![]() |
Register or Log In To remove these advertisements. |
|
|
![]() |
|
Thread Tools | Display Modes |
|
![]() |
#1 |
Certified Chevy Man
Join Date: Jan 2000
Location: Tucson, Arizona, United States
Posts: 2,053
|
Carb stuff, why is it doing this???
Ok, carb problems, continue. I got a 795cfm Edelbrock Q-Jet, my motor is freshly rebuilt and for some reason the carb still dribbles fuel out from the top of the primaries. I took it apart twice to check the float level and it's fine, needle and seat are fine. What could be the problem? And I don't have any sort of high volume fuel pump. If I turn the idle mixture screws all the way in, the truck still runs.
__________________
68 Chevy CST (327,TH400) 3/5 drop lots of fun stuff 71 Suburban 4x4 (350,TH350) 7" lift 37's, D44/14 bolt and other sorts of goodies, lockers front and rear, flexes 40", 895 RTI score Check out my web site!!! http://www.geocities.com/cst68chevy/ |
![]() |
![]() |
![]() |
#2 |
Registered User
Join Date: Apr 2004
Location: Grant, Alabama
Posts: 504
|
It sounds like your throttle blades are open too far for some reason and the main jets are starting to work, the reason the idle screws dont make a difference is that they aren't being used, no vacuum present at the idle passages in the throttle plate. Only thing I can think of that will do that, if the idle speed is near 1000 or less, is that you have a vacuum leak that is letting in too much air and you had to adjust the idle up high enough that the main jets are now being used to make up the difference.
__________________
72 Chevy C20, SOLD (Dang it.) 09 Challanger RT six speed in all black. 74 Datsun 710 wagon, all 1.8 liters of screaming Datsun power. 73 C10 long bed, 350/350 combo, nice shape. |
![]() |
![]() |
![]() |
#3 |
GEARHEAD
Join Date: Aug 2003
Location: MN
Posts: 6,122
|
I had this problem before too. With my original stock fuel pump it seemed to have too much pressure for the needle and seat to stop the fuel flow. I bought a Holley fuel pressure regulator and set the pressure to what stock is supposed to be and never had a problem again. This was years ago so dont ask what the pressures were, I dont remember. I'm still using the same set up though. I hope my pump lasts forever.
HG
__________________
If no one knows what you're doing, they can't tell you you're doing it wrong HG's Dream Car Build - Shelby Cobra Kit Build your own adjustable track bar 71 ![]() 72 ![]() HG's Plow Truck '78 ![]() Bigass Farm Truck HG's thread of miscellaneous stuff |
![]() |
![]() |
![]() |
#4 |
Registered User
Join Date: May 2004
Location: Canton North Carolina
Posts: 466
|
Stock Gm pump non electric should put about 5 in/ lbs of pressure to the carb many of them don't, I think average is about 3 in/lbs (may be using wrong units) but anyway anything over about 7 will blow past the stock needle and seat.
|
![]() |
![]() |
![]() |
#5 |
Certified Chevy Man
Join Date: Jan 2000
Location: Tucson, Arizona, United States
Posts: 2,053
|
I'll try the fuel pressure regulator, luckily I have one sitting out in the garage. I did this last time and set it up for 6psi, and it still did this, do I need to go to 5? I might jet the mains down a little bit too.
__________________
68 Chevy CST (327,TH400) 3/5 drop lots of fun stuff 71 Suburban 4x4 (350,TH350) 7" lift 37's, D44/14 bolt and other sorts of goodies, lockers front and rear, flexes 40", 895 RTI score Check out my web site!!! http://www.geocities.com/cst68chevy/ |
![]() |
![]() |
![]() |
#6 |
Certified Chevy Man
Join Date: Jan 2000
Location: Tucson, Arizona, United States
Posts: 2,053
|
Ok, tried the fuel pressure regulator, and took it down to 2psi and it still did it. I kinda noticed this before, but it really only is coming out from the passenger side primary. Any new ideas?
__________________
68 Chevy CST (327,TH400) 3/5 drop lots of fun stuff 71 Suburban 4x4 (350,TH350) 7" lift 37's, D44/14 bolt and other sorts of goodies, lockers front and rear, flexes 40", 895 RTI score Check out my web site!!! http://www.geocities.com/cst68chevy/ |
![]() |
![]() |
![]() |
#7 |
Old Skool Club
![]() Join Date: Jun 2001
Location: Benton, AR "The Heart of Arkansas"
Posts: 10,880
|
www.edelbrock.com
They have a technical section that lets you download manuals and trouble-shooting material. Check it out. Off-hand, I'd have to say that the float level seems suspect, but you say it isn't. You'll want to watch screwing in the idle air screws too tightly. It's easy to put a groove in the machined taper part and that will screw up your idle, too. Go to the website and check it out.
__________________
Member Nr. 2770 '96 GMC Sportside; 4.3/SLT - Daily driven....constantly needs washed. '69 C-10 SWB; 350/TH400 - in limbo The older I get, the better I was. |
![]() |
![]() |
![]() |
#8 |
Certified Chevy Man
Join Date: Jan 2000
Location: Tucson, Arizona, United States
Posts: 2,053
|
Pulled the carb off, and tried to run my other Q-Jet, but I don't have any choke or throttle linkages so that didn't work to test anything. The throttle plates on my carb seem to be open when it's at idle. By open I mean I can shine a flashlight on it and see light on the other side. Somewhere a little bit smaller than a pencil lead they are open. Could this just be sucking fuel out from the bowl?
