off idle hesitation, too much or too little fuel?

[sasilverbullet]

On my newly rebuilt 460 with a Edelbrock 1406, on a Edelbrock 2166 manifold, off idle under load it stumbles when you press on the gas.

I know how to adjust the springs/rods/jets and such, I'm just trying to determine whether to go leaner or richer.

What do you guys think?

 

[Kuato]

IMO try leaning it first. Also, how's the accelerator pump?

 

[oldhp]

I start by adjusting the accelerator pump to the longest stroke. With engine off look down into the carb, move throttle open, do you see 2 streams of fuel squirting? There will be one stream of fuel for each separate primary opening. If yes, go drive it. Fixed? Done. Not fixed? Look for vacuum leaks which would make engine run lean. Everything plugged that would suck air? Been there , done that. Its' almost always the little things that get you.

 

[Rob_Roy]

so it stumbles if you ease into it...what happens if you smack the gas pedal right to the floor?

accelerator pump is the easiest place to start. also see how much vacuum it pulls when idling in gear, and compare that Edelbrock's recommendation for the metering rod springs.

 

[Olas]

Its hard to diagnose over the internet but every time I've had an off-idle stumble on a carb'd motor its always been too lean..
Do you have a garage nearby who would hook you Upto the emissions tester for 2 minutes? Should only cost 5 at the most, or if you're friendly with them it'd most likely be free

 

[Yah-Tah-Hey]

Haven't had a wrench on a carb in 30+ years, but I would start with the accelerator pump. When you open the bores you are letting in more air so the mixture goes lean. Accelerator pumps are there to inject enough fuel into the air flow to keep the mixture from being too lean. The older vehicles were so very much easier to work on. Just tweak the idle screws and the pump setting and you were good to go.

 

[ARCOgraphite]

FIRST Make sure your dist setup and timing is good to go. IIRC, you have a vac advance/ vac retard dist. With the new (ahem) manifold and carb (sorry hate Edlebrock ex. Victor Jr) you may have many important things not connected properly like the dist porting and the PCV calibration.
IS a 1406 an AFB or AFV? These are NOT great carbs. I had a 65 buick nailhead and a 67 340 Skylark with the real AFB.
Always better off with factory performance stuff unless you are trying to make 2x stock power.
Does your idle mixture respond well? - if not look for vacuum issues too.

 

[SteveSRT8]

Originally Posted By: sasilverbullet
On my newly rebuilt 460 with a Edelbrock 1406, on a Edelbrock 2166 manifold, off idle under load it stumbles when you press on the gas.

I know how to adjust the springs/rods/jets and such, I'm just trying to determine whether to go leaner or richer.

What do you guys think?


You got it already, accelerator pump is likely where you start. If adjustable then set it up for a bigger squirt.

Note that on some large displacement engines you need a LONGER squirt instead of just a bigger squirt...

 

[sasilverbullet]

I love this forum! Accelerator pump was on the lowest setting, moved it one up and voila! All hesitation gone! Smooth...

I probably would have dorked around with the springs/rods for days...

 

[Olas]

Told ya so ;p

Ain't it great when you get the right answer, fast?

 

[Merkava_4]

Originally Posted By: sasilverbullet
off idle under load it stumbles when you press on the gas.


Your accelerator pump isn't working. If you don't know what an accelerator pump is, it's a squirt gun for fuel. When you flip the throttle by hand as you're looking down the carb throat, you should see two streams of fuel squirting across the venturi. The purpose of the accelerator pump is to counteract the overly lean mixture from all the air that's rushing in there when you open the throttle plate. Remember: fuel always lags behind the air; meaning, air gets there first.

PS. Ethanol in fuel ruins the accelerator pump diaphragm.