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Old 10-17-2012, 11:47 AM
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Hot Air Choke 2150 Motorcraft

I am at a loss here. The choke tubes are clear and clean from the carburetor fresh air inlet to the choke assembly itself. I blew some carburetor cleaner through it and it is all open.

Problem I am expericing though is the choke doesnt seem to get hot. There are no holes so I figure it is the heater element in the intake manifold is not getting hot. I thought maybe the exhaust cross over is blocked with carbon.

But I want to know what to check on this carb cause I can run the engine and put my finger over the fresh air inlet as well as the outlet into the choke housing and feel no suction or pressure. I figured this might use the heat of heater to cause the hot air to rise into the choke assembly sucking cool air from the intake in. But something is not working cause the plastic housing for the choke doesnt get hot it gets warm. The choke stays closed even while driving at 170 - 180 degrees and it only opens and goes to slow idle after I turn the engine off and let the engine get even hotter from sitting then the choke opens when I step on the throttle.

Anyone have any ideas on what to check? My 1978 shop manual`s are of zero use.

I tried something and it appears to work now but the choke tube from the intake doesnt get hot, the mounting plate with the heating tubes does get hot but the tubes by the choke are cool. I sprayed the spring down with some electronic`s parts cleaner that shrunk the spring to its coldest setting, I set the choke very lean but the choke plate closed and after about 5 minutes of running (engine was still warm a little) the choke plate opened more and more then tap the throttle and the cam switched to the hot low idle setting. I hope it is fixed though but I will find out in the morning when the engine is fully cold.

I just dont understand why my shop manual says to hook up a flow meter to the fresh air intake port mounted to the carburetor and measure the air flow. I felt no air flow at all with the engine running through that circuit.
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Old 10-20-2012, 09:56 PM
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Air should be flowing into the choke cap, aka you should feel vacuum at the choke cap port. It's been a while since I rebuilt a 2150/2100 so bear with me.

Does the choke open fully if you manually push it off the cam? Do you maybe have the cap wrapped around a turn and a half by accident?
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Old 10-24-2012, 12:16 PM
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One of the mounting studs that holds the choke housing to the throttle body also houses a small vacuum passage. There is a gasket that goes in between. Make sure this path is not obstructed. This is how fresh air is drawn into the system. Here is a picture:

Click the image to open in full size.
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Old 11-29-2012, 01:53 PM
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Quote:
Originally Posted by wyckedcombo17 View Post
Air should be flowing into the choke cap, aka you should feel vacuum at the choke cap port. It's been a while since I rebuilt a 2150/2100 so bear with me.

Does the choke open fully if you manually push it off the cam? Do you maybe have the cap wrapped around a turn and a half by accident?
The choke works fine. It moves freely from cold closed to hot open. The problem I noticed is with the engine running the choke stove tube to the choke housing doesn't get hot. I was running the car after 5 minutes the exhaust manifolds were warm to the touch and this choke tube was cold.

I'm thinking my choke crossover in the intake might be carboned up, not sure if this can happen but I know my she port under the carve was.

As far as vacuum goes there is no suction but I don't know if it should. This remand carve lacks quite a bit of feature that my original had, such as a check valve bowl vent operated by the accelerator pump. My new one doesn't have a check valve.
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Old 12-01-2012, 05:54 PM
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Hot air is pulled into the thermostat by suction originating in the carburetor. With the engine running and inlet to the thermostat removed, the vacuum should be detectible by feel, or maybe try a small piece of paper and see if the vacuum holds it in place.

If there isnt any vacuum, the black cover could be cracked (sometimes it is hard to see), the small two hole gasket is missing or out of place, the channel through carb to venturi port is clogged with carbon, or the gasket under the black cover is missing.

The missing bowl vent control linkage wont have any effect.
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Old 12-02-2012, 11:46 PM
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Quote:
Originally Posted by Rusty_S View Post
As far as vacuum goes there is no suction but I don't know if it should.
This was explained in my previous post, and correctly re-iterated by 46yblock.
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Old 12-11-2012, 11:48 AM
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I took the choke housing off the carb and checked everything everything is fine and not obstructed. I put my finger on where the piston would go for the older style choke housings on the inside, with the engine there is quite a bit of vacuum from this port. Enough to make a very loud hiss.

