cold start/choke issues? What to look at?

[rcarlisle]

Ok, I'm trying to determine what's happening on cold starts.   Truck has started from mid March to now (end of May) just fine.  Cold weather or hot.  Mash the gas 3 times (like all old carbed cars), turn the key and it fires really quickly.  However, it is cold natured for a while.  And no apparent fast idle.   I can live with it, but also think it could be better.  What do I need to be looking at on the choke side?  Linkage side? I have looked in the reference section but that confuses me a bit and usually you guys explain it better in real terms.  Search "choke" didn't turn up what I thought I need.

I don't have photos but can get.   It is a replacement engine, so I'm not sure if they put everything back.  Carb is not pretty - if I were replacing things that were working, I'd probably replace with a newer one.  But it seems to be working well other than cold starts.

I know it is missing the metal heat thing on the exhaust manifold that would attach to the riser and the heat tube that goes to choke if mine is supposed to have it.   81 F 150, 302.  

And in most cases, I'm not averse to not having all the emissions and extraneous stuff.   So it's ok if it's missing if it's not necessary.   Just would like to get cold starts a little better and not have to sit and futz with the throttle for 3- 5 minutes so it will take gas and go.   Starts fine, just won't take gas when cold or a few minutes ("Aw she's just cold natured").

Is it cold enough for the choke to really operate?  60s in the mornings, 80s in the afternoons.  

[Gary Lewis]

If your engine is “cold blooded” then you need some choke.  And you probably don’t have enough at the moment.

However, without the heat tube there’s no way for the choke to know how warm the engine is getting - unless you have the electric-assist choke that has a wire to it. Do you have a wire?

But even if you have a wire it doesn’t mean the choke will work correctly. In fact, it probably won’t as most of those only worked in a narrow band of temperature.

So to have it work correctly you will need to replace the hot air tube. Dorman has a kit for that which most part stores sell. Or you could replace the choke cap with an all-electric one. That’s not as good as the hot air tube but it is workable.

[LARIAT 85]

rcarlisle wrote

I know it is missing the metal heat thing on the exhaust manifold that would attach to the riser and the heat tube that goes to choke if mine is supposed to have it.   81 F 150, 302.

 

If you still have your stock carburetor (Motorcraft 2150) then YES, it is supposed to have that heat tube. In fact, you should have two tubes and a wire running from the choke to the alternator.  Without those tubes in place, your choke is not going to work correctly.

It would help if you could post a picture of your carburetor - particularity on the choke side - so we can see what you have.

rcarlisle wrote

Is it cold enough for the choke to really operate?  60s in the mornings, 80s in the afternoons.

Yes, you better believe it!  The air/fuel mixture should be set when the engine is at normal operating temperature, and that would be about 200 degrees.  If you did that, there is no way your cold engine is going to run smooth without a choke.

[rcarlisle]

Thanks for the quick replies.   I'll try to get some photos this evening when I get home so you guys can guide me.   And see what is really there.  The carb looks a lot like what's for sale on the internet.  But that heat tube part worries me a bit.   I'll look up that Dorman kit and see what all is in it.  I'd like it to work better, but it does work now.  So I can't complain too much, I guess.   Just want betterer.

[rcarlisle]

I found the diagram again and it's starting to make more sense, as I knew it would.  I don't remember it having a wire and did look for that last night as I remembered reading about a wire somewhere.   I'll try to get photos this evening so you guys can dissect what's there and what's not.   I hope it isn't missing too much.  

[Rusty_S85]

Three times?  proper setting for a carb is one hit of the throttle to floor to set the choke and it should crank up and stay running.

It might take some tinkering to get it to that point but that is how it should work when proper.

What you need to do is check your choke make sure it is fully closing when cold.  Then you need to check the choke pull off.  First you need to see how much vacuum your engine makes at idle.  Then while engine is cold not running unplugged the choke pulloff vacuum line and attach a hand vacuum pump and pump it to the vacuum that your engine makes.  This is where you now adjust your pull off to be slightly open but not too much.  Some engines will like more some will like less.  This will determine how well your engine stays running or if you have to attempt starting multiple times.

