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Topic: Q-jet acc pump leak

in Forum: C3 Fuel, Emission Control, and Exhaust Systems


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Q-jet acc pump leak (4/14)
 4/14/09 7:46pm
Ron 78Lifetime Member
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I agree with the other guys ,1 more thing to check,the float may have a pin hole in it and be partially filled with gas,sos it dont float right,just a thought,I've seen it happen b-4

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Q-jet acc pump leak (5/14)
 4/14/09 10:35pm
kstyerLifetime Member
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CUYAHOGA FALLS, OH - USA

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Yep, too high of a fuel level.  But the float may not be floating, or the needle and seat may not be seating.
 
Take a look at  www.vetteprojects.com  look in Ken's projects, and you will see my carb rebuild step by step with photos.   It should help.
Q-jet acc pump leak (6/14)
 4/27/09 8:57am
chris70stingray
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sykesville, MD - USA

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Well, the SOB carb builder isnt returning my phone calls, so i may have to tear into this myself. Would too high fuel pressure cause this problem too? i remember seeing something like this being the cause on one of my eldebrock 1406 installation dvd's. Also, how would i test the fuel pressure? i have a vaccum/presure testor, do i simply hook this up to a T fitting in the fuel line from the carb to the pump and start the car?
Q-jet acc pump leak (7/14)
 4/27/09 12:48pm
VetteSpecialties
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Mounds View, MN - USA

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Stock needle valves can't hold more than about five pounds pressure, but there is no need to run more than that.  If you have an aftermarket fuel pump with more pressure than that, unless you are making 500 HP and need the volume, put in the correct pump.  A work-around would be to put in a fuel pressure regulator.

Larry
Q-jet acc pump leak (8/14)
 4/27/09 1:37pm
chris70stingray
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sykesville, MD - USA

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Wow really? 5 psi, my chiltons manual says that the carb needs pressure of 7.5 to 9 psi. this sounded kinda high to me. i bought a stock replacement pump from Napa last year, maybe it is pumping out too much psi. Anyone know how to test the pressure using a gauge?
Q-jet acc pump leak (9/14)
 4/27/09 10:56pm
kstyerLifetime Member
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Just disconnect the line from the carb, and attach the pressure gauge to the line.  Crank the engine, or start it, and read the pressure.
 
5 psi is enough.
Q-jet acc pump leak (10/14)
 4/28/09 8:17am
chris70stingray
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sykesville, MD - USA

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1970 stingray coupe 270hp 350 with th400 survivor


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tested it last night, i am getting a fluctuation in the 3-5 psi. range, should i be worried about the lower range of this fluctuation (i.e. the 3-4 psi)? well the leak from the accelerator pump is a lot less this time around, but it still leaks. i noticed another leak when i turned the car off, it looked like it was coming from the gasket or a mixture screw in the base plate in the area right under the acc. pump. i have the original heat insulator? under the carb right now (intake, gasket, aluminum plate , gasket, aluminum plate, gasket, carb) i may try just throwing on one of the single thick gaskets between the intake and carb to rule out a gasket leak. i am worried that all those gaskets and plates may not be creating a good seal. thanks for all the help guys, carb diagnostics and work are still pretty new to me.
Q-jet acc pump leak (11/14)
 4/28/09 9:37pm
kstyerLifetime Member
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None of the above.  When the float level is too high you get all of what you describe.
 
Sorry, the top has to come off.  It gets adjusted, or a new float, or needle and seat.   No way around it.     
 
But try this.  Start the engine with the fuel line off and plugged.  Run it until it dies.   Reconnect the fuel line and crank then start the engine.     Sometimes some crud will get stuck in the needle and seat, and this will allow it to flush out.     If it does not cure the problem, the top of the carb comes off for repair.
 
Go to "Vetteprojects.com" and look under Ken's projects.  There is a step by step photo sequence with directions on how to rebuild a Q-Jet.   It's my carb, done on a work mat on the hood of my old Celebrity.   It should make it clear.
Q-jet acc pump leak (12/14)
 5/5/09 9:23pm
chris70stingray
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sykesville, MD - USA

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okay, i just tore it apart, no trash in the needle/seat, the float is made of foam, so no pin hole and sunk float, the float is set at 1/4 inch on the right side of the float and is a little more than 1/4 in on the left side so i guess the float is a little twisted? when i seated the needle, i notice that maybe 1 in 4 attempts the float would stick in the up postion right at the 1/4 float level, it looks like the front corners of the float are hitting the wall of the carb body. i have had a problem in the past were the car would stall and i wouldnt get any fuel to squirt all of a sudden. could this be the float sticking in the up postion and cutting off fuel to the engine? since it is a foam float does anybody see a problem with clearancing the front of the float a few thousandths so that it wont stick? anyone thinkof any other reasons why i am leaking fuel out of the acc pump plunger? if the acc pump is not adjusted right would it cause it to leak? if my mixture screws are way rich would this cause this leak? thanks in advance
Q-jet acc pump leak (13/14)
 5/5/09 11:08pm
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Don't bother with the float...go get a new one. They're about $6 or so...maybe less, depending on where you shop.
The float will soak up fuel over time, and actually swell, which will cause what you are seeing with it hanging on the carb bowl sides. If you try to trim it, or sand/grind, you'll just open up the outer shell, and expose the inner expanded foam to fuel, making an even bigger(literally) problem.
Get the carb number off of the driver side of the main bowl, just behind the linkage...it will start with a 170xxxx(or just 70). Take this number to your parts place and get a new float, install it, adjust it to the correct height, put it all back together, and drive happy.

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Q-jet acc pump leak (14/14)
 5/13/09 8:08am
chris70stingray
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sykesville, MD - USA

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1970 stingray coupe 270hp 350 with th400 survivor


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well, got a new brass float, installed it, i also found out that the clip for the needle was backwards on the float bar, so i reversed that. new base gasket, and she runs really good now, however i think i need some more tuning on the choke /fast idle, until she gets warm she runs slightly rough and a little hard to start, anyone have any good tips or artcles for tuning the fast idle on a 71 quadra? my chiltons manual sucks and doesnt really cover my specific carb i think i got the divorced choke adjustment figured out. thanks to all who have helped me out!!
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