Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem

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crane_guy:
i have purchased a performance q-jet from jet performance and i am having nothing but troubles the number of the carb is 17057584. this carb is modified and advertised to work with a 400 hp small block. i have a fresh rebuilt 454 9:1 compression with a comp cams extreme 4x4  cam (idle to 5000 rpm) the motor makes  20 hgs of vacuum at idle if it means anything the elevation of where I live is 3700 ft
. the crab has 74 jets 41 metering rods da secondary rods and they set the float at 1/4 inch. i am  also using a large style mechanical fuel pump. The first problem I had was too much fuel pressure it was leaking out of the air horn gasket and flooding the engine bad enough that I ended up with fuel in my oil. the filter that came in the carb was open at one end with a cork gasket, when I installed a filter with the rubber end  that has a check valve, this helped my problem. But did not fix it. Now I have not yet installed a fuel pressure regulator but I am going to tomorrow, right now I am running the carb at the recommended 15/32 float hight (as per rebuild kit sheet specs). The manufacturer says that this carb will not work with a big block and I am not sure why? I also dont understand why they have blocked the idle bypass air by plugging the holes in the void beside the primaries in the main body ( the holes that you show on page 29 on the bottom right corner in your book) I do believe that the system is complete except for the epoxy plugged holes. If I were to remove that epoxy what gaskets do I need to make it work ? At present the truck idles smooth except for a surge lets say it occurs every 10 seconds at idle. It feels sluggish and bogs put at full throttle it just have that clean sound.

I am going to install the regulator and gage, what fuel pressure should I have ? What is ideal ?  Should just set it so it will work with a ¼ inch float hight? And what do you think I am going to need to do to make it work with my 454 and by the way this engine is in a 4x4. Any help would be appreciated love the book thanks !

Thad 

Cliff Ruggles:
Not sure where to start, all that I can say is that we get a LOT of carburetors in here built by other sources for custom calibration and performance mods, etc.....Cliff

crane_guy:
ok so  i drilled 3/32" holes in the primary throttle plates  raised the float to 5/16ths and she has a great idle no nozzle drip! i am not sure if its correct my mixture screw are about 4 turns out idling at about 900 rpm. i hate a moderate bog of idle, so i pulled the accelerator pump linkage, and that made things worse so i turned the apt screw out to three turns( was 2 turns out)A now i just had a slight hesitation hooked the accelerator pump back up and it runs not bad :)
i guess i should start by measuring all of the idle circuit ? is using drill bits a satisfactory way of doing this ?
 what are you thoughts on the fuel pressure fluctuations ?  plugged return line ??

Cliff Ruggles:
Any particular reason you didn't unplug the blocked off idle bypass air passages?  More effective than drilling small holes in the throttle plates, but if it helps that's a good thing.

I'm not familiar with that carburetor part number.  What size are the main airbleeds?....Cliff

crane_guy:
acctually i have 2 of these carbs from jet with the same q jet # the first one i used before the rebuild, it had a bit of an accident while the motor was being rebuilt i just simply drilled the throttle plates from the first one to use on the second one just as an experiment and it seems to have worked.  but really i do not know enough to remove the blockage i didn't want to solve one problem and create another. i still think i have a fuel pressure issue i dont like how i have a steady 5.5 psi at idle and then when i rev the engine the pressure drops to 3 and jumps up and down between 3 and 5  i am going to get a new fuel pump before i do any more tuning

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