Motorcraft 2100 - Choke clean air tube with long tube headers

[GloNDark]

I've been searching this for months it seems, my 73 has the stock 2100 carb on it and most of the stock emissions crap as well. It has long tube headers on it, which have been on there for many years. The hot air tube runs down to a box that is hose clamped to the header tube. The choke seems to work well when cold and opens fully when warm.

Now the the "choke clean air tube" is air intake for the choke housing. It's used to draw in warm air from an exhaust crossover. The tube connects from the air horn to a plate on the intake manifold. One tube is the "clean air" which is basically just manifold vacuum. The other tube is for hot air coming from an exhaust crossover.

Now I don't have the stock exhaust crossover, and this clean air tube was plugged with a cap when I rebuilt the carb. My issue now is that it runs like crap when the tube is plugged but runs fine when open. ?:?

I'm at a loss as to what to connect this port to. Anyone have an idea what to do with this?

 

[oleguy74]

just cap it if you don't use it.

 

[GloNDark]

just cap it if you don't use it.

The issue is, it was capped for the longest time. I tore down the carb, cleaned rebuild it all and now it runs like crap with it capped. I've read lots about that line being hooked up but nothing about what is the right thing to do with headers installed.

I'm going to cap it tonight and see if I can tune the choke to work with it capped but so far i'm at a loss.

 

[73azbronco]

see below.....

 

[GloNDark]

I've got the thin metal line hooked up and going to the Choke heated air inlet already.

This port is for the vacuum port coming off the back of the air horn on the carb itself.

 

[73azbronco]

Now I see, that line also goes to the exhaust manifold, but I can't remember where, someone wil be along shortly, please standby...

OK, look here:

http://www.cjponyparts.com/CHOKE-TU...m-side-of-Choke-Housing-1969-1970/p/MUK1009O/


I think how the air meters is from that cold air fitting you pointed out down to manifold, it heats up then goes back up to carb choke plate.

 

[oleguy74]

choke should be electric also.some were some not.if electric will be ok,if not you can make a fitting welded to a header pipe.there may even be a kit available.if not used,will pull some dirt into carb.

 

[Justafordguy]

You need a metal line going from the threaded "choke heated air inlet" down to the header and wrapped around the header tube so it will heat up then back up to the "choke clean air tube" in your diagram picture.

 

[Ranchtruck]

The point of the choke clean air port is so the heated air being sucked into the choke housing from the heater box on the exhaust header is filtered. Right now it's sucking dust and dirt thrown up by the wheels into the area around the headers.

The flow goes through the air filter, then from the clean air port down to the header heater box, then up to the choke coil and it gets sucked into the intake through the vacuum port from there.

 

[Justafordguy]

The point of the choke clean air port is so the heated air being sucked into the choke housing from the heater box on the exhaust header is filtered. Right now it's sucking dust and dirt thrown up by the wheels into the area around the headers.

The flow goes through the air filter, then from the clean air port down to the header heater box, then up to the choke coil and it gets sucked into the intake through the vacuum port from there.

X2, exactly.

 

[GloNDark]

So it sounds like the only real "correct" way to run the Clean air and Hot Air tubes would be to weld bungs to the headers. Hmmm

 

[Ranchtruck]

Or switch to an electric or manual choke.

 

[Rustytruck]

You dont use bungs on the headers. The tube going down to the exhaust manifold is just a heat exchanger. It has nothing to do with exhaust gas. Your Choke clean air tube is just the fresh air in. Use a piece of rubber hose and connect to the steel tube running down to your header. Wrap a couple of wraps of steel tube on the out side of the most convient header tube and run that same tube up to the choke cover. The up to the choke side of the piece should have some fiberglass sleeve on it to keep it hot. There is a vacuum leak inside the choke cover that sucks the air through the tube you added. This way filtered air comes from the top of the air horn of the carborator down the little tube. The wraps around the hot header heats up the air and is sucked up into the choke cover. When the choke gets this heated air it sences the heat and allows the choke pulloff to turn off the choke and close the vacuum suction inside the choke cover.
The stock manifold has a piece in it making the heated air chamber. It is not open to exhaust gas.
I hope that helps

 

[GloNDark]

OHHHHHHHHHHH

Sometimes i'm smart........and sometimes I can't see the forest thru the trees.

That explaination makes PERFECT sense. THANKS!

 

[Justafordguy]

Good job Rustytruck.;D

 

[DirtDonk]

There's still something strange going on though GloNDark.
Since the clean air tube is not metered air, capping it or uncapping it should have no effect on metered air into the carburetor.

Have you tried simply putting your finger over the clean air tube while it's running? Opening and closing the tube while it's idling to see what happens?
I'm curious if this alone is your issue, or if there isn't some hidden gremlin related to it somehow.

Good luck. Interested to hear how it gets resolved.

Paul

 

[MarsChariot]

The clean air tube coming out of the air horn on the 2100 does nothing except supply air that isn't dirty to the choke tube, as has been explained. If the engine truly runs better with it unplugged...well, the air filter must be completely clogged or something! More likely that something else is going on that looks like it is correlated with the unplugging of the fresh air tube.

 

[BigStu]

You guys are awesome. There is still hope for me too as long as I have internet access

 

[GloNDark]

So I dug into this further last night. I bought a replacement choke tube kit that had the clean air, and hot air tube and installed. It would start but the choke wouldn't opperate. Once the truck warmed up it ran great.

So I pulled the carb off and dis-assembled the choke on the workbench. Even though I just rebuilt it, it was filled with dust, gunk and crap. So as described earlier, the hot air tube, even if it's in the little cast box that is on the header will still pull crap in. Cleaned and adjust the choked fully, installed the clean/hot air tubes and presto.

Choke functions as it's supposed too
Runs fine when warmed up.

My "guess" is the choke was sticking closed with the air filter on and plugging/unplugging the clean air tube effected it somehow. But again it's just a guess as i never really found the full explanation.

 

[gnsteam]

You dont use bungs on the headers. The tube going down to the exhaust manifold is just a heat exchanger. It has nothing to do with exhaust gas. Your Choke clean air tube is just the fresh air in. Use a piece of rubber hose and connect to the steel tube running down to your header. Wrap a couple of wraps of steel tube on the out side of the most convient header tube and run that same tube up to the choke cover. The up to the choke side of the piece should have some fiberglass sleeve on it to keep it hot. There is a vacuum leak inside the choke cover that sucks the air through the tube you added. This way filtered air comes from the top of the air horn of the carborator down the little tube. The wraps around the hot header heats up the air and is sucked up into the choke cover. When the choke gets this heated air it sences the heat and allows the choke pulloff to turn off the choke and close the vacuum suction inside the choke cover.
The stock manifold has a piece in it making the heated air chamber. It is not open to exhaust gas.
I hope that helps

Thanks Rusty. I was just about to post a thread with questions as to what the tube is (Choke clean air supply tube) going down into the area of the exhaust manifold on the rear passenger side of the engine. So far I hadn't be able to location where this attaches. Tonight I'll be taking a closer look at the manifold. I did notice the hot air tube attached to the choke housing, so I'll be tracing it back to the manifold as well.

What a great site. I learn something new every day.

Fred