hello to all
I will first say that I do not have a Cobra or GT40. But I am hoping some here may be able to shed some light on this issue, as I have been fighting it for a good 9 years plus, and seem to be "on my own" in the small circle of guys with similar engine/modifications.
So here we go. The engine is an air cooled Volkswagen type 1, 2165cc, running 91 octane, two Weber 48IDA, 40mm venturis, 60F10 x 115 air holders, F4 tubes, 165 main, 180 air, closed pump jet. Fuel pressure is 3.00psi metered by Malpassi Filter King regulator. Carburetors are mounted about seven inches above intake flange on head on cast aluminum manifolds. I have ~4mm thick fiber gaskets between Webers and manifolds. If we need to discuss other specifics in the engine, I'd be happy to.
The floats are set to 5.5mm above carb body/24.2mm drop to needle-valve tongue. Needle valves are 2.00.
The issue that came up about 9 years ago- out of nowhere I might add, is that after running the car sufficiently to warm intakes and get
oil to 150-170F or higher, if I shut the car off and walk away for 15 min or so, once I go to restart it and set off, it runs as if the mixture screws are closed or that somebody swapped 50 idle jets in for my 60's. It will barely idle, and if I immediately drive off, it will buck and nosedive until I feel it pick up main circuit, at which point it will come on. After 15 minutes of normal driving, this goes away and the car will run strong again. It acts as if the float levels are much too low (when I first started setting 48's up on VW's in the early 1990's I learned through my mistakes what too low float levels cause).
An AFX AFR sensor is confirming it is very very lean when this happens. Asthe car struggles to idle, I am seeing 15.00+, and when throttle is crept open, it will spike 16.00.
I have read a lot about Weber fuel boiling here and on some of the Mazda RX7 and Porsche sites. It seems the common issue is the fuel will boil over during heat soak and dribble through nozzle in aux. venturi, (or acclerator pump nozzles) into intake throat, flooding the engine. I don't think, based on lean symptoms, I am experiencing this. But maybe I am so frustrated I am being blinded and not seeing the big picture. Again, no help from the VW world. Some have said they do not drive their cars as much as I do so they are not experiencing it. From what I have read here, it seems many of you have a better grasp on the Weber 48IDA, the fuel boil issue and remedying it.
Again, I am sorry for bringing in a problem from a non-Cobra/GT40 world, I I understand if this post is inappropriate.
I'm just looking for some help
Thanks and happy hoildays