Cliff's Quadrajet Parts and Rebuild Kits

Quadrajet Problem Solving => Diagnose a Quadrajet carburetor problem => Topic started by: baxternick on October 13, 2016, 11:35:05 AM

Title: Needle & Seat selection
Post by: baxternick on October 13, 2016, 11:35:05 AM

I have posted about leaning out when near my peak rpm.  It is definitely a fuel starvation issue.  I currently have a built cadillac 500 with some mild head work, intake, mild cam, robbmmc pump, 8 an fuel line, 1/2" pickup in tank,  and a quadrajet that runs perfectly otherwise.  The fuel pressure stays strong @ 5-5.5 lbs during a hard pull at peak.  The carb has 77 jets,  53m rods, L hanger, and CE rods.  I even tried AX rods and it still leans out.  The carb has the 135 needle seat now.  Should i be running a 145 neele seat because of the thirsty Cadillac big block? Does the larger seat change any other settings in the carb?

Title: Re: Needle & Seat selection
Post by: 77cruiser on October 13, 2016, 01:00:39 PM

I'm in the same situation I'm running a .140 seat & by the AFR it's leaning out about 5800 & spikes at the shift then comes back.The only thing I think you'd have too do is lower the float setting a bit to keep the fuel level the same.
I posted my situation in carb talk & tips to see if I could get some more feedback.
How much HP are you putting out, do you know? Mine is around 530 hp.

Title: Re: Needle & Seat selection
Post by: baxternick on October 13, 2016, 01:33:33 PM

I have no clue about HP numbers. The Cadillac big blocks stock numbers are a little high to me.  With the head work, higher compression, intake, cam, and rocker upgrades I would be happy if I had 400ish. This is my first V8 other than my yukons 5.3, so I have no way to gauge it.  If is scary fast,  and the torque is amazing. It may be way higher but I have zero idea about what a typical big block puts out.  Guess I will give the. 145 seat a shot.

Title: Re: Needle & Seat selection
Post by: Cliff Ruggles on October 14, 2016, 03:38:50 AM

For 500 cid or over 500hp nothing wrong with running a larger N/S assembly.  I run a .145" seat in my carb, engine makes around 550hp.  I'd also run a bit more pressure unless you are using an early Caddy carb with the early float and hinge pin location.

We sell N/S assemblies in .140, .145, and .149" and they can be ordered directly off the website, just state the size desired where it asks for the carburetor part number........Cliff