Last weekend I fired my rebuilt 454, sporting a holley 750 vac. secondary carb. During the break in, I noticed when the choke plate is closed a bit the idle speeds up a bit. This was while the engine was at operating temperature. My friend suspected a vacuum leak. We checked but found no leaks. Is this normal or do I need to increase the jet size?

Does this happen just when you close the choke flap? Closing the choke should engage the fast idle cam. If so, that's your problem... the fast idle cam will open the throttle blades a bit and cause a higher idle.

If it happens when you cover the choke horn and has nothing to do with the choke flap, you might want to make sure the idle mixture screws are adjusted properly.... don't worry about the jets yet. They really shouldn't come into play at idle.

And yep, it could be due to a vacuum leak. They can be tough to find sometimes. Make sure the intake bolts are tight. And that all extra carb ports are plugged... I forgot one a time or two... Make sure the carb base gasket is sealing to the intake properly. Make sure everything that should be covered by it, is.

Good luck! smile.gif

chris

FWIW, original jetting for a '70 LS-6 is 70 prim, 76 sec. This is per the '70 Chevy factory service manual.

Sounds like you need to adjust your choke