Quadrajet Leaking Fuel From the Top of Accelerator Pump

[bigchip06]

I’ll start this thread off by saying I have minimal knowledge of carburetors, which is one of the main reasons I rebuilt my working carb to begin with; to fully understand them.

Now, after rebuilding my quadrajet with a kit from O’reilly’s, it’s leaking fuel from the hole for the accelerator pump rod immediately after startup, a pretty substantial amount too.

I’ve taken it apart a handful of times and made sure everything is correct and I’ve tried lowering my float level.

Is this as simple as a bad acc. pump gasket in my rebuild kit or could it be caused by something else?

 

[Matt69olds]

Get a accelerator pump kit from Cliffs Q-Jets, Jet Performance, or some other carb specialist. The last time I used a parts store rebuild kit they were absolutely garbage, I seriously doubt the quality has improved.

I bet you find the accelerator pump piston doesn’t fit the bore very well.

 

[SirRobyn0]

I agree with Matt, but also have a question, does it leak just sitting there at idle, or do you have to work the accelerator pump before it leaks?

 

[bigchip06]

Get a accelerator pump kit from Cliffs Q-Jets, Jet Performance, or some other carb specialist. The last time I used a parts store rebuild kit they were absolutely garbage, I seriously doubt the quality has improved.

I bet you find the accelerator pump piston doesn’t fit the bore very well.

That’s what I’m betting too, just wanted to get a second opinion before I spend money on a new kit. Thanks for the recommendations

 

[bigchip06]

I agree with Matt, but also have a question, does it leak just sitting there at idle, or do you have to work the accelerator pump before it leaks?

Yeah it’s instant, no throttle input and it’s already leaking. I also noticed if I simply pump the gas too much before starting it will leak without even running

 

[75gmck25]

It’s probably the fuel level that is too high and it’s venting around the pump rod. Another possibility is high fuel pump pressure overcoming the float needle.

 

[bigchip06]

It’s probably the fuel level that is too high and it’s venting around the pump rod. Another possibility is high fuel pump pressure overcoming the float needle.

I already tried lowering the float level to the same exact result and I didn’t change anything externally that would’ve increased the fuel pressure since it ran last. Unless it could change internally by the metering rods or whatnot?

 

[fast 99]

Caused by high fuel level. The accelerator pump well is filled from the float bowl.

 

[SirRobyn0]

@bigchip06

Ya you only have two maybe three possibilities.
#1. If it only leaked when operating the pump, then the pump could be at fault.
#2. Something causing high fuel level. If you are 100% sure the level is set correctly take it apart to be sure there isn't a piece of debris on the seat, a defect in the needle and seat or assembly issue. If you installed a new float maybe it's defective and not floating. You could always swap your old parts in just for a test.
#3. High fuel pressure over coming the needle and seat.

Like most of the other folks are saying #2 seems most likely, I'm sorry but there just isn't a lot of other options. You know if your concerned about an assembly issue you can take it apart and post pictures of how you have it set up and we'll tell you if everything looks normal to us or if one of us spots something.

 

[bigchip06]

@bigchip06

Ya you only have two maybe three possibilities.
#1. If it only leaked when operating the pump, then the pump could be at fault.
#2. Something causing high fuel level. If you are 100% sure the level is set correctly take it apart to be sure there isn't a piece of debris on the seat, a defect in the needle and seat or assembly issue. If you installed a new float maybe it's defective and not floating. You could always swap your old parts in just for a test.
#3. High fuel pressure over coming the needle and seat.

Like most of the other folks are saying #2 seems most likely, I'm sorry but there just isn't a lot of other options. You know if your concerned about an assembly issue you can take it apart and post pictures of how you have it set up and we'll tell you if everything looks normal to us or if one of us spots something.

Thanks for the response, I guess I could put my old needle and seat back in tonight and see if that makes a difference. My logic was that fuel shouldn’t be able to flow past the acc. pump gasket regardless but your explanation makes sense

 

[Bextreme04]

Thanks for the response, I guess I could put my old needle and seat back in tonight and see if that makes a difference. My logic was that fuel shouldn’t be able to flow past the acc. pump gasket regardless but your explanation makes sense

The acc. pump seal is only in the bore and shoves fuel towards the pump shot nozzle. The only seal around the pump shaft is the air horn gasket, which isn't much of a seal. You don't really need much of a seal though because the fuel should be about 3/8" or more below the opening in the float bowl. The only way for that amount of fuel to be pouring out of that opening is for the float level to be set way too high or the needle and seat to not be sealing properly.

I would almost guarantee you either have a bad part or you messed up the assembly somewhere. I would highly recommend either a genuine AC delco rebuild kit or a specialized one for your specific quadrajet number from quadrajetparts.com or from cliffshighperformance.com

both of them are quadrajet specialists that sell known good quality parts.

 

[bigchip06]

The acc. pump seal is only in the bore and shoves fuel towards the pump shot nozzle. The only seal around the pump shaft is the air horn gasket, which isn't much of a seal. You don't really need much of a seal though because the fuel should be about 3/8" or more below the opening in the float bowl. The only way for that amount of fuel to be pouring out of that opening is for the float level to be set way too high or the needle and seat to not be sealing properly.

I would almost guarantee you either have a bad part or you messed up the assembly somewhere. I would highly recommend either a genuine AC delco rebuild kit or a specialized one for your specific quadrajet number from quadrajetparts.com or from cliffshighperformance.com

both of them are quadrajet specialists that sell known good quality parts.

You’re a genius, thank you for laying it all out. Looks like it’s almost definitely my needle and seat then. I’ll switch my old ones back in tonight and update this thread with the results. Either way I think I’m gonna end up ordering a new kit to ensure the longevity and reliability of the carb

 

[Bextreme04]

You’re a genius, thank you for laying it all out. Looks like it’s almost definitely my needle and seat then. I’ll switch my old ones back in tonight and update this thread with the results. Either way I think I’m gonna end up ordering a new kit to ensure the longevity and reliability of the carb

How are you setting your float level? You should be lightly pressing down on the back of the float arm that pushes the needle into the seat and then measuring from the lip of the float bowl to a point about 3/16" back from the tip of the float. Most quadrajets call for a bit more than 3/8" at that point. If the float is set too high, you can try setting it a little lower by putting a small rod through the vent tube and pushing down on the float... be very, very careful when doing this though

 

[fast 99]

Have seen several bad needle and seats on Holleys. Actually, just had to replace one in my car last month. A friend had a car catch fire. There are obviously some questionable parts out there. Buy name brand stuff.

 

[bigchip06]

Well, it looks like it was a little bit of everything with this one, all because of a bunk rebuild kit. I put the old needle and seat back in and it stopped leaking from the acc. pump rod, but when I was trying to tune it I noticed fuel slowly leaking from the bottom-mid layer gasket. I’m just gonna go ahead and call it there and only order top tier rebuild kits from now on. Thank you everyone for your help though, it’s much appreciated