Hi everyone
I have a 70 440 duster with an 871 bds blower. I have a pair of 600 edelbrocks on it now. Runs pretty good just having and issue after I drive it a while it tends to stall when i am at a light and go to take off, or if i am coasting slow then go to go and once in a while when I drive up an incline. I checked the floats they seem correct. I am wondering should I look into a better carb setup for my car. Its main intent is just crusing around locally.
what are your recommendations?

You should be able to make those carbs work. Others are running similar carbs on blown 440's. If it was me, with a blown 440 I would run a pair of holley 3310's.

any other suggestions

maybe it is boiling the fuel so it needs a insulating spacer under the carbs but on my car i found the fuel pressure to be too high when that happins.

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Check the springs under the step up rod pistons idling in gear to see if they are pulsing up and down or staying down like they should If pulsing trim one coil off of the spring at a time until they stay down

PREDATOR CARBS

Don't know about removing the springs but it sounds to me like as the blower heats up you losing pressure so the signal to the carbs is changing. I would play with the springs in the metering rods when the engine is hot, this is something you can do on the side of the road. I would go for a heavier spring. Edelbrock recommends the orange at 5".

Quote:

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Two model #1405 carburetors should be used on engines with positive displacement superchargers, such as GMC 6-71 blowers or equivalent. The following calibration changes make an
excellent starting point: Primary Jets - .101" (#1429); Secondary Jets - .101" (#1429); Metering Rods - .070" x .042" (#1450); Step-up Piston Springs - 5" (orange, stock); Needle & Seat
assemblies - .110" (#1466). This calibration has been tested on engines ranging in size from 350 c.i.d. Chevys to 440 c.i.d. Chryslers with good results.

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any pics?

i ran 2 750 eddy's on my blown 383 worked great. only problem was at the end of the 1/4 at 130mph it blows fuel all over the windsheild. i think if you read it says those carbs are not designed to be outside of the hood.
my buddy has eddys on his 440 and it works

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John, I have not seen any vacume at WOT on the engines I've dyno tested between the carbs and the blower rotors , same thing below the blower when at part throttle going to full throttle before boost is made It would (vacume signal)read vacume at part throttle in the blower intake and then go to zero and then start making boost This was with two 650 Holleys, two 1050 Dominators and two 750 carters, I have not dyno tested a roots blown motor with a single carb so I don't know if they wll make vacume under the carb at the upper RPM or not

Anecdotal experience varies, my 15% overdriven 6-71 would pull enough vacuum to close 6.5 power valves on a pair of 780 Holleys...Carter/Edelbrock works on the same principle.

From the Holley tech page:

"QUESTION What is a Manifold Referenced Power Valve?

ANSWER Nothing will kill a blower or Nitrous engine quicker that a lean condition. You want plenty of fuel available for the engine to use. There is a thing you need to know about the power valves on a roots style blower engine. The power valve is installed to keep the engine from loading up and running rich at an idle. On a normally aspirated engine the engine vacuum at idle will hold the power valve closed. When you step on the gas the throttle plates open and the engine vacuum drops as you accelerate. When the vacuum drops below the rating of the power valve , it snaps open and richens up the main system. On a blower with the carb mounted above the rotors there is constant vacuum all the time even under wide open throttle. The power valve will never open and you will have a lean condition. To remedy this there is a modification you can have done that is called manifold referencing the power valve. You plug the vacuum feed hole in the baseplate for the power valve. Then you drill a hole in the side of the main body into the hollowed out vacuum chamber for the power valve. You then insert a vacuum nipple in this hole. You will run a vacuum line to the lower intake manifold from the new vacuum nipple. Now you will have vacuum on the power valve at an idle, and when you hit the gas as the boost builds, it will force the power valve to open and richen up the main system. This can be done by most carb modifiers or even yourself. We offer quite a few different size blower carbs with this already done. Consult you local Holley dealer or our Techline for the correct application.
"

I had a pair of 750 Mighty Demon boost referenced carbs on mine until I went with EFI. They worked great, motor was 440 with a 8-71. I had a pair of edelbrocks on there before that and they were always a touch lean under full boost.

Matter of fact just reminded me I have to get rid of them