This is actually a fairly easy thing to fix with OE carbs, the thing I could never resolve was the off idle stumble which is an accelerator pump issue.  On mine I moved to the largest squirt setting possible and it fixed most of the stumble but its still there.  Reason why I will be glad to dump the OE carb on my new engine build.

On high speed cold idle there will be a screw on the passengerside if I remember right that sets your cold idle speed.  Mine was set at 2,500 rpm which is way too high I turned mine down to 1,500 rpm which is just right for a cold start.

The heat riser that you are talking about is this the one that goes to the aircleaner?  If so you dont need that mine hasnt had one for years after rotting off.  If you are talking about the stove that is inside the manifold near the collector then yes you will need that as even the electric chokes were only electric assist to help open quicker in warmer weather but mainly relied on hot air.  You can correct this with some tubing and screw clamp it to one of the exhaust manifold tubes.  Attach one end to your choke and attach the other end back to the base of the carb air horn in the back for its fresh filtered air source.

[rcarlisle]

Yeah, I know what "proper" is supposed to be.   But this one ain't proper for sure.  

Thanks for all the information you included.   But I can tell you in all honesty, I'm not that inspired to fix this thing.   It does start and run.   It will start on one pump, just usually sputters out.  Probably better than 90% of the trucks on FB?.   You guys here are that last 10%.   The upper echelon.  

If the choke would close up some, it would probably stay running.   If I can get the choke plate working somewhat, I'm sure I'll be happier.  If not, it's like an old car or motorcycle - just have to let it warm a bit more.   Usually I just keep my foot on pedal to give it a fast idle while I get me adjusted and seat belt on, etc.  

As for your off idle stumble, when I worked for the state motorcycle program (stay with me), the majority of our Honda 250 cc Nighthawks and Rebels had a stumble off idle.   On some investigation, turned out the ones that didn't stumble had a bigger idle jet.   My solution for the ones that stumbled was to put a #4 brass washer under the top of the needle to shim the plunger needle up a bit.   Made 300 bikes run better in NC.   There is probably a similar solution for the truck carb - figure out how to richen it up between idle and that acc pump squirt.   The Hondas had an honest-to-God accelerator pump on them.

 If I could get to the carb to study it better, this choke thing would be a lot easier.  When I get photos tonight, I will be able to study it all a llittle closer.  But there are still a lot of moving parts behind the choke pot thing.  Thought about buying a new carb, but till I figure out if all the stuff is there, it might not fix it.  

[rcarlisle]

Here's photos - I  took 21 in all, but won't post them all - only as needed.  Let's take a look to get started on figuring out what is here and what isn't.







What is the capped red thing in this photo?  It rotates down to this position when throttle is fully opened.



Any insight you guys can provise will be helpful.  

[Gary Lewis]

Houston, we have a problem.  Your choke doesn't have a connection on it for a wire, so doesn't have a provision for heating electrically.  Given that, w/o the hot air tube it will never work correctly.  If you give it enough choke to make it start well it'll take forever to come off and the engine will run very rich, if at all.

I can see several options:

Fix the hot air tube and the cold air supply.  This would be best.

Get an electric choke cap.  I think the Holley ones fit the Motorcraft.  This isn't as good as hot air, but it'll work.  I have an electric choke on Big Blue.

Convert to a manual choke.  There are kits for that which replace the choke cap and have a cable, like a throttle cable for a lawnmower, that runs into the cab where you can control it.

[rcarlisle]

Yep after our posts yesterday and when I looked at photos, I saw it was a mess of things missing.  

And ya know, the the truck will start quickly like it sits.  Just have to be easy on giving it gas to start with.  And that's from March til now.   What will happen in January may be a whole other story.  

I grew up with cars of suspect nature and that sound of mashing the gas a few times is almost as much of the starting process as turning the key.  

