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Old 05-31-2021, 11:15 AM   #1
Captain J
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Rochester QuadraJet 4bbl Carburetor issue

Hello
My truck (1986 GMC Sierra K2500 with 5.7L) have issues with starting, engine will crank but itíll not start, I replaced the fuel tanks, new sending units, new fuel hoses, new fuel pump, new fuel filter, rebuild the stock carburetor (Rochester QuadraJet 4bbl), fuel comes to the carburetor.
Issue:
It will start if I put fuel in the carburetor for the 1st of the day, subsequent starts are ok. If I leave the truck overnight, next day itíll not start (itíll crank, but no start).
Need help
Thanks
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1972 GMC Sierra C2500, V8-350
1986 GMC Sierra C2500, V8-454
1986 GMC Sierra C2500, V8-LS1
1986 GMC Sierra K2500, V8-350
1987 GMC Sierra R3500, V8-454
1997 GMC Sierra K2500, V8-454
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Old 05-31-2021, 11:23 AM   #2
geezer#99
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Re: Rochester QuadraJet 4bbl Carburetor issue

If filter in carb was replaced was it installed right?
Sorry, delete that question. Filter must be good from your description.
Does your choke work?
Any fuel from the accelerator pump when you pump it first time when cold?
Could be leaking fuel bowl wells also.
That’s not normally a problem with your carb though.

How new is the fuel pump?

Last edited by geezer#99; 05-31-2021 at 12:10 PM.
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Old 05-31-2021, 12:49 PM   #3
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Re: Rochester QuadraJet 4bbl Carburetor issue

Quote:
Originally Posted by geezer#99 View Post
If filter in carb was replaced was it installed right?
Sorry, delete that question. Filter must be good from your description.
Does your choke work?
Any fuel from the accelerator pump when you pump it first time when cold?
Could be leaking fuel bowl wells also.
Thatís not normally a problem with your carb though.

How new is the fuel pump?
Thanks for replying
Filter is installed correctly,
Choke is electrical but how do I test it? Because it starts no idle after starting,
Not sure about the accelerator pump, do I look inside the primary to see if fuel comes out?
Fuel pump is less than a month old (brand new)
I didnít do the rebuild myself, someone else did it.
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1972 GMC Sierra C2500, V8-350
1986 GMC Sierra C2500, V8-454
1986 GMC Sierra C2500, V8-LS1
1986 GMC Sierra K2500, V8-350
1987 GMC Sierra R3500, V8-454
1997 GMC Sierra K2500, V8-454
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Old 05-31-2021, 01:00 PM   #4
geezer#99
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Re: Rochester QuadraJet 4bbl Carburetor issue

Yup!
Look in the carb. Hold the choke blade wide open. Stroke the throttle quickly. Look for fuel beside the boosters. Up near the top front. Should see two shots. One on each booster.
To check choke open throttle 1/4 way and choke flap should move and close off top of primaries.
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Old 05-31-2021, 01:14 PM   #5
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Re: Rochester QuadraJet 4bbl Carburetor issue

Quote:
Originally Posted by geezer#99 View Post
Yup!
Look in the carb. Hold the choke blade wide open. Stroke the throttle quickly. Look for fuel beside the boosters. Up near the top front. Should see two shots. One on each booster.
Ok 👍🏻
To check choke open throttle 1/4 way and choke flap should move and close off top of primaries.
Is that with ignition off or on?
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1972 GMC Sierra C2500, V8-350
1986 GMC Sierra C2500, V8-454
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Old 05-31-2021, 01:18 PM   #6
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Re: Rochester QuadraJet 4bbl Carburetor issue

Off.
Sometimes easier to use a small flashlight to see inside the carb.
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Old 05-31-2021, 01:45 PM   #7
Captain J
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Re: Rochester QuadraJet 4bbl Carburetor issue

Quote:
Originally Posted by geezer#99 View Post
Off.
Sometimes easier to use a small flashlight to see inside the carb.
Ok
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1972 GMC Sierra C2500, V8-350
1986 GMC Sierra C2500, V8-454
1986 GMC Sierra C2500, V8-LS1
1986 GMC Sierra K2500, V8-350
1987 GMC Sierra R3500, V8-454
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Old 06-01-2021, 10:42 AM   #8
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Re: Rochester QuadraJet 4bbl Carburetor issue

