I have been having some real erratic idling issues on my 57 with the 2x4 WCFB's. At times it will purr like a kitten, and I can set the idle as low as 700rpm, then after a short while it will develop a rough idle, and begin shaking like a dog crapin peach pits! Is this just due to today's gas, or am I missing something? Tank is clean, new fuel filter and recent carb overhaul. I hate to start readjusting idle settings when I can sometimes get a great idle. Any ideas? The car runs fine at wot with no missing, but this idle bug just won't go away.

 

I'd put a vacuum gauge on it first thing and see if you have decent, steady vacuum at idle - you may be fighting the wrong problem:

http://findarticles.com/p/articles/m..._n8978956/pg_2

 

80% of all carb problems are in the ignition.

Centrifugal advance hanging up?. You got vacume advance? Maybe the can is shot. Dist shaft have a lot of side play? Makes the dwell 'go away'.

 

Most of the carb problems are really ignition problems. This could simply be after a prolonged idle a plug or two carbons up until cleaned up at highway speeds.

If you a have a bit more agresive cam that produces a lower vacuum, you may not even be on the idle circuits. This is easy to check on the WCFBs. Pull the small plate with two screws on the left front of the WCFBs. You can run the engine (temporary) this way to check if the metering rods are down in the jets.

You will see a "T" with the two metering rods hanging on the "T". At idle these should be all the way down into the jets. When you advance the throttle they will pick-up. There is a vacuum plunger on the bottom of the "T'...vacuum pulls the rods down...accerating reduces the vacuum and the "T" is pushed up by a spring under the vacuum plunger.

There are TWO DIFFERENT springs (weak for the low vacuum more agressive cam engines and stronger spring for the higher vacuum less agressive cam engines. The springs that come in the off the shelf rebuild kits are the stronger springs (many mechanics do not know this). Since you had a carb rebuild, check this.

If your carb rebuilder gives you a silent moment or blank stare when you ask about this, he has limited experience with WCFBs (as most do). The weaker (low vacuum) spring is called the "270 hp spring"

If the "T"is NOT down at idle you are not even on the idle circuit but idling on the venturi jets which will tend to produce those peach pit jerks you discribed.

Joe

 

Could be the metering rods need adjustment , to much fuel flow could make the miss after a while of idealing and need to be set in the jets more.

 

Check you heat riser to make sure it is opening. If it's OK it sounds like float adjustment to me. With today's gas you should ignore the float settings in the book and set the float drop to 11/16" primary 7/8" secondary then flip the horn over and close off 1/4" primary and 5/16" secondary...wouldn't hurt to block or restrict the intake manifold heat cross over either but if you do make sure you wire open the heat riser valve

 

My spec calls for 1/8" for primary float height...your car doesn't run lean with the 1/4" - no lean surge ?

 

Not at all it runs just fine