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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 (1/14)
 4/14/09 10:48am
chris70stingray
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sykesville, MD - USA

Vette(s):
1970 stingray coupe 270hp 350 with th400 survivor


Joined: 4/14/2009
Posts: 13

Hey guys, newbie here, i have a late year 1970 270hp 350 with a early year 71 engine and q-jet (original from factory) 40 some thousand miles, car was sitting for 20 years, started up every few years, i am in the process of restoring her and am running into a bad accelerator pump leak. i had the carb rebuilt last fall by a carb guy, ( will be calling him later today but wanted to pass this by some vette guys too) she will start up fine and high idle at 1000 rpm with no leak but after she iswarm and you give her a rev or too to get off of high idle she will stumble around 4-500 rpm and leak like a sive aroundthe plunger for the acc pump. ihave had her running good last fall and set the idle then around 700 rpm. realy havent put any miles on the rebuilt carb, some things to note are:
 
new gas tank a few years ago
new fuel pump and hoses
blew out fuel lines with compressed air
new filter
 
i have had another issue last fall with this carb too, i guess the needle and seat were sticking because the car would stall and not squirt fuel even though no blockages in the filter etc. had the carb builder put in a new needle and seat and it seemed to have helped, but now i have this issue, any thoughts? too much fuel pressure? thanks in advance
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Q-jet acc pump leak (2/14)
 4/14/09 11:37am
VetteSpecialties
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Mounds View, MN - USA

Vette(s):
70 LT1 coupe, 69 350 HP coupe, 69 390HP 427 coupe, 71 LS5 convert, 85 coupe, 93 coupe


Joined: 5/24/2007
Posts: 1031

The only way fuel can be around the top of the pump plunger is if the fuel level is too high.  It sounds like your needle and seat are leaking again.  Either you didn't get a good quality one before, or there is junk in your fuel system that gets in the seat.

Larry
Q-jet acc pump leak (3/14)
 4/14/09 1:01pm
Adams' AppleLifetime Member
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Duncanville, TX - USA

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#1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas


Joined: 11/8/2003
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I agree with Larry...the fuel level is too high. At higher idle/engine speed, the engine can handle the extra fuel, but not at normal idle. As Larry says, the only way for fuel to run out thru the acc. pump hole is for it to be too high to start with.
So....either the float is sticking, or not set properly, or there is some trash in the needle/seat assy that is not allowing the needle to fully seat, and shut off the fuel flow.
Whatever the problem is, it is definitely inside the carb, from the description.

btw...Welcome to C3VR!!!Adams' Apple2009-04-14 10:02:47

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Q-jet acc pump leak (4/14)
 4/14/09 7:46pm
Ron 78Lifetime Member
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BINGHAMTON, NY - USA

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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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1975 C3 Red, T-Tops, Black Interior. All I need is time and money! Getting there!


Joined: 12/2/2003
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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

Vette(s):
1970 stingray coupe 270hp 350 with th400 survivor


Joined: 4/14/2009
Posts: 13

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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70 LT1 coupe, 69 350 HP coupe, 69 390HP 427 coupe, 71 LS5 convert, 85 coupe, 93 coupe


Joined: 5/24/2007
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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

Vette(s):
1970 stingray coupe 270hp 350 with th400 survivor


Joined: 4/14/2009
Posts: 13

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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CUYAHOGA FALLS, OH - USA

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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

Vette(s):
1970 stingray coupe 270hp 350 with th400 survivor


Joined: 4/14/2009
Posts: 13

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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CUYAHOGA FALLS, OH - USA

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1975 C3 Red, T-Tops, Black Interior. All I need is time and money! Getting there!


Joined: 12/2/2003
Posts: 6424

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

Vette(s):
1970 stingray coupe 270hp 350 with th400 survivor


Joined: 4/14/2009
Posts: 13

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
Adams' AppleLifetime Member
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Duncanville, TX - USA

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#1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas


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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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Joel Adams
C3VR Lifetime Member #56    

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             NCRS

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Q-jet acc pump leak (14/14)
 5/13/09 8:08am
chris70stingray
Former Member

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sykesville, MD - USA

Vette(s):
1970 stingray coupe 270hp 350 with th400 survivor


Joined: 4/14/2009
Posts: 13

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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