Quadrajet Problem Solving > Dialing in your rebuilt Quadrajet carburetor
17056228 First Test
blazer74:
Hello, Made some upgrades, Vortec 64cc head\intake setup from scoggins. Changed cam to Comps 268HE 218/454/110. Made a large difference in performance. Puts me just under 9:1 comp with pistons .040 in the hole.
Quadrajet 17056228 minor changes.
Basic Recipe 1
72/44cliffs
Idle tubes .035
Icr .047
Upper Mains .070 bushed
upper idle bleeds .069
Lower idle bleeds .076
Bypass air .086
Acc pump .026
Poe Disch .052
Air valve 3/4 turn/ with small notches in upper 2ndary blades
Adp 4.5
Mix 4.5
1.5" Edl wood spacer
Runs great except for hot start issue. Fuel seeping out of primary venturi nozzles and air bleeds after shut down requiring WOT to start after about 10 min. Seems like fuel is rising in bowl after shutdown.
Need to check a few things Cliff recomended. Fuel pressure, Inlet side leak. Well plugs.
Will get back with results. Thanks Craig.
1974 K5 Blazer 355 sbc
Vortec setup
Comp 268HE
Headers, dual 2 1/4 exhaust
35's 4:10 gears
blazer74:
Checked fuel pressure at inlet to carb. Found to be between 7-8 psi while running.
After shut down with fully warmed engine fuel pressure holds steady and then slowly rises after
aprox 10 minutes 9 psi, 15 minutes 9.5, 20 min 10 psi, using inline gauge non liquid filled. Heat soak at gauge could be a factor.
Restart fuel pressure goes back to 7-8 psi. After sitting 2 hours starts fine.
After approx ten minutes can see fuel in upper main bleeds and venturi nozzles.
Starts rough after about 5-10 min and hard to start after about 10-15 minutes.
Stock fuel pump typical 70987 2 lines.
Seems about right or just a little high for fuel pressure running.
Thanks Craig
Cliff Ruggles:
7-8 psi is fine for later carburetors. As long as the gauge holds pressure hot, it shouldn't be flooding, and how much fuel can be in the line after shut down under pressure that would make it's way into the carb and flood the engine. One would think if the pressure built up, and pushed the needle off the seat, the pressure would go down quickly?....Cliff
blazer74:
Changed the fuel pump to edelbrock street pump. Puts out 5-6 psi. I don't have the hot start problem with this fuel pump. Pressure also drops off also after a few minutes of shut down. Seems the stock pump was holding pressure after shut down and was increasing with heat soak in the lines upward of 10psi. I also bypassed the stock metal fuel line on the block.
I think fuel was creeping past needle just enough to cause fuel to raise in carb just enough to allow fuel to drip and not showing on gauge do to heat soak, sounds good anyway.
It still does idle very low when started warm until given just a little throttle, but starts easy.
Going to go back thru the carb and install bottom plugs, replace and vac test needle/seat etc.
Going to open idle tube from .035 to .036 as per stage 1 of Cliffs book.
(Do you think .086 bypass air is a little too much or ok for a 268adv 218@50 cam?)
Thanks; Craig
Cliff Ruggles:
Should be fine....Cliff
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