Carb Help
Thread Starter
Instructor
Joined: Jan 2011
Posts: 111
Likes: 9
Carb Help
I have no idea what I'm doing here, and trying to learn as I go.
Purchased a carb rebuild kit, and went to work. All came apart and went back together without any issues.
However, the car will only run under very high revs / is idling very high. If I bring the idle down at all, it dies.
Any thoughts on how I need to set things / adjust something to get this thing running right?
I bought the car in January and although it wasn't running perfect, it would turn on and seemed to idle ok. I wanted to rebuild and adjust/tune to make it right, but I really am not sure what I'm doing.
Any help is much appreciated.
Working with:
1975
Crate motor (nothing special)
Holley 4150 Carburetor
Automatic car
Purchased a carb rebuild kit, and went to work. All came apart and went back together without any issues.
However, the car will only run under very high revs / is idling very high. If I bring the idle down at all, it dies.
Any thoughts on how I need to set things / adjust something to get this thing running right?
I bought the car in January and although it wasn't running perfect, it would turn on and seemed to idle ok. I wanted to rebuild and adjust/tune to make it right, but I really am not sure what I'm doing.
Any help is much appreciated.
Working with:
1975
Crate motor (nothing special)
Holley 4150 Carburetor
Automatic car
Melting Slicks
Joined: Mar 2009
Posts: 3,126
Likes: 15
Lightly, fully seat the idle mixture screws then back them out about 1 1/2 - 2 turns. If that does not do any good, I would ask if you are sure you tightened the screws that secure the bottom throttle plate to the main body. It sounds like you have a vacuum leak that is preventing enough vac. through the boosters to deliver enough fuel to let it idle. Close off the choke plate and see if it will idle then. Is carb. base gasket torn or carb. loose on intake? Also compare the bottom plate to main body gasket and make sure it is exactly like your old one. Holley kits usually have two or three gaskets and they have subtle differences. Best advice is to keep all old gaskets until you successfully complete rebuild. Just to get you started. Others will add more info. Good luck with it. mike...
Last edited by mds3013; Apr 23, 2011 at 07:18 PM.
Thread Starter
Instructor
Joined: Jan 2011
Posts: 111
Likes: 9
Lightly, fully seat the idle mixture screws then back them out about 1 1/2 - 2 turns. If that does not do any good, I would ask if you are sure you tightened the screws that secure the bottom throttle plate to the main body. It sounds like you have a vacuum leak that is preventing enough vac. through the boosters to deliver enough fuel to let it idle. Close off the choke plate and see if it will idle then. Is carb. base gasket torn or carb. loose on intake? Also compare the bottom plate to main body gasket and make sure it is exactly like your old one. Holley kits usually have two or three gaskets and they have subtle differences. Best advice is to keep all old gaskets until you successfully complete rebuild. Just to get you started. Others will add more info. Good luck with it. mike...
Couple things. I have 2 idle mixture screws (both are on the same "side" of the carb, but one on the left and one on the right). The other "side" or end of the carb has holes on each side for them it looks like, but no screws in them. Is that right?
Also, the end that does have the screws...it looks to me when we had it apart that that end doesn't actually have fuel going into it...as if it's blocked off. Is that right?
You're right about those gaskets, I'll go back and make sure it's on good, with the right base gasket.
How would I go about checking for a vacuum leak?
Thanks again.
Here's some pics for reference (prior to the rebuild and all that).
Melting Slicks
Joined: Mar 2009
Posts: 3,126
Likes: 15
I do not see anything in the pics. that is incorrect. The gasket to ck. is between the throttle shaft plate and the main body of the carb., not the carb. to intake gasket. The carb. to intake gasket of course needs to be new and like the old one also. Make sure the screws that secure throttle shaft plate to main body are tight. mike...
Safety Car
Joined: Oct 2005
Posts: 3,570
Likes: 1
From: Algonac Michigan
I can't really help you with your problem with the running condition simply by looking at the pics but I would like to suggest that you remove the glass fuel filter when you get a chance...They will leak!
Good Luck!
Good Luck!
Heel & Toe
Joined: Apr 2011
Posts: 19
Likes: 0
From: Waxahachie Texas
You can check for a vacuum leak by LIGHTLY spraying WD-40 around the base, fittings, etc. If the engine speed changes that is the leak. DO NOT get any on the exhaust, etc. This is an old-time mechanic method.
Burning Brakes
Joined: May 2008
Posts: 860
Likes: 0
From: Stratford Ontario
Check also for any lines you may have forgoten or missed. It sounds like a fairly big leak? Could be incorrect base gasket etc...
Melting Slicks
Joined: Mar 2006
Posts: 3,456
Likes: 102
From: Piedmont Va
St. Jude Donor '11-'12-'13,'19-'20
Two other things to check:
1. What is the position of your fast idle adjustment screw?
2. When you rebuilt the carb, did you mess with the secondary idle screw? If it is in too far it will cause high idle.
Good Luck!
1. What is the position of your fast idle adjustment screw?
2. When you rebuilt the carb, did you mess with the secondary idle screw? If it is in too far it will cause high idle.
Good Luck!
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Melting Slicks
Joined: Feb 2006
Posts: 3,428
Likes: 5
From: Japan
On the back side (closest to the windshield) of the carb under the secondary float bowl there should be a large vacuum fitting which is normally used for power brake boosters...can't see what that braided hose running across the back is connected to but if that fitting is open you'll have a huge vacuum leak!
Race Director
Joined: Sep 2002
Posts: 10,362
Likes: 5
From: San Diego - Deep Within The State of CONFUSION!
detents on fast idle cam in rt place? what is your vacuum reading at low idle? correct carb gtasket? Did you Match it up to be sure it was correct before installation?