The manual choke idea has crossed my mind.  

I guess for now, I'll have to let it ride and deal with it later.  Maybe the Dorman kit.

Thanks for the input.

[LARIAT 85]

You are missing both choke tubes and that is not the original carburetor.  The one you have on your truck is made for a vehicle with an AOD (Automatic Overdrive) transmission.  You can tell by that linkage attached to the throttle lever.  

This is how the thermostatic "hot air" choke originally worked on your truck:

Clean, filtered air from the air cleaner is pulled through the "fresh air" tube (a rubber hose that is connected to the carburetor air horn and attaches to an aluminum tube) and into the bottom of the choke stove chamber on the exhaust manifold, where the air is heated up when the engine is running. From there, the heated air goes back up through the insulated "hot air" tube (attached on the top of the choke stove chamber on the exhaust manifold) that connects to the choke cap. As the air gets hot, it closes the spring in the choke cap, which allows the choke plate to open up as the engine warms up to run on a leaner mixture.

Anyway, this is how the thermostatic hot air choke originally connected to the exhaust manifold:





I think it would be easy to fix your choke issue and get your truck running much better.  First, you need to purchase one of these:

https://www.amazon.com/Dorman-HELP-03840-Choke-Stove/dp/B000COB3W8


This simple, cheap kit (about $10) is designed to bypass the choke stove chamber on the exhaust manifold and replace the stock choke tubes completely. The kit comes with a length of coiled up aluminum tubing that you can easily bend by hand, the tubing insulation, the hardware to mount the tube to the choke cap, and a little "dome" with a hole in one end for the tubing to push into. This dome clamps to the exhaust manifold or header pipe to trap the hot air when the engine is running and routes the hot air up to the choke cap.


Here is a picture of the universal Choke Stove Kit on my own truck. It's a Ford 302 with an Autolite 4100. The Autolite 2100/Motorcraft 2150 will hook up the same way:





The factory setup had a "fresh air" tube that routed from the carburetor air horn down to the bottom of the choke stove chamber on the exhaust manifold. This location provided filtered air because this area is located on the "filtered air" side of the air filter once the air cleaner is in place. I drilled a second hole on the other end of the dome that came in the Choke Stove Kit so that the hot air going into the choke cap would be filtered, more like how it originally was set up in the first picture. You can see where mine attaches to the carburetor air horn by the rubber hose right behind the choke cap.

The universal Choke Stove Kit doesn't use the "fresh air" portion of the hot air choke at all. It's actually a great way to control the choke - much better than any aftermarket electric choke would.  Unlike electric chokes, the thermostatic choke works in lockstep with your actual engine temperature.  

[rcarlisle]

LARIAT 85 wrote

You are missing both choke tubes and that is not the original carburetor.  The one you have on your truck is made for a vehicle with an AOD (Automatic Overdrive) transmission.  You can tell by that linkage attached to the throttle lever.  

This is how the thermostatic "hot air" choke originally worked on your truck:

Clean, filtered air from the air cleaner is pulled through the "fresh air" tube (a rubber hose that is connected to the carburetor air horn and attaches to an aluminum tube) and into the bottom of the choke stove chamber on the exhaust manifold, where the air is heated up when the engine is running. From there, the heated air goes back up through the insulated "hot air" tube (attached on the top of the choke stove chamber on the exhaust manifold) that connects to the choke cap. As the air gets hot, it closes the spring in the choke cap, which allows the choke plate to open up as the engine warms up to run on a leaner mixture.

Anyway, this is how the thermostatic hot air choke originally connected to the exhaust manifold:





I think it would be easy to fix your choke issue and get your truck running much better.  First, you need to purchase one of these:

https://www.amazon.com/Dorman-HELP-03840-Choke-Stove/dp/B000COB3W8


This simple, cheap kit (about $10) is designed to bypass the choke stove chamber on the exhaust manifold and replace the stock choke tubes completely. The kit comes with a length of coiled up aluminum tubing that you can easily bend by hand, the tubing insulation, the hardware to mount the tube to the choke cap, and a little "dome" with a hole in one end for the tubing to push into. This dome clamps to the exhaust manifold or header pipe to trap the hot air when the engine is running and routes the hot air up to the choke cap.


