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After reading all the how to on the forum(thank you guys for all the effort and time to explain) i decided to try it doing my own carb. I started by porting a 79 manifold making the channels and plugging all the extra ports. Then hogging the primary venturies and cleaning the boosters. I still need to more work but i think is comming along nice. I just have to figure out what am going to do with jets sizing.
Last edited by chiquito1228; Jan 10, 2019 at 12:03 PM.
You need to redo those venturis. The narrowest part needs to be at the hole Mazda used for pulling a vacuum to activate the vac secondaries. Larger venturis change the calibration of this circuit so you must now set yourself up for mechanical secondaries. And if you can, you must change the point at which they open according to primary throttle position. Stock is about 50% of primary opening but I like opening them closer to 75% throttle position. If that doesn't make sense, don't worry about it.
Make the upper edge as thin as humanly possible. This is where the air comes it at, so it makes sense, right? I like to go for as sharp as a box cutter blade, but I've been at this for a while. Your mileage may vary. In other words, be very careful.
Oh and avoid making any sort of smoothed rounded bellmouth shape anywhere on these. That will hurt you. It must be sharp at the upper edge and sharp at the "choke point" (the narrowest part where it "chokes" down at the hole). If you keep it sharp, it produces a stronger vacuum here, which is what is required for the boosters to work properly. You will notice the bottom of the booster is in line with the hole. Do not make a bellmouth shape here because that allows the air to slip in too easily like a velocity stack. Not a good idea where a vacuum is required to do "work" aka to pull fuel out of a booster and on into the engine.
The bottom of the arms on your boosters appears to be stock (square, dull shape). You might want to consider filing them to a nice sharp pointed edge like an airplane wing. Go slow and use finesse. Like an upside down teardrop shape. I call it an aerofoil shape but that might not be proper terminology. Thoughts?
That's pretty good. I like to aim for about a .05mm variance in roundness, and try to get them to the same ID within about .01mm but a slight variance like what you have is probably ok.
