Holley Carb Problem

[Tommy]

I have a new 750 cfm Holley 4160 (vacuum secondary) on my small block engine. I went through the standard tuning procedure, set the idle at 900 RPM and everything checked out ok. But, with the engine warmed up and the choke off, the idle will not return to 900 unless I punch and release the throttle sharply. If I ease off the gas at a normal rate, the RPM hangs at about 1500 RPM. I've got one strong return spring on the throttle lever and another on the carb itself, but it still hangs up. Can anyone suggest a cause of the problem and a solution?

[SCOBRAC]

Two things can cause your problem. A) the main idle / throttle screw could be hanging up on the lever / carb base plate causing it to not fall closed all the way after the heated body / baseplate has warmed up (warmth=expansion) Or B) you have the idle circut improperly adjusted.. The screws are located on either side of the carb body, with a vacuum gauge close one, then the other adjusting for optimum idle / vacuum..

Regards,

[A Snake]

Just for grins, try getting the motor warmed up, get it to hang up, turn off engine and go look at every bit of the linkage closely. The screw hang up sounds like a good bet to me. Also consider a very slightly bent throttle rod (goes through the base and has the butterflies on it.)

Last, look at the angle you have the return springs on compared to the direction of travel. Don't be afraid to put a pretty healthy spring on. I've "Solved" several "hang-ups" this way. couldn't find the hang up, so I put on a bigger spring and voila!

Al

[mr0077]

And if you have an electric choke, check the fast idle cam, make sure it is dropping out of the way.