General Category > Quadrajet Carb Talk and Tips
1973 800 CFM Mods
Grych:
Nice work on that quadrajet! I always like those 70 GS models. 540 C.I. stock appearing. Hows does Cliff say, rip your head off and throw it in the backseat!
Anyway, I myself had wondered if an adequate vacuum signal would remain at the main if the casting ring were removed in addition to the outer booster ring. One would think a fairly high velocity would be required to create the pressure differential for enough fuel flow. IMO, main air bleeds would need to be reduced. Have you played with the main air bleed sizes?
Would you post the other primary settings? Idles tubes, channel restriction, especially main and lower air bleeds.
Cat
Grych:
What were your Air Fuel Readings at the 127 MPH mark?
Cat
Jim Rodgers:
Grych,
This carb was originally a basic stocker build by Hedworth. The carb was dead lean from the get go. All of the additional mods were done by me including the porting, removing the casting and booster rings, modifying the air horn etc. I have upped the primary jet size significantly and removed the primary metering rods, went to a smaller float and a needle seat with the windows. It is still lean but not head gasket killer lean.
I have not touched the main air bleeds, idle tubes, channel restriction or main/lower air bleeds since I got the carb from Val, hence the reason for my post. I'm looking for advice and tips on these areas. Also want to know how anyone has gotten larger than a .149 needle and seat in these things. I'm a fairly creative person, but havent figured that one out yet. I want in the neighborhood of a .175. I'm not looking for anyone to divulge any top trade secrets on a public forum so please dont take me the wrong way. Just looking for tips from anyone who has been there and done that.
Cliff Ruggles:
Considering 88 primary jets and the smallest rear metering rods you could fine, I'm still thinking that something is fundamentally wrong someplace.
I've removed the booster rings from the early large cfm Buick castings many times, and set them up to run straight off the jets.
Jet size usually ends up around .070-.073" with no metering rods, with the secondary rods in the .040-.055" range.
It's possible the fuel bowl isn't staying full on hard runs, or there is simply too much emulsion air, or both.
Most racers run smaller seats and more fuel pressure these days, but we have successfully managed a .160" seat in those carbs at 7 psi fuel pressure..... Cliff
Jim Rodgers:
Cliff,
Sent you a PM when you have the time. Thanks,
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