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I’m a novice when it comes to carburetors but I want to try and solve this myself if I can.
1964 327 300hp AFB 3721SB carb
I’ve read a bunch of related threads on the forum but still don’t quite “get it”.
In these pictures the engine is cold. I shot a video but I’m not sure if it will upload successfully. In the video I have the accelerator linkage fully open while turning the choke cover back and forth. Nothing seems to happen.
Can anyone tell me what I can do to get the choke operational? Like I said, I’m a rookie.
As always “Thanks in advance!” Current setting I made sure the coil hook is engaged with the tang on the choke piston inner lever.
Yes, you should be able to manually move the linkage. - it must be frozen. I have a divorced choke so I’m not that familiar with this type of self-contained choke, but it appears the spring center may not be keying into the choke link shaft when the cover is installed in place.
Yes, you should be able to manually move the linkage. - it must be frozen. I have a divorced choke so I’m not that familiar with this type of self-contained choke, but it appears the spring center may not be keying into the choke link shaft when the cover is installed in place.
There is a piston inside the AFB choke housing that can seize due to carbon fouling and this requires disassembly and cleanout:
The piston tang attaches to the coil and can make the coil inoperative.
Last edited by Frankie the Fink; 03-09-2021 at 08:16 PM.
There is a piston in the choke body that often sticks, possibly due to carbon corrosion. The piston is connected inside the black choke housing to the lever that you say won't move, so it's stuck. The weight of the piston helps pull the choke off as the springs warms and weakens. There is also a small hole at the bottom of that piston chamber that put's vacuum on the bottom of the piston to help pull it off. There is a tiny o ring in that vacuum hole, so look out for it when you take out the three screws that hold the choke body to the side of the carb. That piston MUST move freely for the choke to work.
There is a piston inside the AFB choke housing that can seize due to carbon fouling and this requires disassembly and cleanout:
The piston tang attaches to the coil and can make the coil inoperative.
Originally Posted by Birdman63
most likely cylinder is stuck. take off soak to see if loosen up.
Thanks guys. I’ll give this a try in a couple of days (supposed to be sub zero tomorrow 🥶 and then report back my findings.
👍🏻
There is a piston in the choke body that often sticks, possibly due to carbon corrosion. The piston is connected inside the black choke housing to the lever that you say won't move, so it's stuck. The weight of the piston helps pull the choke off as the springs warms and weakens. There is also a small hole at the bottom of that piston chamber that put's vacuum on the bottom of the piston to help pull it off. There is a tiny o ring in that vacuum hole, so look out for it when you take out the three screws that hold the choke body to the side of the carb. That piston MUST move freely for the choke to work.
I've seen those piston bores so crapped up that I had to remove the Welch plug on the bottom and scrub them with Hoppes #9 gun solvent and a brass brush like a rifle bore - no kidding.
I removed the choke from the carb and as many of you suggested, the piston is STUCK.
I soaked it overnight in a 50/50 mix of ATF and Acetone (see 2007 Machinist Workshop test below). Kroil is hard to find in my area. I also sprayed some Liquid Wrench.
The piston will now more up and down a little. Maybe 1/4” +/-. The piston is still really tight when it gets to the top.
What do I do next? I don’t see how to completely remove the piston to access the piston bore for further cleaning if that is what’s required.
Thanks!
Remove the flat head screw and pull the piston out the top. If it is too tight to move that far, you will have to remove the plug in the bottom and tap it out the top. Then when you get it cleaned out and moving freely, put the plug cap back in the bottom. In order to remove mine, I drilled a very small hole in the center of the cap, hooked a curved scribe into the hole and pulled it out. When finished, I covered the hole with a dab of JB Weld.
Once that screw (and attached lever) is removed, the piston can be rotated and you may find a spot in the rotation that will allow the piston to come out without removing the plug at the bottom. Also, don't forget the small o ring I mentioned earlier in the small hole where the choke tube fits up against the carb body to allow vacuum to assist in pulling the piston down as the spring warms.
Remove the flat head screw and pull the piston out the top. If it is too tight to move that far, you will have to remove the plug in the bottom and tap it out the top. Then when you get it cleaned out and moving freely, put the plug cap back in the bottom. In order to remove mine, I drilled a very small hole in the center of the cap, hooked a curved scribe into the hole and pulled it out. When finished, I covered the hole with a dab of JB Weld.
Once that screw (and attached lever) is removed, the piston can be rotated and you may find a spot in the rotation that will allow the piston to come out without removing the plug at the bottom. Also, don't forget the small o ring I mentioned earlier in the small hole where the choke tube fits up against the carb body to allow vacuum to assist in pulling the piston down as the spring warms.
Ok. I may have to remove the plug and tap the piston out through the top.It seems too tight to pull the piston out and I’m afraid of breaking the piston lever.
Yes I removed the small o ring as you suggested👍🏻
I have the same year car, same motor and same choke piston issue. I bought a used replacement off of Ebay and that's been fine so far but I'd still like to get the original back in working condition. Mine was repaired by someone before because the bottom cylinder plug was replaced with JB weld. I plan to drill out the weld and hammer the piston up from the bottom. Then I'll see if I can clean and brush the cylinder enough so it will work. I have replacement plugs so I shouldn't have to use weld on it this time. I tried soaking it in penetrating oil and boiling it in washing soda which were both recommended on this forum. Neither of those methods got it out. The weather is just starting to warm up here so I'll start a few garage projects again soon. I don't do much out there in the winter. Maybe after I retire I'll get a heater.
I have the same year car, same motor and same choke piston issue. I bought a used replacement off of Ebay and that's been fine so far but I'd still like to get the original back in working condition. Mine was repaired by someone before because the bottom cylinder plug was replaced with JB weld. I plan to drill out the weld and hammer the piston up from the bottom. Then I'll see if I can clean and brush the cylinder enough so it will work. I have replacement plugs so I shouldn't have to use weld on it this time. I tried soaking it in penetrating oil and boiling it in washing soda which were both recommended on this forum. Neither of those methods got it out. The weather is just starting to warm up here so I'll start a few garage projects again soon. I don't do much out there in the winter. Maybe after I retire I'll get a heater.
Hi Steve
i followed the advice from 65GGvert and drilled a small hole in the plug, popped it out and tapped the piston out. I’ll fill the hole with some JB Weld.
I’m going to do a little light sanding until the piston moves freely then reassemble🤞
I retired 2 years ago, bought the car, bought a 4 post hoist, and have been enjoying myself ever since! Learning something about the car every day.
I do not recommend sanding that piston or its cylinder, again try some firearm solvent; it is designed to eliminate contaminants from combustion...along with a brass brush.
Once you have the piston channel open cleaning it up is trivial.
Last edited by Frankie the Fink; 03-13-2021 at 06:41 AM.
After removing mine for the third time I sanded the piston and the chamber to free it up. The first two times it was very free until the car heated up and then cooled down and it would stick again. After sanding I've had no trouble for several years. It didn't seem to adversely affect anything.
03-09-2021, 05:42 PM
Another choke question
and then report back my findings. 
