Dead spot at idle
 

If I roll the throttle on to gain speed from a stop my car runs great. I have noticed today while playing around that if I just floor it from a dead stop it bogs and cuts off. Where do I start?

I thought you just had the car. other then belts slipping very much to your liking just two weeks ago!?

I have been driving the car thru break in and working the kinks out. I have changed all break in fluids and am now finally reaching the point to where I can beat on it a little

it sounds like the squirters are not working. and when you roll into the throttle it's okay, but when you stab it goes lean. pull the air cleaner and start the car and accelerate the throttle and see if the squirters are working, if not an easy fix is to order an accelerator pump assembly from Cliff Carb.
Jim

I have not been able to just drop the hammer from a dead stop because my builder, quick performance, and American Powertrain all told me to go easy the first 500/1000 miles. I have romped it from a roll a little but I have never just put it in first and dropped the hammer. I have passed those mileage milestones a while back and I changed all my fluids front to rear, greased everything, made sure all ujoint bolts etc were tight and went to a stretch of deserted highway. Did a few rolls like I have been with a little power shifting and that noise is getting better. Decided to just stab it from a dead stop and everytime I did it it just fell over and died. If I roll throttle on it will smoke the **** out of them thru 1-2-3 but just a dead stop mat gives me nothing. Honestly I have never had a double pumper. I have always had vacuum secondaries to mask crap like this but I am determined to learn. I would rather not watch a bunch of Youtube videos and end up screwing up my car trying every shade trees method. I just hope someone can point me in the right direction. As far as the belt squeal I got it worked out by using a belt the local NAPA old timer recommended. Stopped it cold

Figure out a way to lock out the secondary’s on the carb, maybe with some mechanics wire or a cut off section of a coat hanger.

You want to do this so you get the primary’s to work right first.

Start here, https://www.macsautoparts.com/holley...069e429ad7a77e

As BB said above read this:
https://www.holley.com/blog/post/acc...y_carburetors/

Your problem is all in the primary accelerator pump adjustment.

I agree with not running the engine really hard or WOT for the first few miles, but not 500-1000.

I would strongly suggest at 100-200 miles to pull the oil filter and cut it open, it will tell you IF you need to pull the engine back out or can start running it like you stole it!

There are a LOT of things to check when you have a HUGE stumble/hesitation/bog going quickly from idle to full throttle. The engine/drivetrain/vehicle specs and carb/distributor details would be helpful here......

I feel your pain with Youtube videos, I get ill trying to watch any related to carburetors especially Quadrajets. 99 percent of those folks need to shut the camera off and go as fast as they possibly can right back to their "day-jobs"!..........FWIW.......

I cut the 150 and 500 mile filter open. They were fine

What size is your fuel line and what fuel pump? Not that those will affect the idle to WOT dead spot but with 550 hp will affect your in motion high RPM performance.

3/8 and Holley 110 GPH. If it revved any faster I would have already blown it up

What do you have for a carb?

X2. didnt this engine have FI at some point? might be confusing it with another one... is it a box stock carb or been set up for your engine?

if its a traditional holley mechanical secondary double pumper, you should be able to just remove the link bar to the secondaries, no need to conjure up a coat hanger. thats how most mech sec double pumpers ive owned or seen operate the secondaries.

A Holley carb or any carb is not designed to perform well when doing a "gorilla stomp" at IDLE and expect the MASS FLOW thru the engine to have the correct fuel to mix with it.

There is always a time lag with the carb circuits.

The outside air does not even really start to move into the engine and without the air and intake signal to the carb.

Then you have the air restriction thru the air filter, (You are running a air filter, right?).

If you are trying to do this "Test" what purpose does it serve if you have removed the air filter and this car is NOT A DRAG CAR. .............WOT FROM IDLE. Chee-it.

There is a thing called PHYSICS that describes how the air and fuel works in a carb.
The accelerator pumps are there to be able to do transitions from normal cruise to passing speed or
higher rpm launches to ATTEMPT to move the car across the starting line quickly.

You should have left the EFI stuff alone as the engine dying when you do that "test"
and is telling you, it is not going to work.

If you disconnect the secondary throttles and run the carb as a two barrel carb you might get the thing to NOT DIE doing your "TEST" if you put a 50cc pump on the front carb and big squirters on the primary side. But now the carb will drive like chit when on the road doing normal speed vs load transitions.

Tom V.

i can "gorilla stomp" all my cars from idle with basically instant acceleration (& lots of tire smoke), there is no noticeable lag, hesitation, stumble or dying... mechanical holley double pumper with stock size acc pump on a mild built 455, using all 4's or just the primaries when i would disconnect the secondaries when i let friends drive it or to try & save gas.

same for cliff built Q-jets on a mild 400 or stroked 500+hp engine, or even a stock engine on home rebuilt qjets. maybe each engine can act different but i've never had any of those problems

Weren't you EFI?? With the Sniper I could tell you why it's doing that and how to fix it. There was a discussion about that in the EFI section with good explanation as to why.

If it's a carb, I'd need to know what carb.

Knowing ignition timing helps in this scenario to some degree.


But initial thoughts are simply a lean stumble. Very common when whacking the throttle as you create a big hole and not enough fuel to fill it is the simple explanation. A new combo will take some tweaking to make perfect.

This car needs to be taken to a mechanic to get sorted out.

I have the pink accelerator pump cam which is the second smallest. QUICK FUEL says it’s calibrated out of the box for a smaller engine and to up the cam. I ordered the cam kit. And no it doesn’t need to go to a mechanic. It runs fine you just can’t dead stomp it right now. As long as I roll the throttle on it’s almost uncontrollable on street tires

You should be able to fry the tires ( or at least one tire) from a idle !

If you flat out stop on it and the motor just dies with out back firing, then you have a issue(s) that are likely not carb related!