Here is a picture of the universal Choke Stove Kit on my own truck. It's a Ford 302 with an Autolite 4100. The Autolite 2100/Motorcraft 2150 will hook up the same way:





The factory setup had a "fresh air" tube that routed from the carburetor air horn down to the bottom of the choke stove chamber on the exhaust manifold. This location provided filtered air because this area is located on the "filtered air" side of the air filter once the air cleaner is in place. I drilled a second hole on the other end of the dome that came in the Choke Stove Kit so that the hot air going into the choke cap would be filtered, more like how it originally was set up in the first picture. You can see where mine attaches to the carburetor air horn by the rubber hose right behind the choke cap.

The universal Choke Stove Kit doesn't use the "fresh air" portion of the hot air choke at all. It's actually a great way to control the choke - much better than any aftermarket electric choke would.  Unlike electric chokes, the thermostatic choke works in lockstep with your actual engine temperature.

THAT IS EXCELLENT EXPLANATION!   Let me pose a few questions.   THe Dorman kit as it comes - it straps onto a hot pipe with one metal hose coming out.   Since it doesn't hook into the actual exhaust, isn't it clean hot air?  Why do you need the filtered air?  With that said I really like how yours seemingly works with the original setup.   I think your explanation is the best I've seen so far for me.  

I don't really understand the two hoses in the original setup.  Is the original setup tapped into the exhaust flow?  Does the filtered air push that much?  

[rcarlisle]

Check this photo.  Am I understanding how this works?



Dorman would be similar without the air from air cleaner?  Unless modified as you did yours?  Looks as if the Dorman would fit loose enough to draw cold air in around that housing.

Yours looks great, but my question is "is the juice is worth the squeeze" running the extra tube?  I'm not discounting it, just wondering. I see an extra heater tube kit from Dorman on Amazon as well.  I may order all that and see what I can cobble up.    

I'm actually getting stoked to choke.  LOL

[rcarlisle]

Ok, I have ordered the Dorman kit to try to make this work.   When I do the heat tube, what else am I going to have to address?  I'm worried something isn't right in the linkages triggering the throttle.   With the truck not running (ambient temp), when I open the throttle to WOT,  the choke plate is not moving.  Linkage moves on choke side, but doesn't really seem to move the choke plate.  Just wondering what's going on with that?  

 I'm not sure I see how adding the tube will correct that condition.   I WISH I had the carb in my hands to be able to see up close how everything relates.  But not ready to go down that road just yet.  

[LARIAT 85]

The hot air does *not* hook into actual exhaust.  There is a hollow tube-like compartment built on the side of the passenger stock exhaust manifold.  It serves as a *chamber* to collect hot air generated off of the exhaust manifold.  The choke tubes pressed into the top and bottom of the chamber (hot air rises) to circulate the air from the filtered side of the carburetor (when the air cleaner is in place) to the choke cap. Inside of this chamber would have been a mesh filter that would also serve to hold the heat in the chamber.  It would look like this:

https://www.npdlink.com/product/fitting-and-screen-choke-stove-pipe/143995

The reason for the fresh air tube is so the choke cap will only see clean, filtered air.  The air you pull into the choke assembly will ultimately make it's way into the engine.  So ideally you would want to use filtered air.  Some of the older carburetors like my Autolite 4100 used a piston in the choke cap to operate the choke.  If it pulls dirty air, it can possibly jam up the piston and render the choke useless.

(If you do not run the fresh air tube, make sure to cap off the connection under the carburetor air horn so that it does not pull unfiltered air into the carburetor.)

