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Hot air choke operation...65


Guest Im4darush
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Guest Im4darush

I know there are two tubes. One goes from the passenger side exhaust manifold to the choke housing, and the other from the air horn fitting down to either the manifold or the flap valve. I think its actually in the manifold on the 65. Anyway, I have noticed that the choke has not been opening all the way. I have to set it really lose and even then it takes forever until it comes completely off the fast idle cam. Started looking around and found that the tube going up to the airhorn is no longer connected at the manifold. Broke off right where it attaches at the manifold. Will this cause the choke spring to not unwind? I know they both work together so Im guessing this is the reason. The tube that goes to the choke housing is there and in good shape.

I cant see under the exhaust manifold where the tube broke off...is this just a heat tube, or is there actually exhaust flowing through that tube up to the top of the carb? If so, I now have an exhaust leak. Trying to figure out what my options are, and if I will have to pull the manifold.

I like original stuff, but electric choke may be in my future if reconnecting that tube becomes a pain.

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Only a problem if you're not pulling hot air from that tube that runs through the exhaust manifold and exits at the top. The metal tube and rubber hose that runs from the bottom of the manifold to the air horn on the carb is a fresh air supply. Without it, there's not too much to worry about, you're getting air at the bottom of the exhaust manifold, just not as fresh as desirable. Make sure there's vacuum to the hot air tube and there's no obstructions in the tube in the manifold then everything should go back to normal. Have you taken the choke housing off and cleaned it really well? They can get gummed up with exhaust gasses if there's a hole in the tube running through the manifold. If that's the case, look for a post by Tom Mooney that shows/tells how to bolt a hot air chamber to your exhaust - it's an aftermarket item sold to be used with tube headers.

Ed

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Guest Im4darush

Vacuum to the hot air tube that comes out of the choke housing correct? Not the fresh air tube from the airhorn.

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Guest Im4darush

I unscrewed the tube at the choke housing and there is no vacuum there at all. Im about to rebuild this carb so if it is all gummed up, that will take care of it. Thanks for that info, I did not know that was a make-shift vacuum port.

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I'm not the best person to explain it to you, but there's a little there coming from somewhere, or so I've been led to believe. Perhaps someone with hands-on information will chime in here. If you're rebuilding the carb, ports should be cleaned out. Did you find a rebuilding kit yet?

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Guest Im4darush

Have not found one yet, but I think I will take your advice and just call thecarburetorshop. The kits at the parts store are all universal and I have no clue if the materials used are ethanol resistant.

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When you call, ask for Jon and tell him that you're on the AACA forum and ask him as many questions as is necessary to satisfy yourself that you're getting what you need. He can also answer your question about your choke. I think the last time I tried calling him was on a Wed., Thurs, or Fri. and I got a recorded message that he only works on Mon. and Tues. Must be nice.

Be sure that you have the carb numbers off your carb. I'd hate to see you ask for a carb for your car then find out later that someone somewhere along the line has switched carbs on you.

Ed

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Guest clamshells

Inside the choke housing is a piston that blocks the vacuum once the spring relaxes so check for vacuum with engine cold.

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Guest Im4darush
Inside the choke housing is a piston that blocks the vacuum once the spring relaxes so check for vacuum with engine cold.

Interesting!!

Riv...my afb is the original 3921s that came on the car.

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When you call, ask for Jon and tell him that you're on the AACA forum and ask him as many questions as is necessary to satisfy yourself that you're getting what you need. He can also answer your question about your choke. I think the last time I tried calling him was on a Wed., Thurs, or Fri. and I got a recorded message that he only works on Mon. and Tues. Must be nice.

Be sure that you have the carb numbers off your carb. I'd hate to see you ask for a carb for your car then find out later that someone somewhere along the line has switched carbs on you.

Ed

"He only WORKS on Mon & Tues" THANKS A LOT ;)

Monday and Tuesday are communication days. Wednesday, Thursday, Friday, Saturday, and some Sunday afternoons are WORK days!!!

As to the choke operation:

http://www.thecarburetorshop.com/Automaticchokes.htm

And

http://www.thecarburetorshop.com/Heatstovefabrication.htm

And Ed, thanks for your referrals.

Jon.

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Jon,

Sorry about that. When I got the message that you only answered the phone on Mon and Tues I figured you were on the Lake of the Ozarks fishing on Wed, Thurs, and Fri. :rolleyes:

I'll be calling you next week. I have a question about carb choice for my '64. Original AFB, or a Quadrajet. I have the '66 manifold and a choice of three different Q-jet carbs - an OE '66, a service replacement '66, or a bigger carb of a '73 era Olds 455 that was used on a GMC motorhome.

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There should be a vacuum signal being delivered to the choke housing. That is what encourages the air flow thru the system.

The passage in the carb originates in a plenum exposed to intake manifold vacuum at the base of the carb. This passage often gets blocked up with hard carbon and must be cleaned for the system to work properly. Believe it or not, I have had good luck cleaning this passage on the car with a short length of sharpened metal coat hanger and a small drill. Sometimes, the carb must be removed because the passage is severely clogged. Dont forget the small rubber oring which seals the carb passage to the choke housing or the vacuum signal will be lost.

The fresh air source for the system, the metal/rubber line which runs from the carb air horn down to the bottom of the exhaust manifold, allows FILTERED air to enter the system. If this part of the circuit is eliminated the air which is drawn into the system will be unfiltered.

The after market heat stove Ed mentioned will work on a stock cast iron manifold as well as tube headers. Good luck,

Tom Mooney

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Guest Im4darush

Now that I understand that there is vacuum at the choke housing it's clear how it all works. Flow of fresh air is best so I'll pull the manifold and see what it will take to connect the fresh air tube.

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  • 4 weeks later...
Guest Im4darush

I have everything straight aside from the little choke pull-off deal inside the choke housing. Mine has the rod sticking up out of the hole but it does not budge one way or the other. If I understand this thing right, there is a little cylinder inside that gets pulled down as soon as there is a vacuum source thus slightly cracking the choke flap open.

Should I be able to move this rod up and down? It does not budge up or down.

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Guest Im4darush

OK after a bit of research I realize my piston is seized down in it's bore. Tried everything including soaking the choke body overnight and it does not budge. Any ideas? I saw on the web somewhere that efb choke housings are available for the corvette complete with piston. Wonder if these will fit my 65 afb.

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What did you soak it in? I'm betting that if you're using the correct stuff and you let it soak for a few days, you'll be okay. You probably need a dip bucket of carburetor and parts cleaner. The stuff that really stinks, not the spray on kind either.

post-50017-143142699277_thumb.jpg

"Have patience young grasshopper"

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Guest Im4darush

Soaked it in the dip bucket parts cleaner you speak of. It's stuck pretty good.

Will heating it do anything? Or more harm than good?

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Guest Im4darush

I think it's still a matter of time. Just let it soak until there crud floating or at the bottom of the pan.

Ed

I invited mr torch to the party. Few hot/cold cycles did the trick. Came right out! Even the cap fell out from the hot/cycles. Polished the bore and piston until it slid easy and put it all back together.

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