Is the choke tube system for a '65 WCFB carburetor open to exhaust gas? I am experiencing very hot air (exhaust gas?) pulsating at the exit of the upper choke tube where it connects to the choke cover on the side of the carb. This does not seem correct to me. I understand the choke tube circuit to begin at the top of the carb with a rubber line attached to a clean air tube which connects to a choke tube within and near the bottom of the exhaust manifold. I think this choke tube in the exhaust manifold is only open at the ends with the other end connected to an upper choke tube which is a solid line terminating at the choke cover on the carb. If I am correct, I would not expect to feel pulsating exhaust gas at the carb choke cover...hence a ruptured choke tube in the manifold which would cook the carb choke mechanism which currently does not work. Am I correct? If so, how do I replace this choke tube in the exhaust manifold? Help appreciated. Cheers.
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Re: '65 WCFB choke tube assembly
Ron -
No, the choke heat tube that runs through the exhaust manifold isn't open to gases; your symptoms say that the tube has become perforated where it passes through the manifold passages.
The tube is installed from the bottom-up, and is staked in place at the bottom; you'll need to drive it out from the top and replace it - Paragon has them. -
Re: '65 WCFB choke tube assembly
I've replaced a few of these in my day, but on passenger cars. The model of carb can vary, as the same method for choke heat was used for many years (WCFB, QJ, AFB, Holley). I have always removed the manifold from the engine for this, but maybe someone has done it on the car (?). These are a vey inexpensive parts (were), but sure can mess up a choke when they break. You usually find the choke housing full of black soot and all gummed up (inoperable).
FWIW, I learned from the experience relative to the way the tube in the manifold is pinched to an "X" shape to restrict (slow down the air) long enough for it to be heated. I used the same technique to restrict tubes used with headers. I used aluminum tubing wraped (coiled) around a header tube and joined with a coupling to a "sleeve" insulated aluminum tube to the choke. Then, in order to get a full function (full close to full open choke operation), I had to pinch the tube with a vice grips in one or two places just enough to create a restriction, but not to close it off. I would practice on a scrap piece of tube to find the optimal setting for the vice grips. I would pinch the header tube once, then at full cold, adjust the choke to get full closure. Start the engine and allow it to warm up fully to see if I could get full open (not just by pull off, but sustained). If not, I'd pinch the tube again in a position 90 degrees from the first, and so on.
This was used with older style Hedman headers that did not have a choke tube provision.
Stu FoxComment
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Re: '65 WCFB choke tube assembly
You're LUCKY you discovered this now! Many simply don't think to question the integrity of the +40 year old fresh air tube that's press fit into the exhaust manifold...
As John Hinckley said it's probably the tube inside the exhaust manifold has perforated due to age/heat/moisture. That's NOT uncommon...
BUT, if the tube IS ruptured, you're essentially allowing red hot exhaust gas to penetrate and 'tickle' the seal integrity of your carb's choke assy. If that integrity fails, there's the possibility of HOT exhaust gas getting into your carb. Can you say KABOOM?
So, when you R&R the exhaust manifold to replace the fresh air tube, consider opening the carb's choke, cleaning it up and replacing any related sealing gaskets that are probably dry/brittle now...Comment
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Re: '65 WCFB choke tube assembly
Usually, in the course of troublshooting a cold weather hard start complaint, one of the first places you look is at the choke housing - specially if the choke is sticking open or partially closed. The presence of the black soot/scale/gummy scum in the housing will be very evident and indicate a perforated manifold tube condition which is allowing exhaust gases up through the choke tube. I have repaired a number back in the day, but none ever led to a dangerous condition, very poor engine operation, but not dangerous. In most cases, the choke was stuck partially closed causing a over rich mixture which in turn produced the black particulate matter mentioned above which plugged up the choke. It's like which came first; the chicken or the egg, or kind of self sealing/correcting, I guess.
Each one I repaired included a carb cleaning/rebuild along with new plugs and "tune up". They ran perfectly well after that. No permanent damage sustained.
Stu FoxComment
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Re: '65 WCFB choke tube assembly
My thanks to all for the responses. I am now on the path of replacing the in-mainifold choke tube. Looking down on the tube from the top it appears to bend to the rear inside of the manifold. This is not right as I believe it should be a straight length of tube. This along with the fact that the tube is not moving as I try to drive it out the bottom from the top is not a good sign. So, does anyone have a good technique for removing the choke tube? My instinct to use a bigger hammer has obvious issues. Cheers.Comment
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Re: '65 WCFB choke tube assembly
Ronald;
As we mentioned in previous post; you will be better off removing the manifold to get the tube out. It is Staked into bottom, as John noted, and you will have to grind/file or reduce this staking perhaps with a hammer and chisel until you can drive it out. Also, If it is burned in two, you may have to take it out in pieces through the downspout of the manifold with, obviously, the exhaust pipe disconnected. It is not necessarily an easy task, but you have to do what you have to do.
Stu FoxComment
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Re: '65 WCFB choke tube assembly
I replaced the tube on my 1963 exhaust manifold with the repro part. When removing, I drilled into each end and crept up in size until the wall of the old tube was thin enough to drive out.
After cutting out a section of the tube inside the exhaust manifold I drove the old tube inside from each end to remove. This is a very clean way to remove the tube.
The new repro tube has a flare on one end so I installed it from the bottom so the interference fit is at the lower hole in the manifold. To make sure the top is sealed, I used JB weld and sealed from the inside of the manifold to protect against any external exhaust leaks.
When installing the assembly take the time to make sure the lower pipe that runs behind the manifold fits correctly. This may require slight bending so after everything is bolted the small pipe is completely inside the new installed tube. You want to pay attention to this so there are no leaks and the carburetor sucks through the tube and not around the tube because of leaks.
On the top side, the tube to carburetor adjustment is much easier to fine tune. The design is to suck filtered air from carburetor air cleaner through the exhaust manifold tube and to the choke housing. This is a calibrated vacuum leak that is piped directly through the choke circuit to a passage between the primary throttle blades..
Sorry for the long....Comment
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Re: '65 WCFB choke tube assembly
Tim;
Nice explanation. It's been a long time since I did my last change out, but I was sure to do it right I had to remove the manifold.
Incidently, when I was dialing in my AFB last year, I tested the draw on that tube with a Mityvac and it only pulled about 1 to 2" Hg - hot or cold, at normal or high idle. I was surprised. So, in the big scheme of things, it doesn't have much effect on the calibration. I was going to use an earlier choke housing with a air tube connection directly on it instead of the choke cover which would keep that system intact while using an electric choke. However, based on the results of that test, I eliminated the air tube for now (my goal was to reduce all sources of extra heat to the carb to deal with the percolation problem, and that was just one minor source).
I believe a number of Holley's installations use an air tube connected to the housing along with a manual or electric choke cover.
BTW, Good Morning! Don't forget to fly your flag today - 9/11.
Stu FoxComment
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Re: '65 WCFB choke tube assembly
Good morning Stu,
I was just looking at pics of 9-11 towers, what a mess. Makes me mad all over again.. I don't support the Florida Pastor but no victory building there, I don't think anyone will build it anyway...Comment
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Re: '65 WCFB choke tube assembly
Thanks to all for the great information. I now feel confident in making this repair.
As this was my first use of the technical discussion board, I gotta say this is by far the best way to learn of technical details not in the manuals.
Thanks again to all!
CheersComment
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