That is why I tapped the second hole in the other end of the [chamber] dome and ran another tube up to the carburetor air horn connection.  I purchased the filter above and pushed it into a slighter larger copper tube, and placed that assembly under the [chamber] dome.  Then I pushed the choke tubes into either side of the [chamber] dome so it mimicked the factory setup as close as possible.  It has been like that for about ten years now, and I haven't had any problems.

[rcarlisle]

Ok, again thanks for the EXCELLENT EXPLANATION.   Somewhere I was reading yesterday it made out like the exhaust manifold was providing DIRTY air and the routing of cold air hose was fixing that.  

I ordered the Dorman and an extra heat tube kit to be able to try to replicate your setup with my iron manifolds and Y pipe down pipe.   Have to figure out where to best mount it up.  Drill a new hole in blank end, install hose.  Figure out how the mesh filtering between the two.  

Now to just hope the linkage actually works correctly when all that is done.  

[LARIAT 85]

Glad I could help you.  

The Motorcraft carburetor you have is the best, simplest 2-barrel carburetor ever made.  And the thermostatic choke works better than any other choke style.  You will find that when you get it tuned right and the choke set up correctly, it will run almost as good as any fuel-injected vehicle.  

[rcarlisle]

Here's a good video on basic choke operation - mine has a vacuum thing on back of all this choke stuff, but this shows me how it all is supposed to work together.

https://www.youtube.com/watch?v=DuPOJuWFC5s&t=134s

[LARIAT 85]

The beauty of keeping the stock Ford carburetor on a stock engine is that the Ford engineers already did the work and made all the adjustments for your specific vehicle.  Unlike an aftermarket carburetor that is designed to work on any engine, the stock Ford Autolite and Motorcraft carburetors are engineered to run on a specific engine size and engine family, automatic or manual transmission, vehicle size and weight, and even specific emissions equipment.  

When you purchase a rebuild kit, you will get a rebuild sheet telling you exactly how to make all of these adjustments to get it back exactly where it should be for an easy installation.  Only minimum adjustments to the choke and the air/fuel mixture screws will be needed.

[Rusty_S85]

rcarlisle wrote

Yeah, I know what "proper" is supposed to be.   But this one ain't proper for sure.  

Thanks for all the information you included.   But I can tell you in all honesty, I'm not that inspired to fix this thing.   It does start and run.   It will start on one pump, just usually sputters out.  Probably better than 90% of the trucks on FB?.   You guys here are that last 10%.   The upper echelon.  

If the choke would close up some, it would probably stay running.   If I can get the choke plate working somewhat, I'm sure I'll be happier.  If not, it's like an old car or motorcycle - just have to let it warm a bit more.   Usually I just keep my foot on pedal to give it a fast idle while I get me adjusted and seat belt on, etc.  

As for your off idle stumble, when I worked for the state motorcycle program (stay with me), the majority of our Honda 250 cc Nighthawks and Rebels had a stumble off idle.   On some investigation, turned out the ones that didn't stumble had a bigger idle jet.   My solution for the ones that stumbled was to put a #4 brass washer under the top of the needle to shim the plunger needle up a bit.   Made 300 bikes run better in NC.   There is probably a similar solution for the truck carb - figure out how to richen it up between idle and that acc pump squirt.   The Hondas had an honest-to-God accelerator pump on them.

 If I could get to the carb to study it better, this choke thing would be a lot easier.  When I get photos tonight, I will be able to study it all a llittle closer.  But there are still a lot of moving parts behind the choke pot thing.  Thought about buying a new carb, but till I figure out if all the stuff is there, it might not fix it.

Thats a possibility for mine.  But the 2V 2150 carb on my '82 is the same one on my '78 351W, they are both 351cfm 2150s.  No stumble on my 351W but stumble on my 302.  Cant be too much fuel from the accelerator pump as when I increased the squirt it made a positive difference in reducing some of the stumble.

But I am getting away from all that, aftermarket fuel injection is where I am going myself.  Everything works on my carb but the stumble is what got me and the more I think about it I rather have aftermarket fuel injection with way more adjustability that will actually change with elevation and ambient air temperature.