Infamous Holley deadspot

[Mom's Car]

I have an off idle deadspot on my 850 with mech secondaries.

Anyone have this same issue? I thought it was resolved when the locked accelerator pump on the secondaries was replaced. Apparently I thought wrong. I thought about just swapping to a quick fuel carb. Any thoughts?

[CrazyDavey]

Greg usually, and I mean usually, it's the primary accelerator pump lever adjustment. Here's what Holley says..

 

The most common cause of a stumble is not having an adequate accelerator pump shot. The first thing to do is to look at the discharge nozzle and make sure you are getting a good strong pump shot. If not then you need to inspect the pump diaphram for a hole or tear. You will also need to make sure that the pump passage is clear from any trash or debris. First you will need to check the adjustment on the pump. To do this you will open the throttle all the way (WOT). Push the pump arm lever down and then adjust the pump override spring to obtain .015" clearance between the pump arm and lever. If you are having a stumble and no black smoke out the tailpipe then you will need to increase the shooter size. If it stumbles and you are getting black smoke from the tailpipe then it will be nessasary to decrease the shooter size.

 

My experience is you just need to play with the lever adjustment, some like that .015 clearance, some don't...

 

Dave

[Mom's Car]

I will take a look see........thanks.......Greg

[John Burns]

There are bunch of Holley videos on youtube- I didn't quite understand the "adjust the pump override spring to obtain .015" clearance between the pump arm and lever" because it is spring loaded- this vid gives a nice visual of how to do the adjustment:

[kc8oye]

i have that same dead spot.. i managed to get rid of most of it by changing my pump jet. what was left I covered up with a slightly richer idle mixture.. one day when i get back to it I'll try some different pump cams.. i only really notice it when I stab the throttle to WOT from a dead stop.

[Andy's Auto]

Greg, lots of variables on the root cause so a no answer to a few questions will as inportant as a yes. First, where is the motor idling. Lots of times a big cam and a loose convertor needs the throttle opened so far you expose the transfer slot under the blades. Pretty simple fix. Pull the carb, drill a 1/16th hole in each front throttle plate so you can physically drop the idle speed screw to get the slot on to of the blades.

 

Second would be timing. One thing that a big block does not have going for them is thier addiction to initial timing. The down is too much leaves the nose of the starter on the ground from the engine trying to spin backwards or just flexplate teeth laying oin the ground.

 

Third is attacking the accelerator pump. Volume, shooter size, cam selection, and lever adjustment all come into play. Not enough or too little too late gives you that wonderfull powervalve or baseplate gasket blow out. Too much gives a wisp of black smoke and a huge bog.

 

The idea is to get any chassis mods to work the car must react in synch with the suspension. Look at a few of Crazey Davey launches if you want to see art made in front of your eyes. Ye old geezer sits there at idle, stabs the gas on the last yellow. The car pulls the fronts up just a bit AS the car goes forward. His gal is quickly becoming a Master Tuner. And the best part is most if not all of this years vids are in 100 degree heat. much harder to launch a full bodied car in the heat as opposed to 65 degrees.

 

When playing at the track the first thing I work on is getting the car to go from a foot to the floor launch. I sit there at 900 rpm waiting for my last yellow then try to kill the cockroach under the pedal. The problem I have with my Bu is tearing the rear tires off past the 60 foot when the suspension unloads. But I think I fixed it but I have not been to the track at all this month. Heading out weds night,

 

Andy