throttle spring tension

[John C.]

Hey fellas, just wondering about the correct throttle spring tension for a 65 300 hp 327 ( manual ). I have a new spring in place from LI supply attached to the correct spring perch. But the pedal tension is too weak, so much so that I added another ( incorrect ) spring just to have it stronger so I could drive it. Is it typical for the pedal tension to be rather light for this engine ?
JC

[Edward J.]

Re: throttle spring tension

John, I have seen this sometimes with the repro. springs. another problem is sometimes the throttle blade shaft will wear and cause the shaft to bind and not return to idle.

[John C.]

Re: throttle spring tension

John, I have seen this sometimes with the repro. springs. another problem is sometimes the throttle blade shaft will wear and cause the shaft to bind and not return to idle.

Ha, well you nailed it Edward. The tension is too light AND sometimes it won't come back to idle without tapping the throttle. I've been looking for a 3721 for 6 months now. I guess I'll just run 2 springs until I can find a carb to replace the incorrect AFB that is on the engine now. So what is the solution to acquiring the desired spring tension ?
JC

[Edward J.]

Re: throttle spring tension

John, Try another spring with bigger dia coils. or add another spring to fit inside the other coil spring.

[John C.]

Re: throttle spring tension

I can do that. I was thinking maybe there was another method being used that was closer to what was original. I've doubled springs on other cars for the same reason. Hope I didn't come across as an idiot, just thought there may be another OEM looking trick. Thanks Edward !
JC

[Edward J.]

Re: throttle spring tension

John back in the later70's GM use to use a double spring on the Quadrajet's for the reason that when the engine was running, the vacuum from the engine would be pulling the on the bottom of the throttle blades making the blades stick at times.

[Leif A.]

Re: throttle spring tension

I can do that. I was thinking maybe there was another method being used that was closer to what was original. I've doubled springs on other cars for the same reason. Hope I didn't come across as an idiot, just thought there may be another OEM looking trick. Thanks Edward !
JC

John.
Just remember to remove the second spring for judging...I forgot

[John C.]

Re: throttle spring tension

Thank you !
JC

[Stuart F.]

Re: throttle spring tension

I have had the same problem on my 63 L-76 (SHP) since new, and that includes on 4 different carburetors representing 3 different model AFB's (2 3461S's, a 3720SA and a 3721SB new replacement). I have had to use a second spring as well. Long ago I found a nice light weight 1/4" Dia spring that I hook to the second hole on the bracket that mounts to the LF 2 intake manifold bolts, then to the small hole below the accelerator rod on the throttle arm of the carb. It has served me well all these years, and is easy to remove and put back on in just a few seconds, with the air cleaner off of course. I too strongly dislike the non return to idle problem. Incidently, I also tried stronger white springs that used to be specified by aftermarket vendors for 63's incorrectly. I had to modify them to work and they too were not adequate.

So you see; it's not a specific problem for any certain model AFB, nor does it matter how old or worn it is. My current correct 3461s has had to have the primary shaft re-bushed as it was worn real sloppy such that the transfer slots in the 2 throttle bores were unequally exposed causing a lean surge condition. New bushings cured that, but not the idle speed condition. I still need the second spring.

Stu Fox

[Mike T.]

Re: throttle spring tension

John - I felt the single return spring setup was a bit light as well and on my 65 300 horse 4spd Coupe, I went with an aftermarket two-spring setup from Summit but for my L79 66 Coupe I wound up using a dual spring-inside-a-spring setup that I believe came from later year Corvettes. Sorry but it's been so long I haven't got any more info on parts numbers or applications. Here's a pic of that setup.

[Leif A.]

Re: throttle spring tension

John - I felt the single return spring setup was a bit light as well and on my 65 300 horse 4spd Coupe, I went with an aftermarket two-spring setup from Summit but for my L79 66 Coupe I wound up using a dual spring-inside-a-spring setup that I believe came from later year Corvettes. Sorry but it's been so long I haven't got any more info on parts numbers or applications. Here's a pic of that setup.

Mike,
That's exactly what mine is. Click below...

http://www.parts123.com/corvettecentral/dyndetail.pta?catalog=0000050g&ukey=10431