1970 Chevrolet Impala Sedan 350 V8 5.7 Liter - Chevy Impala Forums
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post #1 of (permalink) Old 05-25-2017, 06:09 AM Thread Starter
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1970 Chevrolet Impala Sedan 350 V8 5.7 Liter

My Impala has a small problem starting up. It will start on some occasions, but most of the time it will turn off after a couple of seconds. I know it can't be the spark plugs/wires because I replaced those. It starts like a cold engine, even when it's hot out.
I thought it might be the starter having problems? But my dad says it couldn't be the starter.
Anyone have any ideas?

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post #2 of (permalink) Old 05-28-2017, 06:56 AM
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Coil/Cap/Fuel Filter(s) /Fuel pump pressure ?

Any 1 or combination of those things can cause this.

Some things are better left unsaid, which I generally realize right after I have said them.
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post #3 of (permalink) Old 05-28-2017, 12:15 PM
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On a mechanical fuel pump carbed setup would fuel pressure be an issue at idle or startup? Thought the car basically ran off the float bowl at startup? Carbs aren't my thing so I am asking.

It this a sudden failure or did you buy the car like this? Is it driveable atall?

Old carbs aren't necessarily a bad thing but what people who don't know what they are doing have done to the carb over the decades can definitely be a bad thing.

If it is starting then shutting off that is not the starter. If it is cranking slowly causing the hard start that can be a bad starter.


I might start with grounds and connections. Both battery posts, starter connections, ground strap from engine to chassis cleaned on both ends. If not familiar with working with this stuff do some reading first. make sure the negative is disconnected when working with the positive especially the positive at the starter as the cable can bump into things and weld itself to something then overheat and melt things potentially burning you or starting a fire.

It may well be a fuel delivery issue too but you sound like a novice and some cursory electrical connection cleaning is a safer place to start.

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post #4 of (permalink) Old 05-28-2017, 03:48 PM
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Correct.
I guess it was still mechanical fuel pumps back then. There is a filter I believe at the inlet of the carb built into the base. You have to remove the inlet line and use a 1" wrench to access that filter. Some had a bronze filter and some had a paper element about inch and half long. That's one thing to check.
When the car is running will it accelerate to max rpm and pull all gears without lying down ?

Some things are better left unsaid, which I generally realize right after I have said them.
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post #5 of (permalink) Old 06-02-2017, 02:20 PM Thread Starter
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She runs pretty good, quite fine, actually for her age. It's just starting it up is where the major problem lies.

It's not about how much money you put into a car, it's about how much time and effort you put in it.
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post #6 of (permalink) Old 06-02-2017, 02:43 PM
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If the gas is not more than a few months old, I'd say you need to rebuild the carb, or buy a rebuilt one and trade in yours as a core, AFTER you install the new one and know it runs well, perhaps taking any parts off that need to swap, like maybe choke parts.

Floats get heavy, needle and seats deteriorate, passages plug, it's more than likely the original carb, and nearly 60 years old. Even if they changed it 30 years ago, ya know, it's nearly 30 more years on the new one.

Cars this old need all the possible issues gone thru, and then kept up in good shape. Or you won't have a reliable car. Gas filter is in the carb.

Who knows how much crap is in the gas tank. Me, I'd pull it, dump it out, reinstall it, put new gas in it, and rebuild or get a rebuilt carb. You probably just want it to run the easiest, quickest way.

If the fuel pump is able to provide gas for it to start, it should at least idle. Is the choke valve shutting so it can run right at start up, cold?

The think is, none of us know anything about the condition of your car to diagnose what is or isn't wrong.

You start ruling things out, and you may find it's a bunch of little things, that all need to be brought newer again.
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post #7 of (permalink) Old 06-02-2017, 02:46 PM
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Carb ever been rebuilt? Leaky needle and seat?
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post #8 of (permalink) Old 06-02-2017, 04:42 PM
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If it starts and runs then shuts off the starter is not the problem.

Think Bill is right on track too with the idea of rebuilding the carb.

My 6 year constantly asks why. What adults can learn from 5 and 6 year olds, to listen with your ears and mind open. Hard to learn when you don't listen ......
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post #9 of (permalink) Old 06-02-2017, 10:50 PM
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Quote:
Originally Posted by 350 View Post
My Impala has a small problem starting up. It will start on some occasions, but most of the time it will turn off after a couple of seconds. I know it can't be the spark plugs/wires because I replaced those. It starts like a cold engine, even when it's hot out.
I thought it might be the starter having problems? But my dad says it couldn't be the starter.
Anyone have any ideas?

You did not mention if the engine is period correct with a carburetor, or a replacement engine with fuel injection. My father purchased a new 1971 Impala 4-door with the 350 engine, that I used to help maintain when I was a teenager. If I remember correctly, a two or four barrel carburetor was offered in 1971. If carbureted:

Problem areas:

1. Choke pull-off - check vacuum line to pull-off and if pull off vacuum diaphram is leaking.

2. Vacuum leak around base of carburetor - see if four bolts holding carburetor to intake manifold are tight.

3. High speed idle screw / cam adjustment - is it set correctly?

4. When you depress the pedal, does the primary butterfly valve shut completely due to the choke closing? The choke plate should open about 1/8 inch when the car starts - and then quickly open as the choke coil heats.

5. Does your model year have a carburetor solenoid? If so, does the plunger extend when the ignition switch is turned to "on" and the accelerator pedal pressed?
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post #10 of (permalink) Old 06-06-2017, 12:57 AM Thread Starter
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My dad does think that the Carburetor is the problem due to it have some problems with starting after a couple of times trying to start it and trying to start it after driving around, turning it off, and trying to start it.
I have thought about purchasing a new carburetor but I don't know which brand is better, Holley or Edelbrock. Or what I need to look for, for a 2bbl Carburetor.

It's not about how much money you put into a car, it's about how much time and effort you put in it.
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post #11 of (permalink) Old 06-06-2017, 06:49 AM
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I would stick with a Quadrajet carb.


People who drive slower than me are Assholes.
People who drive faster than me are Crazy.
http://www.crateenginedepot.com/350-...09-P10380.aspx

1983 Caprice Classic. 350 CID. 330 HP. 380 Ft.Lbs. Torque. Turbo 350 Trans. with Cooler.
Quadrajet Carb. Headman Headers. Magnaflow Cats. Flowmaster Delta 50 Mufflers.
Electric Fan. Compu Star Alarm. Two-way dash-cam. Crazy Canuck behind the Wheel.

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