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Are you trying too be correct or are you having a problem? I have seen double springs, but do not know the application or reason. If you put a second spring in you will increase your foot pressure and may cause discomfort on long duration driving. If all is well, let it be. Dennis
Although the factory installed only a single spring, a double spring is a good idea. If one spring breaks, the second one will still pull the throttle closed.
FWIW: Racers are required to run double springs. It helps prevent grenading an engine in the event a spring breaks or comes loose.
I drove the car today for the first time after installing an original professionally restored carb. Before ever hooking up throttle rod I tested it to make sure no problem with gasket interference. Every thing works like silk. While driving today it stuck a couple times at about 1500 rpm and once about 2000 rpm. If i tapped the pedal down or put toe under pedal and lifted slighly it came right back to 800 rpm. Thats why i thought the spring might be a little weak. It never did that with the other AFB i had on it but when I put the correct restored one on I did have to turn the throttle rod about 3-4 turns to reach the nylon placement hole
Although the factory installed only a single spring, a double spring is a good idea. If one spring breaks, the second one will still pull the throttle closed.
FWIW: Racers are required to run double springs. It helps prevent grenading an engine in the event a spring breaks or comes loose.
Can help wear out the shaft holes in the Holleys and lead to a vacuum leak and the need to rebush! Basically you want each spring to be able to shut the throttle, and to not add excess tension! And the Big Toe technique (haven't heard that method used in awhile!), but you still have your big toe lift the pedal back up trick in an imperfect world, if all else fails!
PS everyone with single springs should take the spring off and shove the throttle over on the carb (engine off naturally), and if you insist on single springs, you should practice the big toe maneuver!
Last edited by TCracingCA; Feb 17, 2016 at 07:40 PM.
Can help wear out the shaft holes in the Holleys and lead to a vacuum leak and the need to rebush! Basically you want each spring to be able to shut the throttle, and to not add excess tension! And the Big Toe technique (haven't heard that method used in awhile!), but you still have your big toe lift the pedal back up trick in an imperfect world, if all else fails!
PS everyone with single springs should take the spring off and shove the throttle over on the carb (engine off naturally), and if you insist on single springs, you should practice the big toe maneuver!
Thought of tying string from steering column to gas pedal also
Double check that the pedal rod isn't binding on the underside of the aircleaner housing at full throttle. Mine stuck after a carb rebuild due to, I think, the new rubber bushing on the rod at the carb raising it just enough to bind under the aircleaner. It stuck open when I accelerated hard for the first time. What a thrill! I had checked for clearance after the install but apparently not in the full throttle position. It was not an original aircleaner so it might have sat lower on the carb too, reducing clearance.
Last edited by dkleather; Feb 17, 2016 at 08:27 PM.
I tried double springs. It was too much tension, so went back to one. Besides that the Holley I'm running has spring around the throttle shafts anyway. Just a safety matter.
As I looked closely at my photo a few minutes ago I noticed that the nylon spacer and washer look a ltitle crooked to me. it looks as tho the angle of the rod going into the spacer may be more than 90 degrees. This combined with a new spacer may be causing just enough drag to keep throttle from closing all the way upon deacceleration. Does this seem logical to anyone? Might try to get rod more at correct angle and lube spacer with silicone lube. Doe this make any sense?
Disconnect the spring (engine off of course) and work the throttle arm. Gently see if there is any resistance to it closing. If there is, disconnect the linkage to the accelerator pump and try again. Those pumps can sometimes stick in the hole in the lid. Something is sticking. You just have to keep disconnecting linkage until you find where it is. IF everything is disconnected from the throttle shaft and it still sticks, you have gasket interference with the primary throttle blades.
Verne
As I looked closely at my photo a few minutes ago I noticed that the nylon spacer and washer look a ltitle crooked to me. it looks as tho the angle of the rod going into the spacer may be more than 90 degrees. This combined with a new spacer may be causing just enough drag to keep throttle from closing all the way upon deacceleration. Does this seem logical to anyone? Might try to get rod more at correct angle and lube spacer with silicone lube. Doe this make any sense?
IT does look like it's angled but I doubt the surface of the linkage rod inside the nylon bushing would bind. Is the linkage rod attached to the throttle linkage arm from the firewall on the outside or the inside?
As I looked closely at my photo a few minutes ago I noticed that the nylon spacer and washer look a ltitle crooked to me. it looks as tho the angle of the rod going into the spacer may be more than 90 degrees. This combined with a new spacer may be causing just enough drag to keep throttle from closing all the way upon deacceleration. Does this seem logical to anyone? Might try to get rod more at correct angle and lube spacer with silicone lube. Doe this make any sense?
I agree, it doesn't take much friction to prevent that last little bit from closing.
A couple areas to check on the AFB carbs is the guide lugs around the accelerator pump shaft (see picture)...one side can wear and the shaft can then operate at a cocked angle and prevent smooth return to idle.
A second bad spot is the peened over part of the throttle shaft (red circle in second pic) -- that can work loose and even though the flat plate attached to it goes all the way back to the stop at the idle screw the looseness prevents the throttle plates from completely closing.
IT does look like it's angled but I doubt the surface of the linkage rod inside the nylon bushing would bind. Is the linkage rod attached to the throttle linkage arm from the firewall on the outside or the inside?
Disconnect the spring (engine off of course) and work the throttle arm. Gently see if there is any resistance to it closing. If there is, disconnect the linkage to the accelerator pump and try again. Those pumps can sometimes stick in the hole in the lid. Something is sticking. You just have to keep disconnecting linkage until you find where it is. IF everything is disconnected from the throttle shaft and it still sticks, you have gasket interference with the primary throttle blades.
Verne
Will be checking all this out today...will post with any results I come up with.
A couple areas to check on the AFB carbs is the guide lugs around the accelerator pump shaft (see picture)...one side can wear and the shaft can then operate at a cocked angle and prevent smooth return to idle.
A second bad spot is the peened over part of the throttle shaft (red circle in second pic) -- that can work loose and even though the flat plate attached to it goes all the way back to the stop at the idle screw the looseness prevents the throttle plates from completely closing.
Frankie thanks for your help. I will check those today but if I find a problem in those areas I am gonna be mucho pissed offo. $500 restoration and total rebuild should not have these type problems.
I'm not sure when Chevrolet when to dual throttle return springs, but I think it was in the mid-seventies. They use an inner and outer spring and between the two, the spring pressure is about the same as the earlier single springs. This is what they typically look like...
Anyone that drives their car regularly and has had the single spring break (after dropping a date off late at night) and go screaming through a neighborhood at WOT in 1st gear will appreciate a little back up. It may only have taken 5 seconds to reach down and kill the engine, but it sure did seem like a lifetime... at the time!
Dennis
Great ideaa for safety!!!