Quote:
Originally Posted by geezer#99 View Post
Off.
Sometimes easier to use a small flashlight to see inside the carb.
Update
Iíve not started the truck for the past 5 days,
Today before starting I checked to see if i can see fuel is squirting inside the carb if I push the paddle, and it did.
So I cranked the car, fuel stopped squirting,
So I waited for few minutes I repeated the process
Pushing the paddle without cranking, and nothing, no fuel coming
Iíll check after few hours.
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1972 GMC Sierra C2500, V8-350
1986 GMC Sierra C2500, V8-454
1986 GMC Sierra C2500, V8-LS1
1986 GMC Sierra K2500, V8-350
1987 GMC Sierra R3500, V8-454
1997 GMC Sierra K2500, V8-454
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Old 06-01-2021, 10:53 AM   #9
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Re: Rochester QuadraJet 4bbl Carburetor issue

It only squirts when you stroke the throttle
It should squirt every time you stroke it.
If not (like in your second test), then the pump well is low, float level is low. And possibly the check ball is stuck.
Will the choke blade close when you stroke the throttle?
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Old 06-01-2021, 11:13 AM   #10
Wgesnerjr
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Re: Rochester QuadraJet 4bbl Carburetor issue

IIRC, there is a spring in with the fuel filter. Make sure you have it on the correct side of the filter. Also double check that the filter is going the right way.

I did this once when I was young and had to pay a mechanic to put it in right.

If you have a paper filter make sure the end with the hole is going towards the fuel line, opposite the spring.
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Old 06-01-2021, 11:19 AM   #11
Captain J
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Re: Rochester QuadraJet 4bbl Carburetor issue

Quote:
Originally Posted by geezer#99 View Post
It only squirts when you stroke the throttle
It should squirt every time you stroke it.
If not (like in your second test), then the pump well is low, float level is low. And possibly the check ball is stuck.
Will the choke blade close when you stroke the throttle?
The choke blade was wide open before I do the test, and stayed open while I moving the throttle.
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1972 GMC Sierra C2500, V8-350
1986 GMC Sierra C2500, V8-454
1986 GMC Sierra C2500, V8-LS1
1986 GMC Sierra K2500, V8-350
1987 GMC Sierra R3500, V8-454
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Old 06-01-2021, 11:21 AM   #12
kwmech
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Re: Rochester QuadraJet 4bbl Carburetor issue

Well plugs in the bottom of the bowl could be draining overnight. Quite common area to fix when rebuilding the carb. Mix up some JB weld--apply and wait a few hours
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Old 06-01-2021, 11:21 AM   #13
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Re: Rochester QuadraJet 4bbl Carburetor issue

Quote:
Originally Posted by Wgesnerjr View Post
IIRC, there is a spring in with the fuel filter. Make sure you have it on the correct side of the filter. Also double check that the filter is going the right way.

I did this once when I was young and had to pay a mechanic to put it in right.

If you have a paper filter make sure the end with the hole is going towards the fuel line, opposite the spring.
Iím positive itís, but I rechecked it aging,
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1972 GMC Sierra C2500, V8-350
1986 GMC Sierra C2500, V8-454
1986 GMC Sierra C2500, V8-LS1
1986 GMC Sierra K2500, V8-350
1987 GMC Sierra R3500, V8-454
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Old 06-01-2021, 11:36 AM   #14
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Re: Rochester QuadraJet 4bbl Carburetor issue

Quote:
Originally Posted by Captain J View Post
The choke blade was wide open before I do the test, and stayed open while I moving the throttle.
Should have closed.
We’ll help fix that but first a question.
When you do get it running and when driving down the road and you step on the pedal, do you feel a slight stumble?
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Old 06-01-2021, 11:47 AM   #15
Captain J
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Re: Rochester QuadraJet 4bbl Carburetor issue

Quote:
Originally Posted by kwmech View Post
Well plugs in the bottom of the bowl could be draining overnight. Quite common area to fix when rebuilding the carb. Mix up some JB weld--apply and wait a few hours
Thatís something Iíll do thanks
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1972 GMC Sierra C2500, V8-350
1986 GMC Sierra C2500, V8-454
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1986 GMC Sierra K2500, V8-350
1987 GMC Sierra R3500, V8-454
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Old 06-01-2021, 11:48 AM   #16
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Re: Rochester QuadraJet 4bbl Carburetor issue

