Won't idle.. problem found

[Nightstick]

Hey y'all, so I took the new to me trail rig out today for a shakedown run to tie up any loose ends before OCBR. All the good stuff aside, I'm having an issue with the idle.

When I start it from cold, it will idle up and down and almost get to the point of stalling if I don't keep feathering the gas. Once I got it warmed up it idled fine for a while, then started having the same issue even at operating temp. I have a couple theories as to what it could be based on experience and some others having the same issue.

Timing: haven't checked it yet

Heat soak: I don't think this is the issue. I let it cool down completely, and it still has the same issue. Not only that, but if I let it die, it fires right back up no problem even after sitting a while.

Ignition system: it has an MSD HEI setup in it, so IMO it's unlikely this would be the problem.

Fuel system: brand new fuel cell, filter, and newly rebuilt carb. I suppose there could be an issue with the carb, but I would think any problem it might have would be present throughout the RPM range, not just idle. I have adjusted the idle screw to no avail.

Vacuum: since I just replaced the carb, that gasket is new. The PCV is routed to the distribution thingy at the back of the motor, and one line coming off of that goes to the passenger side of the carb. That is the only vacuum line hooked up. Vacuum advance is not hooked up either.

So, I'm thinking either timing or vacuum. Obviously I can check the timing, but the vacuum line stuff is a mystery to me. Any help on that subject, or other theories are appreciated.

 

[70_Steve]

... I have adjusted the idle screw to no avail.

Did the idle mixture screws make any change at all?

 

[Nightstick]

Haven't tried those yet, steve. 1/4 turn at a time, in is leaner out is richer, correct?

 

[70_Steve]

Haven't tried those yet, steve. 1/4 turn at a time, in is leaner out is richer, correct?

Correct.

 

[Nightstick]

Correct.

I'm assuming I have a lean issue?

Aside from dealing with the current problem, do you see any issue with the vacuum advance not being hooked up or how I said my vacuum lines are routed?

 

[bax]

What kind of carb? why is the vacuum to the dist not hooked up? Pcv go to big vac port on the back or side of the carb.

 

[Nightstick]

Motorcraft 2150. No idea why it isn't hooked up. Is it routed to the distribution block or a port on the carb? There's a line there that's capped, and looks like it went to the dizzy at some point, but it hasn't been hooked up since I've owned it

 

[hucklburry rev2]

A vacuum gauge is really cheap and worth gold when playing with a carb'ed engine. Get one (I plug in a hand vacuum pump for bleeding brakes, it has a gauge on it, works awesome). You can google "vacuum tuning a carb" and see it is a great tool to use.

Go check your timing and use the vacuum gauge to see she is doing, vacuum tune the carb and see how it goes.

 

[70_Steve]

The PCV is routed to the distribution thingy at the back of the motor, and one line coming off of that goes to the passenger side of the carb. That is the only vacuum line hooked up. Vacuum advance is not hooked up either.

Aside from dealing with the current problem, do you see any issue with the vacuum advance not being hooked up or how I said my vacuum lines are routed?

Vacuum tree/distribution thingy usually comes off one of the runners in the manifold. Not the best place to connect the PCV. You really want the gasses that come through the PCV to be evenly distributed across all the cylinders. That's why, as bax said, the PCV is usually connected to something right at the base of the carb.

That other line that you said comes off the tree and to the passenger's side of the carb doesn't sound right.

A couple pics of what you've got would help.

Found the pic below on-line.

 

[Nightstick]

My mistake, the PCV line does go from the valve cover to the carb riser... I'll get some pics tomorrow.

Thanks for the responses so far fellas!

 

[73azbronco]

Picture of what you are describing helps more

 

[Nightstick]

So here's what I have. There's a large vacuum line going from the valve cover to the base of the carb. There's a line going from a port on the intake manifold to a distribution thingy wity two lines coming off of it. One goes to the passenger side of the carb and the other is capped, which presumably went to the dizzy at some point. The PCV plug going into the valve cover does not have a good seal on it.

 

[Nightstick]

You can see that the choke is not hooked up also. I can see how this would create a problem when the motor is cold, but not at temp.

 

[BRONCROB]

You can get by without a choke but yours appears to be closed.Loosen the screws on the choke housing and rotate it until your choke opens and see if that helps.

 

[Nightstick]

You can get by without a choke but yours appears to be closed.Loosen the screws on the choke housing and rotate it until your choke opens and see if that helps.

Opened the choke, no change. I didn't get it up to operating temp though. It is also hard to keep it at any rpm under 1200-1500 or so. If I try to just give it a little gas it still wants to stall, so it's either Rev it high or nothing... To describe it differently, when it fires up it gets up to say 1200rpm then immediately goes down and stalls. Doesn't try to idle. That is slightly different than what it was doing yesterday when it would try to idle for a second before dying. I'm assuming it's because it's completely cold now.

 

[70_Steve]

Who rebuilt the carb?

Turn the idle mixture screws in until they just seat. Then back out 2 1/2 turns each. If you mess with them, try to turn each of them the same amount, until you get a vacuum gauge or low range tach to accurately set the idle mixture.

When will you check the timing?

 

[Nightstick]

Who rebuilt the carb?

Turn the idle mixture screws in until they just seat. Then back out 2 1/2 turns each. If you mess with them, try to turn each of them the same amount, until you get a vacuum gauge or low range tach to accurately set the idle mixture.

When will you check the timing?

Another member here who shall remain nameless, lol

I'll be able to mess with it wednesday morning, so I won't have much more info until then. I picked up a tach today though.

Edit: I just read over the idle mixture adjustment using the low range tach and vacuum gauge. I don't have either of those. Seems like that's more of a fine tuning thing, which would be great, but I can't even get it to idle at this point. Frustrating

 

[Nightstick]

I lied... I ran out there and set the idle mixture screws at 2.5 turns out from bottom, same thing. When i ran them in, I didn't count, but they felt like they were out about that much already. I'll try to run a vacuum gauge on it as soon as I can.

 

[bax]

run the screws all the way in and see if it dies. If it dont you have a vacuum leak somewhere,

 

[Nightstick]

run the screws all the way in and see if it dies. If it dont you have a vacuum leak somewhere,

The idle mixture screws?