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I have a 1985 gmc Sierra with an 305 with an edelbrock 1401 500cfm carb how should I adjust the carb to run stronger with the 2 screws on the front of the carb

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Start by checking the existing settings of your air adjusting screws (the two in front). you do that by turning the screws one at a time in (clock wise) at one half turn at a time until they stop. should be appx. 1 1/2 turns. Be sure to jot down how many turns it took so you can put them back if need be. Now set both at 1 1/2 turns out (counter clock wise) NOTE. Do all this with engine off...... Now start engine and turn screws out slowly one at a time about 1/2 turn then in until you hear the engines RPMs start to drop then turn out again 1/4 turn. Now your air/fuel mixture should be as close as your going to get it without a dino machine

Posted on Jan 03, 2013


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SOURCE: 1985 gmc sierra shakes

Sounds to me to be a timming issue like maybe retarted, also chk. to see if the wire is pluged in by dist, the wire that you have to unplug when your going to time it, i can't remember what its called. There is only 2 things on this truck thats controled by the computer is spark and fuel, if that wire is unpluged by dist. it will run like that, unless someone has changed it back to the old style dist. and carb. if thats the case loosen dist. and move it a little and see if it dosent run better, clockwise advance, counter clockwise is retarded.

Posted on Feb 26, 2009

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SOURCE: 1998 GMC Sierra (C1500) 5.0L 305 V8-right rear brake line

i dont know of any recall for that
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Posted on Apr 20, 2009

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SOURCE: smoking 305 motor

Time to rebuild the engine. Your piston rings, main bearings, connecting rod bearings, camshaft bearings, and valve guides in the cylinder heads, are worn out. Possibly the shafts are worn on the valves, and the piston skirts also. (Means new valves, and pistons, plus boring and honing the block. You'll need a new oil pump, gaskets, freeze plugs, spark plugs, oil and filter, for a few more things to add to the list)

What you are seeing is called 'Blowby'. This is a normal thing with a worn out engine.
Also replace the PCV valve as it is probably clogged up. (Positive Crankcase Ventilation Valve)

Posted on Sep 02, 2009

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SOURCE: my 1985 chevy 305 gets 4mi to the gallon

Check your ignition timing at 3500 rpm you should have about 40 degrees of advance If not, something is sticking in the distributor, either the vacuum or mechanical advance. This will cause a big reduction in fuel economy. Also, check your tire pressure. The cfm on a rochester is really not important. The primary bores are so small and they are the only thing allowing the mixture in most of the time.

Posted on Jan 29, 2010

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Hi I just want to how much easier is it to tune an edelbrock carb then a quadrajet carb

Edelbrock cars are square bore and Quadrajets are spreadbore make sure you have either an adaptor plate if running stock manifold or you'll have vacuum leaks, as far as tuning Edelbrocks are EZ. 2 air/fuels screws that only effect idle, turn in till runs rough then back out 1/4 to 1/2 turn on both, that will set it for economy, for performance engines, turn out or counter clockwise till runs rough then turn back in clockwise 1/2 to full turn, set idle ***** and your good to go, the two vacuum ports in front are distributor advance, the right side closest to manifold is full time vacuum hook there for performance or left side for economy.. if you buy a new edelbrock carb it will run great right out of the box, also has a set/up DVD, for novice Mechanics, ez to change metering rods too, hope this helps, and in my opinion Quadrapuke carbs are junk.

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I own a 1977 GMC Sierra C25 with a 5.0L V8 305 cu in. I would like to know what each of the two screws on the front of my carburetor are.

Down low at the base near the intake manifold are two slender pointed air/fuel mixture screws with springs on them. While running at idle, Turn them in until it starves and almost dies at idle then back out 1/4 turn. Usually out from closed stop about 1 1/2 turns.

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on this truck the vacuum is pretty basic, im guessing you have a 305 (5.0) or a 350 (5.7), on the front of the engine compartment near the fan shroud somewhere (if it is still intact) you should have a diagram of all the vac lines
you probably have a quadrajet carb, if you are mechanical and patient they are not hard to rebuild

blowing out the carb with carb and choke cleaner isnt a bad idea either, have someone keep it running and slowly run like 1/4 to 1/2 a can down the carb spraying all around

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1 Answer


High HC counts are due to a rich mixture, too much fuel. How does the truck run normally? To adjust the fuel mixture at the carburetor, make sure the truck is at operating temperature. Turn the idle mixture screw clockwise until the engine starts to lag then turn the screw back just until it runs smooth. Also make sure you have fresh oil as this could cause high HC's as well since fuel gets into the oil and make sure your PCV valve is operating correctly. If you can't get it adjusted correctly, you may have to pay a shop to hook it up to the emissions machine to get the mixture correct, unfortunately.
Hope this helps. Good luck!

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I need to adjust my qcarb on 1985 gmc-pickup two wheel drive . i need to know what evey screw does

this truck doesnt have a carb, this has a throttle body, its fuel injected,there are no adjustments,every adjustment is done from the factory, the computer controls the idle,trying to raise the idle will throw the tps readings off,

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Should I rebuild my Ford Bronco 351 Windsor Holly 4 bbl carb or replace it with an Edelbrock carb?

In all my experience, if you know how to correctly tune a edelbrock then go with that, but, holley has outstanding carbs that can muster up to an output of 1,200hp. it would be much cheaper to et a rebuild kit from say, o'reillys, 20-45 dollars depending on which one you have.
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You may have an internal carb gasket leak or your floats may be adjusted too high.After you run the truck look into the carb to see if there is gas still dripping into the carb bore.Also after running with engine on remove the front fuel level check screw. (have lots of rags under to catch fuel) Fuel level should be right below hole.If it is spilling out it is too high.Floats need to be adjusted up for fuel level to go down.

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Oil pressure problem

there is no oil up in the intake area so its nothing you could have done BUT the oil pressure reading comes from the oil pressure sending unit near the dist. housing. you had to remove the dist. when changing the intake so maybe the sensor or it's connection are loose.
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2 Answers

1985 gmc sierra shakes

Nic, If the carburetor was dumping gas, remove the engine oil dip stick and see if it smells like gasoline. If it does you will need to change the oil.
Second, go back over your spark plug wires and verify they are on the correct spark plug. Start with the #1 plug wire, the firing order is 1,8,
Let me know how it turns out and we can go from there.
Good luck.

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