There seemed to be no end to the problems I was having with the idle mixture adjustment on both new and old carburetors in my M-series. The symptoms were: Idle mixture needed to be repeatedly adjusted. Idle rpm would suddenly drop, almost stalling. Engine seemed to run rich, even though mixture had just been adjusted correctly. Looking down the carburetor barrels I could see fuel trickling down above the throttle plates in one of the DCNF carbs. Repeated adjustments of the float levels did not solve it. Changing the needle valves did not solve it. I assumed (incorrectly) that the stock carburetors had not been correctly rebuilt and installed the new 44 IDF carbs. Initially everything seemed OK but soon the same symptoms appeared - except 10 times worse! Fuel was now trickling down from the accelerator pump jets on two of the three carbs during idle. Continued to trickle down for 10 or 20 seconds after the engine was shut down, depositing half an inch of gasoline on top of the throttle plates! Had to siphon the gasoline out from the barrels with a hose. This was getting serious, so I decided to temporarily go back to stock DCNF carbs and solve the underlying problems first. Long story short: It was all caused by excessive fuel pressure. Found to be 5 psi going into the carbs. Too much. Workshop manual says regulator is preset to 0.25 bar (3.63 psi) Turning out the adjustment screw all the way on the FISPA regulator/filter only brought it down to 4.5 psi. (The original FISPA FRB 11 only has an approx. 1 psi adjustment range) Leaving the pumps running for longer times, pressure slowly crept up to 6 psi. Way too much. 1. Found the FISPA FRB 11 fuel pressure regulator needing rebuild. Membrane old and stiff, probably a small pinhole leak somewhere. 2. Also found the fuel pumps installed were Facet Red Tops. Not ideal for the Dino, producing up to 7 or 8 psi. Should have been Silver Tops, with max 4.5 to 5.5 psi. Those two factors combined caused all the grief. The high fuel pressure simply overpowered the carburetor needle valves and gradually pushed up the fuel levels in the float chambers. The longer I had the engine idling, the richer the mixture became. No wonder it was driving me crazy. Temporary fix was to install a Malpassi fuel regulator at the inlet to the carburetors. They are adjustable over a wide range and work very well. I set it to a very low 2.9 psi (0.2 bar) to be on the safe side. The idle now became steady. No more flooding issues. Image Unavailable, Please Login Permanent fix: Out with the old, bye-bye to the Facet Red Tops. Will not be missed. Lovely original FISPA FRB 11 will be restored and saved for the future. Image Unavailable, Please Login In with the new: New Bendix look-alike pumps with correct pressure rating. New Malpassi Filter King pressure regulator/filter. Not exactly like the FISPA but close enough for now. Image Unavailable, Please Login At first I planned to just put the pumps in parallel to duplicate the original look and function. But I like the idea of having one pump as a backup to the other, and to be able to run either one pump or both. To make that possible, I had to install a one-way valve in the output line of each pump. It is only a minor deviation from the original setup, and easily reversible. Searching this forum, I found that Adrian (alhbln) had already done a similar setup, except for a different reason (vapor lock) and with Pierburg pumps. Details here: https://www.ferrarichat.com/forum/threads/new-fuel-pump-setup.372894/ Later I plan to install two hidden toggle switches controlling the pumps under the driver's seat, for example. Here is the setup installed in the car. Image Unavailable, Please Login I set the pressure set to a conservative 3.0 psi (0.21 bar). Now it always stays at that value, engine running or not. Recent warm and dry weather last week enabled me to take the car for a three hour drive. It drove very well and the idle was always steady and healthy sounding. So far, so good. In conclusion, the issue of fuel pressure is rarely discussed here, but my experience tells me that it is quite critical in the Dino, and is becoming more critical as components are aging and original parts are replaced with aftermarket items. Currently available needle valves for example, seem to vary quite a bit in their ability to hold off fuel pressure. Even the factory preset value of 0.25 bar (3.63 psi) seems borderline too high now. Experienced carburetor people seem to agree on a range of 3.0 to 3.5 psi (0.21 to 0.24 bar) as ideal for the Weber carburetors, and no more than that. Fuel pressure is easy to check and well worth keeping an eye on.