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My '64 300 hp engine runs beautifully. The choke, however, doesn't seem to work properly. The kicker is the car starts perfectly and has a smooth idle at about 700-800 rpm even when ice cold. Normally I would say forget it, but I'm afraid I'll lose flight judging points because the choke doesn't operate properly. What's worse is I'm in that gray area between bowtie sign-off and flight judging as I've signed up for bot. Because of that I don't want to mess around with the carb (original). My feeling is bowtie is more important and the flight judging was an afterthought after a bunch of you fine folks suggested it would be a good idea. Nevertheless, this choke is still somewhat of a mystery. Any guidance would be appreciated. David
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Re: Midyear Choke Question
Your '64 High Performance engine has essentially the same Carter AFB as the Special High Performance engine in my '63. The choke system has a "choke vacuum break" that partially opens the choke valve after a cold start. A vacuum port in the main body of the carburetor continuously draws air through the choke vacuum break. It draws filtered air from the air horn through the exhaust manifold heater and into the choke housing where it pulls on a small piston with a linkage to the choke valve and thermostatic spring. Over time the piston gets gummy and sticks, and the spring cannot overcome the friction to close the choke valve and set the fast idle cam when cold. It's not hard to remove and disassemble the choke housing for cleaning, but there is a very small O-ring that seals the vacuum passage to the carburetor body. I can't remember if this small O-ring is in the typical rebuild kit (available from Federal Mogul). If the chock housing has never been off or if it's been a long time, there's risk that the O-ring may not be salvageable. If you can obtain the O-ring, then I would definately remove the choke housing, disassemble it, and give it a thorough cleaning. When you reinstall it check all the various adjustments per the shop manual to insure everything is in spec, and the choke system should perform as designed.
Duke -
Re: Midyear Choke Question
Duke's suggestion maybe 100% correct and then again maybe not. You stated the engine starts fine and idles fine even when it is stone cold. Given that, it is possible the choke is working properly, but the high idle is not set correctly. I would check to see if the choke is closing when cold, before you take things apart. Remove the air cleaner, make sure the choke is open, step on the gas pedal or move the linkage by hand while watching the choke. If the choke closes then the piston "should" be OK. I would then check the high idle cam and adjusting screw to make sure it is properly set. If the choke doesn't close, I would then check to make sure the choke adjustment is correct. If the setting is close to what it should be, then go with Duke's suggestion.Comment
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Re: Midyear Choke Question
Thanks for two excellent posts. I checked the choke by kicking down the linkage by hand. I was hoping for an out of adjustment hi idle screw but I wasn't so lucky. It didn't move a hair. Moving the choke by handle and it was very tight. I guess the choke needs to be torn down and that problematic O ring replaced. Unfortunately it will have to wait a few months as I'm not going to touch it and risk giving any indication the carb was off of the car (bowtie disaster). Thanks again for the great advice. DavidComment
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I concur
You're right, Ron. The first thing to check is the operation of the choke, but eventually all old AFBs will get the sticky choke vacuum break syndrome, so I just jumped (prematurely) to the fix.
David - It sounds like you've got time. Why not go ahead and get the zip kit. Check out federalmogul.com. There's a good section on rebuilding the AFB in the '63 shop manual. Also, HP Books has an "All about AFBs" book that's available through motorbooks.com. I don't think it's very risky to remove and clean up the choke housing as long as you have the O-ring. Even with a thorough cleaning it may not be perfect. I think the thermostatic springs may go off calibration with age, but you can usually dial it in by going a little richer on the choke housing adjustment.
DukeComment
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Re: Midyear Choke Question
In the mean time try a little oil on all the choke shafts and linkages, sometines that does the trick until you can rebuild it.Comment
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Re: Midyear Choke Question
Yes I think I'll do that. I thought about a dose of carb cleaner but WD40 might be a better approach. Shouldn't hurt anything in any case. I'll post my results.Comment
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WD-40, not oil
Oil will rapidly collect dirt and gum up the works even worse. Use Gumout to clean things off, then a light spray with WD-40.
