Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem

17059216 new issues vs old issues

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olnick:
Hello all: I completed the second recipe on the carb.
Original: was a bear to get started cold, Ran okay after it was HOT. got 18-20 MPG idle needles did next to nothing ran with them 8 turns dr 10 turns psg side. secondaries were working!
with changes:
idle tube .036
idle down ch. .048
up air bleed   .067
lower air bleed .070
idle by pass air .050X2=.100
Holes under idle mix screws .098
main air bleed .070
Needle seat .125
Main air bleed horn .070
MJ       71
rods   41K
hanger  K
sec rods  CH
spring 3/4 turn
pull off  2 sec.
sec flaps 1.308
APT .047 down 1 1/2 turns in from flush

starts right up from cold if not sitting more than 2 days!  if more than two days need to crank to get fuel into bowl.
runs great from cold through HOT       MPG 12-14 on a good day!!
By pass air was not correct: I was able to use a different PCV valve to fine tune the bypass air.
Idle needles: Will stall if both turned all the way in. After 1 1/2-2 turns out NO difference psg side 1 1/2 dr side 2 turns out. I can unscrew them all the way without taking them out it continues to run.
17-18 in vacuum.
I have a Rhodes cam and lifters installed
CAM HAS 211 DEGREES AT .O50

Frank400:
Hello olnick and welcome to the forum.  I don't claim to be an expert but if you don't mind, I have a few comments regarding your build.  The carb you built is the kind that I prefer.  I've built quite a few of them and in fact, I'm actually building one right now.  Here are my comments/interrogations on your build.

   The idle air bypass is already .070" on each side on this carb number, what was yours before and after, as I'm not sure I understand your .050 x 2.   


    Also, 1.5 to 2 turns out is next to nothing with those metric threads.  I can see you increased the size of the idle tube but not the idle down channel restriction ?

    CH rods is kind of lean on the secondary side. 

  I can see that you reduced the size of the main air bleeds, both upper and lower, as those are usually .120" on those carbs.  Did you use the small brass inserts that Cliff sells ?  They work great for that. 

  Did you try playing with your APT position ?  Usually quite a few MPGs there if you're off.

  what is the car/engine combo ?

Cliff Ruggles:
What are the engine specs?

olnick:
Thank you Frank400!  I re read my notes:
The idle air for each side measure .o5o in.  Dr side .050 + psg Side .050 =.10 total
The idle down ch went from .048 to .052 my error from notes
MJ 71 to 73 again  my error my notes!
I do have a draw full of secondary needles. recommend??
Yes I did have the little brass caps, they work great to re-size the bypass holes!
I have NOT tried to adj the APT yet.
SBC 355cid. "heavy" cast heads 1.94 In. 1.50 Ex. 9.5:1 CR with flat top pistons. 12 deg initial adv. 36 deg total max adv mech. ported vacuum 10 deg max.
Rhodes cam and lifters installed  10W/30 full syn oil
THE CAM HAS 211 DEGREES AT .O50

Cliff Ruggles:
What are the casting numbers on the heads?

What are the rest of the cam specs, grind number, who made it?

Big difference in idle and off idle fuel requirements for a "211 @ .050" cam if on is ground on a 107LSA and another on a 114LSA.

Head castings numbers tell me chamber size and flow characteristics (power potential).......Cliff

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