Throttle plate spring preload

[FABombjoy]

I had my throttle apart years ago and I'm wondering if I have the spring preload wrong. If the throttle is closed slowly the idle switch can keep the plates cracked just slightly. Give it a tap and it goes back to normal.

By hand I can preload about 90 degrees easily, or with some effort about 270 degrees. Anybody know what it should be? Manual doesn't seem to have any details.

[David T]

There is no "preload". If the throttle can't return all the way to idle either something is sticking or bent, worn, or dirty. There are 2 springs, one right on the throttle shaft and another in the throttle spool. If you aren't returning all the way look for play in the quadrant link, the piece between the throttle arm and the throttle spool. The ends of the quadrant link wear allowing a lot of excess play.

[Elvis]

with or without the engine running ?

vacuum !

[FABombjoy]

There has to be a preload, either a quarter turn or 3/4 turn. Nothing is bent, etc. If I can rule out how much is appropriate at the throttle body then I can move to other parts of the system.

[Drive Stainless]

I think i had mine at 3/4 turn on the throttle, and then I removed the top spring from the throttle spool assembly to provide for a lighter pedal.

[FABombjoy]

I'm thinking I'll try 3/4 and see.

I figure if the throttle body spring tension from the idle microswitch is enough to crack the throttle plates then the 1/4 position can't be right.

Setting the throttle rod so that the cable spool spring pushes the throttles closed seems to be an exercise in futility - I can make it idle well hot or cold but not both.

The BAE piping confounds the issue just a bit. Since the throttle assembly can float around, even if the throttle rod is dialed in perfectly to assist with closing, all it takes is a rev or two to shift things just enough to knock the idle off again.

If the pedal seems heavy I'll try removing the top spring as well. Thanks for that suggestion!