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post #9 of (permalink) Old 08-19-2018, 11:21 AM
Gordon Raymond
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You need a regulator AT THE WEBERS to adjust pressure. Webers may need high flow rates for racing with modified 2L's but pressure is not helpful. Particularly with brass float Webers. The floats weigh 26 grams, and with needles and seats of 2.0 or larger, it is possible for pressure to overwhelm float weight causing flooding. Later design Webers that used plastic floats have different float hanger geometry, and will tolerate a bit more pressure. How much? I don't know as I've never checked.
However, the regulator serves 2 or 3 purposes. Most have a built in filter. The diaphragm absorbs a bit of the fuel pulses from most types of fuel pumps, reducing wear to the float "paddle" from the needle. The third purpose is to be sure pressure is low enough not to overwhelm floats, yet volume high enough to keep the fuel level in the bowls constant.
Suggested pressure for Webers with up to 2.0 N & S is 3# running. This is for brass float designs, and is fine for plastic floats as well. The low pressure will depend somewhat on engine use, the intent to keep fuel level in the bowls from dropping with constant high rpm use.
From my personal experience with Webers over many years.

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