DukeComment
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Re: Midyear Choke Question
David,
I'm pretty confident you can improve your Flight Judging score without screwing up your Bowtie chances by doing what I write below; however, to be safe, you could talk with Carlton Colclough (say "Coke-ley") (team leader) about what you should and should not do.
I'm nearly 100% sure the little piston that Duke speaks of is "carboned up". It was THE problem on my '62 250hp and '64 300hp. You really need to:
1) Clean the outside of the carb with soap, water and a small brush.
2) Remove the choke housing and disassemble it.
3) Drive out the aluminum plug under the piston. (I use a small bent rod.)
4) Hone out the piston bore. (600 grit wet-or-dry sandpaper will do.)
5) Polish up the piston with the 600 grit.
6) Reassemble.
7) Adjust the carb as suggested in the other posts.
During Flight Judging, the setting of the choke (actual movement of the butterfly when you depress the gas pedal) will be visually observed by the judges. The idle will also be noted, as will ease of start. You're probably dealing with about 25 points out of 4500, so it's kinda important that this works correctly.
You should be able to do all of the above such that no one can tell you've touched the carb, other than the cleaning. The judges really don't want to see a dirtball of a carb (or any other component), so clean it regardless of what else you do. Pick screwdrivers that fill the slot so you don't nick the screws. The little o-ring is in the typical rebuild kit (e.g., a Hygrade), IF you need one. You're allowed to clean up the outside of the carb, but don't take off any crayon marks, stamps, etc., if you find any. Cold idle, as I recall, should be 1600-1800 RPM. Warm idle should be around 550. Check the service manual.
Good Luck!
Bob D.Comment
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Re: Midyear Choke Question
I'm making progress now. The piston was indeed gummed up but after a little 600 grit cleaning and WD40, she works like a charm. Last night when checking the check by setting it by hand, she was purring at 1600 at high idle and 600 and low idle.
This morning I kicked it down when cold but the butterflies didn't close. I think the spring in the choke assembly is the problem as I'm not real confident I installed it properly. It popped off when I was taking it apart so I didn't see how it was positioned. I will try to adjust it tonight. When that spring is cold, I assume it should be pulling the butterflies closed (?). The advice thus far has been dead on and I am most appreciative. DavidComment
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Re: Midyear Choke: More Tips
David,
You're hot on the trail! When you think the bore and piston are clean enough, they probably aren't (unless you popped the plug out and did a thorough job). If the butterfly is not opening completely the tube INSIDE the exhaust manifold may be toast, or the orifice in the carb body may be clogged with carbon as the piston bore was (or one of the external steel lines is ajar or clogged).
The bimetallic spring should push the tang to the RIGHT (clockwise). If the butterfly is STUCK closed with the engine warm, determine if it's the butterfly shaft or in the choke housing, then proceed to free it up. If the spring is putting pressure on the butterfly in the right direction but the pressure is not diminishing as the engine heats up, the air flow is not right, as suggested in the first paragraph. If the butterfly gets TIGHTER as the engine heats up, the spring is in BACKWARDS.
I'm sure you'll be careful, but don't do anything that will appear to be more than cleaning, or you'll jeopardize the Bowtie thang!
Good Luck,
Bob D.Comment
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Re: Midyear Choke: More Tips
Thanks again for the great advice. The butterfly moves very freely after the piston was cleaned so now I am 99% sure that portion is working properly. Right now the butterfly is open when cold and staying open. Sounds like a spring position issue. All components appear to be in excellent condition including the tube to the exhaust manifold. I'll play around some more tonite but I now feel confident I can get it to work right while preserving the bowtie aspects of my sweet little coupe. Thanks again and hopefully tonite I'll post my final note. DavidComment
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Re: Midyear Choke: More Tips
Checked everything over again cold. Butterfly still wasn't closing enough to engage the high idle arm against the throttle. Then, I noticed the alignment line on the choke cover wasn't within the range of the tick marks on the other side. Set it right in the middle of the range and bingo - everything is working perfect. Idles at 1600 high and 600 at normal. Jumps right down with a little tap on the pedal. It's Miller time! Thanks to for all the help and patience. DavidComment
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