Holley Carb Fuel Slosh question

[chepsk8]

Been trying to get the carb on the Cobra set up as I like it.

Here the specs:

1988 5.0 stock long block
Edelbrock Performer 289 Intake manifold
Holey 600 D/P Carb
Crane HI-6 Ignition
Headers
Electric fuel Pump (CARTER)

Car mods so far:
Primary Jets extenders
Primary jets reduced for better A/F Ratio
Power Valve reduced from 6.5 to 4.5
Float levels tried all over the place.

Here are my two issues:
1. It still has a slight hesitation when hammering it from a stop or low speed. I hear this is common, and learning to "roll on" the throttle will make this invisible.

2. During hard stops, it sputters and tries to stall. I have tried to cure this with the extenders, different float levels. Has anyone here had this problem, and cured it?

Many Thanks,

Dan

 

[silverbluebp]

I've had the same problems with my 600 DP! I added the jet extensions, didn't change. Adjusted the float levels, didn't change. Added a dashpot.....Ta Daaaa!!
It doesn't die when braking hard now!!

 

[chepsk8]

SB,

Can you provide more info, part #, pics?

 

[thehueypilot]

Maybe you ought to switch to a vac secondary carb. The correct way to size a power valve is to hook up a vacuum gage with a long hose to full manifold vacuum and run it inside your car. Drive it around normally like the freeway with some hills on it and observe the vacuum readings. You should size the power valve to the lowest vacuum reading minus one step. For example if the lowest vacuum reading on your drive was 11, I would size your PV to a 9.5. As far as the hesitation it could be your double pumper is squirting too much raw fuel into the manifold. Try reducing the accel discharge nozzles size down two numbers from what you have now. Float level should be just a tick below the weep hole when hot. You should also add a bowl vent (plastic whistle) to keep the fuel from sloshing out of the bowl and down the carb throat during a hard stop.

 

[2bav8]

It's usually installed on vehicles with automatic transmissions, and it's there to prevent the vehicle from dying when you let off the throttle while driving; in a manual transmission vehicle, you have engine braking that keeps the vehicle running in those types of situations, where if you're driving along in an automatic-equipped vehicle, letting off the throttle will more often than not return the engine to idle, and sometimes to an RPM lower than what it will run at. These have been around as long as automatic transmissions have been available

A quick search on Summit Racing comes up with the following Holley Part # for a 4150 Holley: HLY-20-72

 

[chepsk8]

As far as the power valve, On the track, the car is usually wide open, or close to it.

The dash pot is an idea...

 

[chepsk8]

Tried the dashpot, no change.

The car has an electric fuel pump. Could too much fuel pressure cause the bowl to overfill during a hard stop?

Also, is this problem being caused by fuel slosh in the primary or secondary bowl?

 

[FORCED2DV8]

Fuel pressure should be bewteen 4.5 and 6 psi, Usually when i have that problem the float is sticking, or not adjusted properly, or the fuel pressure is too high, or the needle and seat are not sealing properly, try cleaning them and or replacing, make sure he float isnt catching and moves freely up and down.

 

[mfp4073]

you should be able to get the car to grab with a stab of the throttle. Its the cams that get you this....it basically leans out when you jab it open, the cam squirts extra fuel in there. They are cheap to get a set and just keep trying different ones until you get the result you like.

 

[D.Hearne]

Instead of jet extensions, you need vent extensions. And the hesitation is due to accellerator pump, not the power valve. Take the slack out of the accellerator pump arm to the pump lever. What's the list number on the carb ? Sure its a double pumper and not a dual feed, vacuum secondary carb?

 

[mfp4073]

yeah, what dhearne said, the decelleration (sp) bog is due to the fuel int he rear bowl sloshing forward and up the vent tube...then into the carb.

 

[zookeeper]

If you don't already have one, you need to install a good pressure gauge/regulator between the pump and carb and set it to 4-6 lbs witht he motor running. Then set your float levels, then make a vent extender with a length of hose. Simply connect the hose to both bowl vent tubes, then snip a hole in the highest point (middle) of the hose.

 

[chepsk8]

I just got a regulator, and will try it this weekend. Is there any way to make a baffle for the vent? I kinda figured it was on the secondary side, as the slosh will move the fuel against the metering block, no matter what level of the floats.

 

[chepsk8]

Also, what has been the way and measurement you used on the floats?



(had to post this, finally 2000!!! Not including all the fun over in talk...)

 

[D.Hearne]

I just got a regulator, and will try it this weekend. Is there any way to make a baffle for the vent? I kinda figured it was on the secondary side, as the slosh will move the fuel against the metering block, no matter what level of the floats.

Many Holleys came with thin brass baffles on the vent openings inside the bowls, some one may have tossed yours. They also offer plastic vent extensions that fit inside the bowls. Zookeeper's idea will also work.

 

[dennis112]

then make a vent extender with a length of hose. Simply connect the hose to both bowl vent tubes, then snip a hole in the highest point (middle) of the hose.

You can make this setup look trick by using old 90 degree spark plug boots on the vent tubes. The added height of the boot may be all you will need--if needed, you could still connect them together as mentioned above, but that probably wouldn't be needed.

 

[mfp4073]

I had problems with stuff like that fitting under my air cleaner. I never did solve it completely, but then I dont drive my car much these days.