__________________
68 Chevy CST (327,TH400) 3/5 drop lots of fun stuff 71 Suburban 4x4 (350,TH350) 7" lift 37's, D44/14 bolt and other sorts of goodies, lockers front and rear, flexes 40", 895 RTI score Check out my web site!!! http://www.geocities.com/cst68chevy/ |
![]() |
![]() |
![]() |
#9 |
Registered User
Join Date: Apr 2004
Location: Grant, Alabama
Posts: 504
|
Read my post after your original post, if the throttle plates are opened too far they idle cicuit won't function right.
__________________
72 Chevy C20, SOLD (Dang it.) 09 Challanger RT six speed in all black. 74 Datsun 710 wagon, all 1.8 liters of screaming Datsun power. 73 C10 long bed, 350/350 combo, nice shape. |
![]() |
![]() |
![]() |
#10 |
Certified Chevy Man
Join Date: Jan 2000
Location: Tucson, Arizona, United States
Posts: 2,053
|
Yeah, but should they seal all the way? And since they are open, how do you adjust them so they close?
__________________
68 Chevy CST (327,TH400) 3/5 drop lots of fun stuff 71 Suburban 4x4 (350,TH350) 7" lift 37's, D44/14 bolt and other sorts of goodies, lockers front and rear, flexes 40", 895 RTI score Check out my web site!!! http://www.geocities.com/cst68chevy/ |
![]() |
![]() |
![]() |
#11 |
Registered User
Join Date: Apr 2004
Location: Grant, Alabama
Posts: 504
|
They wont completely seal off, theres a slot where the fuel comes out but if you close them too far it will not idle either. There is a screw on the drivers side that contacts the throttle arm(where the accelrator cable is connected to). First, screw the idle mixture screws all the way in but not very hard. Back them off about 1 1/2 turns, turn the idle speed screw out until the primary blades(small ones) are just about completely closed. Put the carb back on if you havent allready. If the carb is on the intake, just back the screw back until the screw end doesnt touch the throttle arm. Make sure the chole is not on when you do this since it will be set on high idle. Easy way to do that is to pull the throttle arm back and push the choke plate all the way open then while holding it open release the throttle arm. Set the screw so that it just moves the throttle blades/shaft. Start it like you normally do, let it warm up, then kick the choke off by hitting the gas a bit. It will probably die since the blades will most likely bee too closed. Try varying the gas pedal hieght with your foot, try to get it to run at whatever idle speed you want, usually around 900 to 1000 rpm. You will at least know if it will idle then. You can then start screwing the idle speed screw in until its set. You may have to mess with the mixture screws some but 1 1/2 turns out is usually close. Set your idlke speed then turn the mixture screws in until it starts to idle rougher, back them out a bit past where it starts running smoother and then reset the speed with the idle speed screw. If that doesnt work, you have a carb problem or a vacuum leak somewhere. Its kind of hard to diagnose over a forum, lol.
__________________
72 Chevy C20, SOLD (Dang it.) 09 Challanger RT six speed in all black. 74 Datsun 710 wagon, all 1.8 liters of screaming Datsun power. 73 C10 long bed, 350/350 combo, nice shape. |
![]() |
![]() |
![]() |
#12 |
Certified Chevy Man
Join Date: Jan 2000
Location: Tucson, Arizona, United States
Posts: 2,053
|
I'm probably done what you've said a million times. Problem is at anything less on the idle screw the truck won't run.
__________________
68 Chevy CST (327,TH400) 3/5 drop lots of fun stuff 71 Suburban 4x4 (350,TH350) 7" lift 37's, D44/14 bolt and other sorts of goodies, lockers front and rear, flexes 40", 895 RTI score Check out my web site!!! http://www.geocities.com/cst68chevy/ |
![]() |
![]() |
![]() |
#13 |
Registered User
Join Date: Apr 2004
Location: Grant, Alabama
Posts: 504
|
Hows your timing? Are the idle air jets and fuel passages cleaned out? Have you checked for any kind of vacuum leaks?
__________________
72 Chevy C20, SOLD (Dang it.) 09 Challanger RT six speed in all black. 74 Datsun 710 wagon, all 1.8 liters of screaming Datsun power. 73 C10 long bed, 350/350 combo, nice shape. |
![]() |
![]() |
![]() |
#14 |
blood type; Retumbo
Join Date: Jan 2004
Location: next to my reloading bench
Posts: 10,269
|
just for reference the transfer slots should have 0.040" underneath the blades. more than that & you will be drawing from the main ckt.
is there a vac leak on the pass. side of carb? use propane to find leak. is pass. blade bent?
__________________
Man rule #77...if you own a 67 stepside with a caddy 472 you will never be in danger of loosing you man card |
![]() |
![]() |
![]() |
#15 |
Registered User
Join Date: Mar 2000
Location: Blue Ridge, Tx
Posts: 1,172
|
Could be symptoms of a bad float. Check for small pin holes in the floats or if they are full of fuel.
__________________
Fawker Fab three seater rock crawler buggy 498 BBC/SM465/203/205 doubler, propane, 5.13's, 42" PB Rockers '66 C10 - The new hot rod '77 3+3 Dually - 12 valve 4wd conversion tow rig project '28 Ford 2 door sedan street rod RevLimit Offroad "Hang on beer, we can do this." |
![]() |
![]() |
![]() |
Bookmarks |
Thread Tools | |
Display Modes | |
|
|