run timing that is advanced too far?

On a motocraft 2150 can I find out what jets are in there? Can anyone tell me what jets this particular engine and vacuum setup call for?

Or do you have other ideas? I have a vacuum gauge, a tachometer, and a timing light. I have followed the directions for setting timing, idle mixture, and idle speed. I just can't seem to make this engine run right, it acts like it is always going to die.

The thing that makes me suspect the carb is, this carb was purchased before the engine was replaced with a new longblock. The old carb was damaged so they just bought a new carb from Autozone. They weren't sure which carb to get so maybe they got the wrong one? Anyway, the OLD engine was running like this too. They had a mechanic adjust the timing and it ended up advanced way far like close to 20 degreees BTDC. The mechanic also plugged off the vacuum timing advance even though the advance works. I think he did that because the timing was already so advanced it couldn't go farther. The engine was overheating and it had bad valves and rings so I swapped in a rebuilt longblock, and the carb was so new I just rebuilt it and swapped it over... and now the new engine is acting the way the old one was acting. BING this makes me think carb problem!


Anways please share your wisdom...

 

Did you replace the harmonic balancer? I wonder if the outer ring has slipped and it is actually reading the timing marks wrong. At 20btdc, does the engine turn over easy when hot? not dragging the starter?
Just for giggles, advacne the timing as far as you can until it drags the starter when hot, then slowly back it off until it doesn't. See what your timing light says. See how it drives that way. If it runs good and doesn't drag the starter or ping, then it should be good there. If it is reading really high, the balancer may have slipped.

 

darn it... my balancer totally must have moved. I advanced the timing to what would probably be 40 or 50 on the balancer and it runs great!

My Duraspark module was bad, my dizzy cap and rotor were bad, and the balancer was slipped. Argh... But it runs good and smooth now!

One thing that is still an issue, is AFTER I accellerate, when I then let go of the gas, the engine wants to die.

I think this might be an idle mixture issue, but I am having trouble adjusting the idle mixture, I can't seem to get the idle vacuum higher than about 15 at 500 rpm or so. It seems to stay around 15 no matter where I turn the idle mixture screws, but then if I turn them in too far or out too far the engine just dies.

What RPM am I supposed to be idling at when I set the idle mixture?

 

About 650 to 700 in Neutral is the norm. That might be why it wants to die too.