Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem
How to Measure Inlet Pressure Capability?
Shiny:
I got this done.
I poured gas in the carb, filled a tube, and pressured with air using a low-pressure regulator.
I cranked it up while holding the float pin.
The needle and seat held fine until I hit 12 psi, at which point it was obviously "overwhelmed".
FYI, I measured the seat ID at 0.128"... likely way more than I will ever need.
The good news is I can eliminate overpowering the needle and seat as a cause for flooding as long as my pump pressure is close to what it should be.
Rather than guess on cleanliness and performance of my pump, I bought a new Delphi brand.
Onward.
ourkid2000:
Shiny what fittings are you using there to test that inlet? I'd like to pick up something similar.
Shiny:
I bought a low-pressure regulator off Amazon. I always try to find stuff local but I struck out on this, at least for a reasonable price.
https://smile.amazon.com/dp/B01BPQDG62?ref=ppx_yo2ov_dt_b_product_details&th=1
The only tricky fitting was a 3/8" male flare to 3/8" barb adapter for the carb inlet. I found it on the rack at O'Reilly's.
This might be it.... double check, though...
https://www.oreillyauto.com/detail/c/dorman/dorman-fuel-hose-fitting/dor0/785402d?q=dorman+fuel+hose+fitting&pos=4
Here's another style that might work. Again, double check...
https://www.oreillyauto.com/detail/c/american-grease-stick/american-grease-stick-3-8-inch-90-degree-clamp-elbow/ags0/chf28b?q=3%2F8+male+flare+to+3%2F8+barb&pos=4
The other fittings for the regulator were common 1/4" NPT fittings I had laying around: one 3/8" barb and one male quick-connect for my air line. I set the pressure on my compressor to 20 psi and fed it to the low-pressure regulator.
I filled the carb body and tube with gas, then plugged it onto the regulator. To keep gas out of the regulator, I had to have the tube and the regulator above the carb which was a little awkward. I had a big plastic tub under it all to catch the spills. It took all of about 2 minutes to measure the spill-over pressure... so a lot of cost and effort to get this done but I was tired of wondering.
Speaking of fittings, does anyone know of an easy way to measure the fuel pressure at the carb inlet? Would be nice to find a tee made for this that had a male flare to the carb, a female flare to the hard line, and a tee to a barb for the pressure gauge. The hard line between carb and pump makes it a pain to hook up a gauge.
Mike
ourkid2000:
Thanks so much for this information. I think you provided everything I need!
bry593:
--- Quote from: Shiny on January 25, 2023, 12:34:00 PM ---I got this done.
I poured gas in the carb, filled a tube, and pressured with air using a low-pressure regulator.
I cranked it up while holding the float pin.
The needle and seat held fine until I hit 12 psi, at which point it was obviously "overwhelmed".
FYI, I measured the seat ID at 0.128"... likely way more than I will ever need.
The good news is I can eliminate overpowering the needle and seat as a cause for flooding as long as my pump pressure is close to what it should be.
Rather than guess on cleanliness and performance of my pump, I bought a new Delphi brand.
Onward.
--- End quote ---
Nice work. That's similar to my method, but I just turn my devilbiss regulator down to 5 psi and blow through the fuel inlet with a standard rubber tip blow gun.
A lot of the aftermarket mechanical fuel pumps will spike much higher than 7 psi. The fuel regulator is a great way to address this issue.
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