KurtAKX

I have a 454 TBI installed on my 350.

I currently have the throttle screw set far enough open that I have 0 IAC counts at 600 RPM.

When the engine is not running, the throttle shaft rotates silky smooth.
The pedal action is nice and smooth.

When the engine IS running, the throttle blades act like they are being "sucked shut"- grabbing the throttle lever on the side of the throttle body to give it a twist, it's like you have to initially twist pretty hard to overcome the vacuum. Once you twist the throttle that initial bit it moves easily- it's just cracking the throttle that's miserable.

It feels sticky at the pedal as it does by hand.

My engine is running 600 rpm and 30-32kPa-ish manifold pressure (LT1 takeout cam)

So far I've tried opening the throttle via the screw (thinking the TBI was just shutting too far and binding the butterflies in the bore) and I've also tried bumping my idle timing down several degrees with the hope that I'd make a little less idle vacuum and it'd be easier to overcome that initial tough spot.

Anyone else have this problem?

Anybody got any good ideas to get rid of that unpleasantness when you first open the throttle?

RBob

iTrader: (1)

This is usually caused by the throttle shaft bores being worn. Bushing them is really the only solution. If the wear isn't too bad you can cheat and use some thin wall brass tubing such as that from a hobby store. Still need to drill out the bores a little, but it does work.

RBob.

dctrumpet

iTrader: (10)

What intake are you using right now?

KurtAKX

I am using the overpriced GMPP TBI unit, machined out to 2". My TBI is the newer 454 style with the wide passages. Because the GM intake doesn't have a large enough footprint to seal off those passages, I have a Jegs 1" TBI spacer plate intended for the later 454 TBI. It seals my iac passages on the TB, and with no IAC passages in the spacer itself, it seals to the intake.

KurtAKX

I also have the throttle linkage spaced up a little over 1" to account for the second gasket and spacer. I couldn't do that very easily at the back of the bracket, so I fabbed up a bracket off the rear face of the head out of 1/4" steel plate to rigidly mount the rear part of the bracket up 1" higher. My geometry measures within 2mm of stock in every dimension, so I don't think linkage is my issue, especially since I feel the stickiness in the throttle itself with the cables detached.

dctrumpet

iTrader: (10)

Sounds like a potential vacuum leak at the shaft.

KurtAKX

Vacuum leak at the throttle shaft results in sticky throttle shaft?

dctrumpet

iTrader: (10)

If there is play/wiggle in the shaft this can cause a vacuum leak and that "play/wiggle" can cause a binding of the blades

dctrumpet

iTrader: (10)

You're in Decatur? I'm in Jacksonville

KurtAKX

If I bring my TBI over, can you re-bush it? I'd prefer not to do it on an exchange basis because I already have a truck-style 700R4 linkage welded to the 454 shaft.

dctrumpet

iTrader: (10)

Yes, I can do that

dctrumpet

iTrader: (10)

217-473-4998 give me a call!

Tc2youngblood

Can I call you I have some question about my 454 newer TBI

dctrumpet

iTrader: (10)

I believe we have been emailing back and forth the past few days? Tyrone correct?