I put the choke thermostat in and bolt the cover down and when I check the fresh air inlet I get no vacuum there. I even hooked up my vacuum gauge and nothing.

I disconnected the choke stove tube that connects to the choke housing itself and ran the engine and the brass choke tube fitting has no vacuum there. I took the system apart yet again and checked the passages for the choke housing to the brass choke tube fitting and all of them are wide open and not obstructed.

I cant explain it but the choke tube doesnt get hot because air is not being drawn in but yet there is vacuum and there are no blockages. I also checked for leaks and spraying the choke housing with the engine running caused no change in the engine running.

If there was vacuum coming from the choke housing fitting for the choke tube I would say the choke stove is rotted, but since I am getting no vacuum from this fitting but yet there is vacuum with in the choke thermostat indicated by the loud hissing and suction from the bore towards the front of the housing on the inside I am at a loss of what to check.

If I could find a pure electric choke conversion for a 2150 carb I might consider that. But I rather keep this setup since it worked great when I got the car but now its like my only option would be to pull the housing off the old carb and swap them out and see if that makes a difference. I know with the old carb the choke worked great but with this new one it never worked.
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Old 12-11-2012, 12:19 PM
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Puzzling! Everything works but it doesnt work. It sounds like you have made a good attempt at trouble shooting. I doubt even with a leak in the choke area that spraying with a flammable would result in increase engine rpm. But maybe so.

Once I had the very small hole plug right next to the bottom housing mount screw come out. Result vacuum leak. Filled with epoxy. Another time the large plug on the side of the small plug was loose, leaked and needed to be reset. Has a cracked black cap been absolutely ruled out? One more thing, Sometimes the cap retaining ring does not seat and fix the thermostat to the underlying gasket. If that is the case add another gasket. It is also possible that the wrong gasket is in use under the black cap. Some can obstruct the inlet.

Something this simple surely we can figure out .
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Old 12-11-2012, 01:23 PM
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I haven't ruled out a cracked cap but this cap is the new one that came with the carburetor. I put the old factory one on when I got it new. I swaped them out about a month ago with no change.

I had two gaskets but when tightened one would squeeze out and I feared it was causing a leak. I left just one on but tightened down fully I can still turn the choke thermostat cap if using some force.

With how strong a suction the vacuum has (about 20-22 inches) I think the flameable spray would have been picked up but I need to go through everything to verify. The choke has vacuum but the pick up fitting for the choke tube has none like its blocked off but its not. The small gasket appears to not cover the port but there are two small ports for vacuum to the choke tube, one slightly larger than the other.
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Old 12-11-2012, 05:18 PM
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It sounds like you may have narrowed it down to the thermostat cap gasket.

Even though it is a long shot as to cause, hopefully a picture will come up showing the two plugs I was talking about.

holeplugs.jpg photo by 46yblock | Photobucket
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Old 12-12-2012, 02:24 PM
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Quote:
Originally Posted by 46yblock View Post
It sounds like you may have narrowed it down to the thermostat cap gasket.

Even though it is a long shot as to cause, hopefully a picture will come up showing the two plugs I was talking about.

holeplugs.jpg photo by 46yblock | Photobucket
I picked up some gasket material today and some Hb weld steel stick, made two gaskets for the choke thermostat cap. I checked the cap itself for cracks and leaks which it had none. I stacked double gaskets and mounted then I was getting 5 inches of vacuum at the hose to the carburetor horn. I also found out the horn fitting tube was blocked by some yellow corrosion so it appears now the choke tube to the choke thermostat is getting nice and hot now.

Now I just need to install the 1969 alternator bracket and jb weld the splits and cracks in my aircleaner housing.

Thanks for the help wouldn't have narrowed it down without it.
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Old 12-12-2012, 02:24 PM
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