[andy dunn]

Well fiddling around with brake bias, I noticed that I could stall my engine out if I attempted threshold braking. I called Holley and here is what there tech support says is happening

I guess under heavy deceleration, one of the fuel bowls, I forget which one, pushes gas to the wall and up the vent stack. This then falls into the carb and floods it out.

They gave me a couple things to try.

1. make a crossover vent tube
I did this by copying one of their 4WD carbs. I then testing the hard braking again and it might of helped a little, but I was still able to stall the engine.

2. lower float bowl fuel level 1/8"
I have not tried this suggestion yet...I can't figure out how I would know the level has dropped an 1/8" inside the bowl?

Has anyone had this stalling condition under hard acceleration or deceleration? Am I on the right track or are there any other ways to fix this?

thanks for your time

Andy
http://www.cobralads.com

 

[Wes Tausend]

Andy,

I don't know much about the stalling condition but I think you can just set and observe the center of the float drop about 1/8" with the bowl off. Fuel level should follow accordingly. I don't think the distance is critical within 1/16".

 

[Qwik 1]

Just a thought............. but dragracers use secondary jet extentions because the fuel climbs to the rear of the bowl exposing the jets to no fuel on hard acelleration......... could the opposite be true on hard braking. the engine wants to run on only the primaries but the fuel is now climbing the walls of the front of the bowl exposing the primary jets to no fuel. Solution jet extensions for the primary side..........................maybe?????????? Just a thought. Brian

 

[CobraEarl]

If you are running vac assisted brakes, you can have a leak in your diaphram.

earl

 

[DragonSnake]

If lowering the float makes it worse, then I think Qwik 1 has your solution. Otherwise, ???

 

[mikiec]

Had the same problem. Lowered the secondary float and it has helped tremendously.

Another thing you can do is to add a longer whistle in the secondary float bowl.

Mike

 

[Frank Messina]

There are a couple of things to look at in sorting this out. First, get rid of that pipe connecting the vent tubes. That is incorrect for that carb. If you were going to do something like that the connecting hose still has to be vented to the atmosphere otherwise you're going to be sucking fuel back and forth between the bowls. No good. First, go back through your set up to make sure you have the following: 1. No kinks or tight bends in your fuel lines 2. Min 3/8" (1/2" better) fuel line from pump to regulator. 3/8" line from regulator to carb or -6 if your using AN fittings. 7 Lbs fuel pressure at all times( if you have one of those pressure guages mounted at the carb you'll just have to live with what you see at idle. 3. Set your fuel level so that it is just at the bottom of the sight plugs. Before we had clear plugs we set it by adjusting so that fuel just dribbled out of the holes with the engine running. Install a long plastic whistle vent in the secondary metering block. It's easy, they're cheap and they pop right in. This will keep fuel from running out of the vent and eliminate any external hoses. On our drag cars the whistle goes on the primary side and there is no fuel spill at all even with wheel stands. Set your idle mixture at all four corners. Also check your vacuum signal with a gauge. If you have weak vacuum the engine will run unevenly which can sometimes be difficult to hear if you have a cam with a lot of overlap. Make sure you don't have any vacuum leaks anywhere and set your idle for highest vacuum and rpm. Then set your idle. You might want to experiment a little with your idle settings, raising in 50 RPM increments to get the best balance for your use. This should give you a pretty strong running piece.

 

[andy dunn]

Hey, thanks kindly for all the tips. I wanted to clear up a few things I have already tried and then outline three things I might try next.

Vac Assisted Brakes
I am using just regular manual brakes so I don't think that comes into play.

Vent Crossover Tube
Holley tech support suggest the tube and it actually is slotted. They suggest maybe six 100/1000th holes but instead I slotted it with a dremel to copy their Avenger 4X series so air can get out of the vents and into the atmosphere. Here is the Holley Truck Avenger used for hill climbs etc. You can see the slots they add to the top of the tube in their pic.



Fuel Line
seems straight and no kinks

Pressure
My fuel pump is a Holley Red with 5lbs. at the carb. I don't really think I need 7lbs since you can calculate your fuel needs at wide open throttle here
http://www.prestage.com/carmath/calc_fuel.asp
With roughly 520hp at flywheel, I need 43 gallons per hour at WOT. The simple Holley red pumps 97 gallons an hour freeflow, 67 GPH at 5 PSI which I have at the carb.

Fuel Level
those pics above are old and I abandonned the site plugs since I could not see anything I used the drip out method.

Four Corner Idle
I checked this a few months ago and actually 1.5 turns out, factory settings right out of the box, produced the highest vacuum pull. It was 13lbs when I checked

Vent Wistles
Here is my holley model
http://www.holley.com/HiOctn/ProdLine/Products/FMS/FMSC/0-80528-1.html

It comes with vent whistles standard on both sides. I have seen variety packs at Jeg's and there is a chance that I might be able to go one size longer.

WHAT TO TRY NEXT
I think I will try some of the following suggestions next

1. MEASURE 1/8" LESS
Thanks Wes and Mikec. I have set the float measuring like this before so I will try it again and this time just chop of an 1/8

I guess I will try one side of the carb and then the other and then both and see if that helps.

2. JET EXTENSIONS
Qwik 1, I found these at Jeg's and have been tempted to buy them but I am still not sure if these will help or not but I may give them a shot. They seem to be more for a starvation condition rather than a flooding one.
http://www.jegs.com/cgi-bin/ncommerce3/ProductDisplay?prrfnbr=1900&prmenbr=76

3. FUEL LEVEL CONTROL KIT
If all else fails, I may break down and try this Moroso kit. It seems to turn your bowls into a mini fuel cell. The problem is they are pricey at $50 each and you need a pair. They claim "Ideal for extreme conditions such as hard acceleration, cornering and braking".



thanks for the tips and there is my current plan I will let you know ow it works out

Andy
http://www.cobralads.com

[ April 13, 2002, 01:06 AM: Message edited by: andy dunn ]