Quadrajet!!!

[TheSaint]

Hello! Some of you guys helped me out with a quadrajet issue. Well I got another. After fixing choke and fuel line issue, I got another. When I start car it idles decently then all the sudden it hisses, spits gas out the primary area then turns off! Any suggestions?

 

[rfpowerdude]

Primary float has a hole in it and won't close the needle feed. In other words, sinks and gas keeps flowing until the primary overflows into the intake and floods the engine.
Replace it.

 

[TheSaint]

Primary float has a hole in it and won't close the needle feed. In other words, sinks and gas keeps flowing until the primary overflows into the intake and floods the engine.
Replace it.

Is it basically just flooding?

 

[rfpowerdude]

Is it basically just flooding?

Yes, at idle, the engine doesn't need much gas and the fuel pump fills up the bowl. The needle valve/seat that is controlled by the primary float floating to the top and closing it (mostly) to keep the fuel level constant. If the float either gets a hole in it (or the nitrile version has an issue) and stays at the bottom, the fuel pump flow is not controlled anymore and overflows out of the primary flooding the engine.

Once you get it open, you can check to make sure the needle valve is still in place. It might have come loose. If it is still intact, you can take the float out and put it into a container of gas and see if it sinks.

Whatever the actual cause is, it is a pretty common symptom of the primary float/needle valve.

 

[TheSaint]

Yes, at idle, the engine doesn't need much gas and the fuel pump fills up the bowl. The needle valve/seat that is controlled by the primary float floating to the top and closing it (mostly) to keep the fuel level constant. If the float either gets a hole in it (or the nitrile version has an issue) and stays at the bottom, the fuel pump flow is not controlled anymore and overflows out of the primary flooding the engine.

Once you get it open, you can check to make sure the needle valve is still in place. It might have come loose. If it is still intact, you can take the float out and put it into a container of gas and see if it sinks.

Whatever the actual cause is, it is a pretty common symptom of the primary float/needle valve.

Thank you for the rundown I really appreciate it. I’ll tear it down and see what I can find. Much appreciated!

 

[CopperNick]

Nope. Flooding is a state of affairs that occurs when you whack the throttle pedal too many times while trying to do a first start in the morning or after sitting a while and too much gas gets down into the cylinders so the plugs get wet and won't fire.

What you have is exactly how rfpowerdude described it. When you lift the top of the carb off and take a look at the float, or, once you have the lid off you gently shake the float, you will either find evidence of damage, like the pinhole mentioned, or you will hear the sound of liquid sloshing around when you shake the float.

The older brass floats are notorious for developing leaks simply because the new formula gases that now get pumped into our rides are actually caustic to some extent and the chemicals in them will soften and destroy the lead in the solder that was used to assemble the two halves of the float together. Even if the float is not brass, it can become porous and absorb fuel; that makes it heavier than it ought to be and therefore prone to sink. Once it has sunk, the spring on the float pivot pin is not strong enough to bring it back up which means the float needle will fail to reseat itself and fuel just keeps pouring into the bowl. it has to go somewhere so the hissing is the fuel attempting to escape via the air bleeds and the bowl vent. No fuel, no go Joe.

The cure is basically to remove the dead float and replace it with a new, good one. Be sure when you do so to level the float according to the measurement provided in the kit so that the correct amount of gas will enter the bowl; tool little and you starve, too much and you flood.



Nick

 

[rfpowerdude]

No problem! When you take off the air horn, you will see the float that is on a pivot. As the float goes all of the way up as the bowl fills, the opposite side of the pivot from the float pushes the needle down into inlet closing it off. You'll see how it works when you get it opened up.

EDIT: Nick posted while I was typing and I was not paying attention

 

[Bonnewagon]

There are various reasons for flooding, some as posted above. Bad leaking float, wrong float setting, too much fuel pressure, poor seating of float needle, and my favorite- return line plugged. If you have a three port fuel pump, one port is fuel inlet from tank, one is fuel output to carb, and the third is return line to tank. That type pump is usually used on AC equipped cars to prevent vapor lock. If you delete the return line for whatever reason, then just plug the port, the pump sends all of the fuel to the carb. That overwhelms the float and you get flooding. Sometimes it is just a crummy idle with fouling plugs, and sometimes it is drastic flooding like the OP complained about. The correct method is to use a 'T' fitting that runs the return fuel back to the input line. I think the sizes are 3/8" for the tank input hose that jumps from frame to pump, and 1/4" for the return line hose. This can also happen when your car has no return line, but all you could find was a three port pump. You plug the return line and get problems.

 

[Bonnewagon]

PS: Nick, I replaced all my Q-jet floats with brass floats. That ended all my sinking float problems. It took some searching to find a supply, but I bought a half dozen for each of the three series of float bowls that Rochester used over the years......................................................................................................................

 

[CopperNick]

Not surprised. That bit about the factory float becoming porous, or a fuel sponge if you prefer was almost epidemic to Q-bogs that had been sitting for a long time or which had been harvested from pick a part yards or kept when a project was offed and then shelved "Just in case" Not real sure what the factory used for its floats but the stuff apparently had a bad habit of decomposing over time. Causes I have come across have included U-V damage, chemical damage from gas additives, and a few others.

When I ran my Hollies, I swore by the brass floats as being superior to the nitrophyll ones, until I ran into that same problem with a sinking float. You could actually hear the fuel sloshing around when you took the float and shook it. Got into a discussion about it with my local indie speed shop owner and he noted that as the gas companies changed the formulae for the pump gas they offered what had begun to happen was that the gas started to "eat" at the older floats. The consequence was that the lead with which the solder in them had been formulated was being leached out and that caused the floats to become fragile and the seams to pop open and allow fuel to get inside them.

The newer brass floats apparently do not have this problem because they switched the solder being used to one that has no lead in it. However, by that time I had switched to the new nitro floats, (or whatever the generic name for what they are made of is) and then benched the Hollies permanently; mostly because they had an insurmountable issue with humidity and cold weather starting that I never could dial out of them.

I have learned over time that that is the principal complaint of many Holley owners when they go bench racing; Effectively it is the ongoing need to repeatedly retune the carb almost daily or even more than once per day to get it to play nice if there is a change in the weather, hot/humid seems to be the worst culprit. Which is too bad because, at speed on the interstate, the Holley performed famously. Need to pass? Drop on the Waa-Was pedal and listen to the Hooomph of the secondaries coming on line and watch the look of shock on the other driver's face as you move on by and get on down the road. Only thing was that if you moved from the lowlands to the Black Hills, you guessed it, time to tweak the idle mixture, again.

In a car, it is easy to get to the carb and tweak AFR or idle mixture; for the van it requires that a large amount of the dash be disassembled. And while it is fun to drive around and listen to the roar of air being sucked into the engine, and listening to all the various sounds and noises, it is not safe, but then, a lot of what we tend to consider as being fun, isn't, safe that is.................

Anyone for a couple of beers and a rope swing out over the lake?



Nick