I have a sbc 350 with a quadrajet 4 barrel in my PU. If it sits a couple days I have to crank for a long time for it to start. I have heard that the quadrajets can leak through the plugs in the bottom of the bowl. Mine looked good but I JB welded them anyway and rebuilt the carb. Still the same. I added an electric fuel pump that I run for awhile (long while) before starting. That helps. It appears that I'm loosing fuel while parked? Is this a problem with the quadrajet or something else? Anyone else have this problem? No sign of leaking around the carb or fuel lines. HELP
It's the modern fuel, has a low boiling point and evaporates quickly. Is your electric pump mounted near the tank and at least even with the bottom of it?
I don't think it's the fuel. I also have a falcon with a SBF that I use the same fuel in. It can sit for a couple of weeks and fire right up. I'm running a holly 4brl on it. My SBC does have intake manifold heat operated choke. How do you block the exhaust cross over? Do you have to pull the manifold and block the ports? If I block the exhaust cross over to I need to change to an electric choke?
I had an oldsmobile that did that. I put a Holley on it. You can get electric chokes and I udes to sell manual choke conversions for the Q-jet back in the day. Maybe JC Whitney has them. Quadrajets are good carbs. A guy told me to check that there's no leaks in the fuel lines, that the gas may be siphoning back through a pinhole somewhere. I never got that far. I blew the motor up on the test run after putting the Holley on it.
Some people will tell you that JB weld will not hold up to gasoline, my experience has been otherwise, I patched a hole in the bottom of a gas tank 15 yrs. ago with it and it is still holding. Is your choke working good, do you have a good healthy squirt from the accelerator pump when looking down into the carb?
Your pump should only need 10 to 15 seconds to fill the bowl, at the longest time. Look for some kind of leak, air or fuel.
The early (1965~1967) Q-Jets (early 1968 on a very few models) did leak through the well plugs. This was corrected at the latest by mid-1968. It is probably the fuel. Different carbs have different issues with the fuel. Holleys have the bowls off to the side with an air insulation between the bowl and the engine. The Q-Jet has the bowl directly above the throttle body. Just to prove this to myself, I once removed one of the tops from one of the AFB's on my 390 about 30 minutes after shutdown. Bowl bowls were bone-dry. If you are un-familiar with the AFB design, there is no hole in the bottom of the bowls for leakage. The fuel evaporates out of the vents. An electric pump solves the issue. Jon.
Carbking, Do you run the electric with the mechanical or eliminate the mechanical? Do you recomend blocking the exhaust cross over also? Would a thick alu spacer between the carb and carb also help?
I have seen the electric pump run with and without the mechanical pump; however, some electric pumps will NOT function in this manner. Blocking the cross-over is a racers trick that will improve WOT power by maybe 1 ~ 1.5 percent. Some with showcars do it to prevent paint burn-off on the manifold crossover. IT ADVERSELY EFFECTS DRIVEABILITY!!! If I had a dollar for every prospective new customer that has called in the last 15 years with major driveability issues for the first 30 minutes, especially with an auto trans; I could buy Hawaii and retire. And yes, about 15 years ago, I listened to those who gushed about the power increase, and did this to my own car. Even with a manual transmission, it was a handful to drive for the first 30 minutes. I finally installed a manual choke to force-feed extra enrichment until everything warmed up. An aluminum spacer will probably not help. A fiber spacer might. Aluminum conducts heat too well for the aluminum spacer to stop the problem. Jon.
I had this happen in an O/T car. It was the fuel pump. Sounds like you have one of the two valves going off in the pump. Cosmo P.S. I, too, didn't think this could be it. However, it was all I changed, and it fixed it.
The fuel trapped in the line gets hotter as the engine is shut off. As it gets hotter, the line pressure goes up and sometimes forces fuel past the carburetor's needle and seats
The cure is to install a fuel filter (inline say a Fram or?) with three lines, where one, through its tiny restrictor, goes back to the fuel tank. This prevents the carb from over filling and dripping into the manifold. You might have this prob along carburetor percolation, and be needing one of those GM or Mr Gasket aluminum plates and a stack of carb gaskets. Those plates prevent both radiant heat transfer AND conducted heat transfer. The stack of gaskets can compress while tightening and break an ear off a Holley, so be careful with Holleys. The GM plates had a hard insert to prevent breaking Holley ears.
This is one thing that you need. http://pitstopusa.com/i-22956262-mr...uretor-spacer-quadrajet-four-hole-design.html Another thing to have would be a fuel filter with a check valve. There should be one available to go in the carburetor. You say that the electric pump has to run for quite a while to get the carburetor full so the fuel has to be draining back. It shouldn't take more than a few seconds for the pump to fill the carb. You could also put one in the line. I like to use a filter with a return to tank so fuel is constantly flowing and stays a little cooler.
Same deal here= evaporating. What the king said about the bowl's is correct. Fuel isn't what it used to be either with different blends= summer/winter. Holley vehicles can sit for months, and fire right up. My Q=JET has to be started once every 2 weeks= bone dry. Pump(s) =plural, are fine...... Just a P.I.A at times. I'm so tempted to switch over for that reason, but Pop's truck, and it will stay that way....... I even have the air valve lazy..... I don't need things getting slideways in a blip of the pedal. Big difference between leaking(puddling), and evaporation. Yes- have a spacer. Just the nature of the beast..... But- when tuned correctly= Hold on!
The Jalopy Journal