Quote:
Originally Posted by geezer#99 View Post
Should have closed.
Weíll help fix that but first a question.
When you do get it running and when driving down the road and you step on the pedal, do you feel a slight stumble?
No, it runs fine, subsequent starts are also ok
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1972 GMC Sierra C2500, V8-350
1986 GMC Sierra C2500, V8-454
1986 GMC Sierra C2500, V8-LS1
1986 GMC Sierra K2500, V8-350
1987 GMC Sierra R3500, V8-454
1997 GMC Sierra K2500, V8-454
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Old 06-01-2021, 12:08 PM   #17
geezer#99
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Re: Rochester QuadraJet 4bbl Carburetor issue

The black cap on the side of the carb should have 3 screws on it. Loosen them and rotate the cap counter clockwise. Hold the throttle open and the choke blade should close. Turn it until it just closes then tighten the screws.
That should help starting.
I’d do that first.
If it helps the no start situation then you know the well are good.
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Old 06-01-2021, 01:17 PM   #18
Captain J
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Re: Rochester QuadraJet 4bbl Carburetor issue

Quote:
Originally Posted by geezer#99 View Post
The black cap on the side of the carb should have 3 screws on it. Loosen them and rotate the cap counter clockwise. Hold the throttle open and the choke blade should close. Turn it until it just closes then tighten the screws.
That should help starting.
Iíd do that first.
If it helps the no start situation then you know the well are good.
Ok, thanks
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1972 GMC Sierra C2500, V8-350
1986 GMC Sierra C2500, V8-454
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1986 GMC Sierra K2500, V8-350
1987 GMC Sierra R3500, V8-454
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Old 06-01-2021, 02:50 PM   #19
Captain J
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Re: Rochester QuadraJet 4bbl Carburetor issue

Quote:
Originally Posted by geezer#99 View Post
The black cap on the side of the carb should have 3 screws on it. Loosen them and rotate the cap counter clockwise. Hold the throttle open and the choke blade should close. Turn it until it just closes then tighten the screws.
That should help starting.
Iíd do that first.
If it helps the no start situation then you know the well are good.
Updates

The fuel pump works,
The fuel filter is correct

I turned the choke cap to the left, it only turned less than 1/4 turn.
Truck started but with stuck full throttle, I shut down.
I checked the throttle cables theyíre ok, throttle moves ok, gas paddle moves ok.
Started again, full throttle.
I moved the choke cab back to where it was,
started again, full throttle, shut it down,

So I gave up, 😡😤
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1972 GMC Sierra C2500, V8-350
1986 GMC Sierra C2500, V8-454
1986 GMC Sierra C2500, V8-LS1
1986 GMC Sierra K2500, V8-350
1987 GMC Sierra R3500, V8-454
1997 GMC Sierra K2500, V8-454
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Old 06-01-2021, 03:43 PM   #20
geezer#99
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Re: Rochester QuadraJet 4bbl Carburetor issue

It’s likely still on high idle.
There’s a high idle screw under the choke pull off pot on the front passenger side.
It’s a Phillips head screw. A little hard to see.

Rotate it ccw a couple turns and try again.
See how that works.
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Old 06-02-2021, 10:21 AM   #21
Captain J
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Re: Rochester QuadraJet 4bbl Carburetor issue

I’ll tonight and see what happen,

Question
Where can I buy stock or rebuilt Rochester QuadraJet 4bbl for 1986 GMC Sierra C/K2500 with 5.7/7.4L engines?
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1972 GMC Sierra C2500, V8-350
1986 GMC Sierra C2500, V8-454
1986 GMC Sierra C2500, V8-LS1
1986 GMC Sierra K2500, V8-350
1987 GMC Sierra R3500, V8-454
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Old 06-02-2021, 10:32 AM   #22
geezer#99
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Re: Rochester QuadraJet 4bbl Carburetor issue

What’s your budget like?

Any rebuilt might not run very well. Depending on your carbs original set up. Different jetting, rods, etc.

Can you post a pic of yours?
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Old 06-02-2021, 11:03 AM   #23
Captain J
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Re: Rochester QuadraJet 4bbl Carburetor issue

It took more than 4 ccw to get the idle correct, truck started for the 1st time without any help 😁 thanks to you all for the help

Pictures will be uploaded shortly
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1972 GMC Sierra C2500, V8-350
1986 GMC Sierra C2500, V8-454
1986 GMC Sierra C2500, V8-LS1
1986 GMC Sierra K2500, V8-350
1987 GMC Sierra R3500, V8-454
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Old 06-02-2021, 11:13 AM   #24
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Re: Rochester QuadraJet 4bbl Carburetor issue

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Old 06-02-2021, 11:14 AM   #25
geezer#99
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Re: Rochester QuadraJet 4bbl Carburetor issue

Awesome!
Where in the world do you live?
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