1975 Chevy 3/4 ton - hard to start cold

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  #1  
Old 06-06-02, 04:42 AM
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1975 Chevy 3/4 ton - hard to start cold

1975 Chevy 3/4 ton 4x4 with 350 engine. Approx 160,000 miles.

Hard to start when cold and wont idle until good and warmed up.
Otherwise engine runs good, produces good power.

I am going to replace the fuel filter and run some carb cleaner through the system, however, I am thinking the carb needs some tinkering. I have never done any carb work, is it difficult and will it be covered in Chilton manual (if one exists)?
 
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  #2  
Old 06-06-02, 05:23 AM
redneck
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If it still has the stock carb. it is your choke. They had heat activated spring type choke back then--you could retrofit an electric choke kit--but I would convert yours to a manual cable operated type.
 
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Old 06-06-02, 05:43 AM
Joe_F
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I agree. Rebuilt carburetor time. Any parts store will be able to supply the needed parts for it to be rebuilt.

Make sure the vehicle is also tuned up at the same time.
 
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Old 06-06-02, 06:08 AM
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The engine was recently tuned (new plugs, wires, distributer). Having never done any carb work, how tough is it to rebuild one?

What is the choke doing that makes the engine hard to start (staying open, staying closed??)

Is there anything I can do in the mean time to make it easier to start?
 
  #5  
Old 06-06-02, 06:34 AM
Joe_F
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Likely staying closed.

Take off the air filter cover. Start out first thing in the morning, letting it sit overnight.

Pump the pedal to the floor once or twice slowly. The choke should close almost all the way. Start it up. The flap should be open about an 1/8" of an inch, 1/4 of an inch. Let the truck warm up. Watch the choke flap. If it always stays closed, you likely have a bad choke thermostat or a wiped out pull off.

Either is easy to change, but you should get a repair manual (14 bucks at the parts store, free at the library) to guide you through the adjustment procedures on them.

Again, the carburetor is likely tired and should be completely overhauled with all new parts. The rebuilding kit comes with instructions. You might pick up a spare core at the junkyard with the same casting/tag # and practice there first. If you succeed, swap it to the truck and use that one.
 
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Old 06-06-02, 11:16 AM
redneck
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I have to disagree on this one. All the rebuild kits I have ever installed do not address the choke. If the truck runs fine when warmed up then the carb is functioning properly. Also, if the choke was staying closed it would start fine and then run rough after warm up--just the opposite of this persons truck. I believe the choke is open and not closing automatically as it should when cold.
 
  #7  
Old 06-06-02, 12:49 PM
Joe_F
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I can bet on a truck this old, you've got:

1) An old and tired needle and seat.
2) A soggy float
3) Weak choke pull off
4) Lazy choke thermostat
5) Crusty and dried out gaskets
6) Out of adjustment mixture screws.

Bearing that in mind, and considering if you do it yourself, you're probably looking at 60 bucks in parts to do the whole thing. It will run like new if you do it right and give you less trouble.

My .02. Pay now or do it again later .
 
  #8  
Old 06-07-02, 09:35 PM
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Choke is not closing

I agree with redneck it sounds like your choke spring is shot and not closing your choke flap when cold.

Rebuilding a Carbarator is a walk in the park, you did not say if it was a 2 or 4 barrel but both are not hard at all.

There are many good carbarator rebuild books out amoung the parts stores. Most of your rebuild will be cleaning the passage ways and body. Make sure you place a new part that is just like the old part next to each other.

The reason for that is sometimes the kit has different gaskets and small parts. When you match part for part you never have to guess. Just keep all your parts in seprate places in the order they came off.

After your first carb rebuild you will want to do a rebuild once a year. Believe me after a lifetime rebuilding carbs the fuel you save with a yearly rebuild, will more than make up for the cost of the new kit.

Standard Moter Products makes the best rebuild kit & Tomco makes the worst. Buy a new float as the kits don't come with floats anymore. Also replace your choke rinkedos with a good manual choke cable, and you will allways know that your choke is working.

You can do it your'e a DIYer
Marturo
 
  #9  
Old 06-07-02, 11:19 PM
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Don't the 70's Chevys have the old black plastic plate choke adjustment on the left side of the carb? Sounds to me like the choke's staying open if its hard to start (and runs well when warm). A closed choke should start a cold engine right up. Do like Joe says and get the book on your truck before you go spend too much on a carb or kit. With 160K on a 4X4 it looks like you take pretty good care of it.
Let us know what you do and how it worked!
 
  #10  
Old 06-10-02, 05:02 AM
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There is a pin, actuated by the throttle, on top of the carb that opens the choke. The pin was sticking leaving the choke open. I took some carb cleaner and cleaned it up real good, works like a charm. I am going to replace the choke spring as well. Thanks everyone for all the insight, doubt I would have figured this one out without you guys!
 
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