I have a stock Holley 4150 Holley Mech Secondaries with a bigger jet in it. It will stumble if you mash it to the floor until it hits 160 degrees(Neutral). I have the idle adjusted to 800 rpms. Below is my setup and I was wondering how close the carb is stock to getting the most out of my motor???? Accelerating at WOT its fine and when you let off the gas it backfires out the exhaust. Where should i start? I'm new to Carb's, what do i need to buy to check my AFR's?

"A" bigger jet? What does that mean?

You shouldn't be going WOT until the engine is fully warmed up.

Backfiring after you back off the throttle is from too-rich idle mixture.

Oops i meant i got a bigger squirter. So whats the first step i should take to lean out the carb?

Which squirter, primaries or secondaries?

To lean out the idle mixture, screw in the idle mixture screws. Is yours front-only adjustment, or 4-corner idle mixture adjustable?

To lean out the cruise mixture, put in smaller primary jets.

To lean out the WOT mixture, put in smaller secondary jets.

Those should be done in that order.

Awesome, thanks for the info. My mechanic adjusted the idle mixture screws but he set the idle to high so i turned it down a bit, does that mean its still getting the same amount of fuel from the higher idle? Because thats when i started getting the backfire.

If your under 2000 cruising it will stutter a bit like it cant hold the same RPM. Does that mean i need a power valve change or just a jet change?

What can i buy to check my AFR's? I'd like it to be around 12.5 at WOT

Go through the steps of this sticky http://www.thirdgen.org/techboard/ca...ey-tuning.html (Holley Tuning) for your tuning.

A wideband O2 sensor is the best way to do AFR. But, if you go through the steps above, you're going to be mighty close.

One last question, i have 1 " carb spacer on my intake. Does that throw off the engines low end and top end power? My cam is 2 degrees retarded. Will i have to adjust the carb for that? Thanks Five7

Many different things can affect carb tuning. If you go through the sticky, and use a wideband for WOT, you'll basically be tuning out those effects.

Carb spacers effects go something like this: Open spacers increase the plenum volume, therefore increasing top-end power at the expense of low-end torque. 4-hole spacers increase the individual venturi "signal", enhancing idle and low-throttle response at the expense of top-end power.

Retarding the cam shifts the powerband up. A retarded cam and 4-hole spacer would work against each other. But, as a tuning aid, may work together for better low-RPM response with slightly higher peak power.

"Retarding the cam shifts the powerband up. A retarded cam and 4-hole spacer would work against each other. But, as a tuning aid, may work together for better low-RPM response with slightly higher peak power."

So if tuned correctly a 4 hole spacer can increase low and top end?
I just dont understand with the contradiction. But ill look into some software from Moates.net. I used to have some good tuning equipment for my old tbi.

Is my stock ignition ok with my new motor? the only thing we changed was to a vaccuum advance distributor.