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-   -   Rochester QuadraJet 4bbl Carburetor issue (https://67-72chevytrucks.com/vboard/showthread.php?t=822306)

Captain J 05-31-2021 11:15 AM

Rochester QuadraJet 4bbl Carburetor issue
 
Hello
My truck (1986 GMC Sierra K2500 with 5.7L) have issues with starting, engine will crank but it’ll 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 it’ll not start (it’ll crank, but no start).
Need help
Thanks

geezer#99 05-31-2021 11:23 AM

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?

Captain J 05-31-2021 12:49 PM

Re: Rochester QuadraJet 4bbl Carburetor issue
 
Quote:

Originally Posted by geezer#99 (Post 8926955)
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?

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 didn’t do the rebuild myself, someone else did it.

geezer#99 05-31-2021 01:00 PM

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.

Captain J 05-31-2021 01:14 PM

Re: Rochester QuadraJet 4bbl Carburetor issue
 
Quote:

Originally Posted by geezer#99 (Post 8926990)
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?

geezer#99 05-31-2021 01:18 PM

Re: Rochester QuadraJet 4bbl Carburetor issue
 
Off.
Sometimes easier to use a small flashlight to see inside the carb.

Captain J 05-31-2021 01:45 PM

Re: Rochester QuadraJet 4bbl Carburetor issue
 
Quote:

Originally Posted by geezer#99 (Post 8927000)
Off.
Sometimes easier to use a small flashlight to see inside the carb.

Ok

Captain J 06-01-2021 10:42 AM

Re: Rochester QuadraJet 4bbl Carburetor issue
 
Quote:

Originally Posted by geezer#99 (Post 8927000)
Off.
Sometimes easier to use a small flashlight to see inside the carb.

Update
I’ve 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
I’ll check after few hours.

geezer#99 06-01-2021 10:53 AM

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?

Wgesnerjr 06-01-2021 11:13 AM

Re: Rochester QuadraJet 4bbl Carburetor issue
 
1 Attachment(s)
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.

Captain J 06-01-2021 11:19 AM

Re: Rochester QuadraJet 4bbl Carburetor issue
 
Quote:

Originally Posted by geezer#99 (Post 8927393)
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.

kwmech 06-01-2021 11:21 AM

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

Captain J 06-01-2021 11:21 AM

Re: Rochester QuadraJet 4bbl Carburetor issue
 
Quote:

Originally Posted by Wgesnerjr (Post 8927398)
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.

I’m positive it’s, but I rechecked it aging,

geezer#99 06-01-2021 11:36 AM

Re: Rochester QuadraJet 4bbl Carburetor issue
 
Quote:

Originally Posted by Captain J (Post 8927401)
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?

Captain J 06-01-2021 11:47 AM

Re: Rochester QuadraJet 4bbl Carburetor issue
 
Quote:

Originally Posted by kwmech (Post 8927402)
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

That’s something I’ll do thanks

Captain J 06-01-2021 11:48 AM

Re: Rochester QuadraJet 4bbl Carburetor issue
 
Quote:

Originally Posted by geezer#99 (Post 8927408)
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?

No, it runs fine, subsequent starts are also ok

geezer#99 06-01-2021 12:08 PM

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.

Captain J 06-01-2021 01:17 PM

Re: Rochester QuadraJet 4bbl Carburetor issue
 
Quote:

Originally Posted by geezer#99 (Post 8927427)
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.

Ok, thanks

Captain J 06-01-2021 02:50 PM

Re: Rochester QuadraJet 4bbl Carburetor issue
 
Quote:

Originally Posted by geezer#99 (Post 8927427)
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.

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 they’re 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, 😡😤

geezer#99 06-01-2021 03:43 PM

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.

Captain J 06-02-2021 10:21 AM

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?

geezer#99 06-02-2021 10:32 AM

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?

Captain J 06-02-2021 11:03 AM

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

Captain J 06-02-2021 11:13 AM

Re: Rochester QuadraJet 4bbl Carburetor issue
 
5 Attachment(s)
Pictures

geezer#99 06-02-2021 11:14 AM

Re: Rochester QuadraJet 4bbl Carburetor issue
 
Awesome!
Where in the world do you live?

Captain J 06-02-2021 11:44 AM

Re: Rochester QuadraJet 4bbl Carburetor issue
 
Quote:

Originally Posted by geezer#99 (Post 8927879)
Awesome!
Where in the world do you live?

🤣🤣🤣🤣🤪
I live in a country that temp @6:30 pm is close to 41c?
State of Qatar
However the truck is imported from USA either UT or CO? Among other trucks I own👍🏻

This truck have a loud clunk when in reverse, not sure why?
:gmc2:

geezer#99 06-02-2021 12:09 PM

Re: Rochester QuadraJet 4bbl Carburetor issue
 
A balmy 16C here this morning. Might get to 25C by end of day.

If you have a two piece driveshaft the clunk could be the centre bearing, or a bad u-joint.

geezer#99 06-02-2021 12:38 PM

Re: Rochester QuadraJet 4bbl Carburetor issue
 
1 Attachment(s)
If you’re curious about my location!
I live in a little village by the sea!
On the east coast of Vancouver Island. Province of British Columbia.
About 80 km due west of Vancouver across the water.
Very quiet here except for the sometimes fun of a big bird like this. Injured. Couldn’t fly. Eagle rescue caught her. They’ll fix her up and release her.

The clunk you’re getting.
Is your truck 4 wheel drive?

Captain J 06-02-2021 01:19 PM

Re: Rochester QuadraJet 4bbl Carburetor issue
 
Quote:

Originally Posted by geezer#99 (Post 8927917)
If you’re curious about my location!
I live in a little village by the sea!
On the east coast of Vancouver Island. Province of British Columbia.
About 80 km due west of Vancouver across the water.
Very quiet here except for the sometimes fun of a big bird like this. Injured. Couldn’t fly. Eagle rescue caught her. They’ll fix her up and release her.

Wow, nice place & weather.
Beautiful Eagle, good for you, hope she’ll fly

The clunk you’re getting.
Is your truck 4 wheel drive?

Yes my truck is 4x4 K2500 with auto transmission,

Captain J 06-02-2021 01:36 PM

Re: Rochester QuadraJet 4bbl Carburetor issue
 
Quote:

Originally Posted by geezer#99 (Post 8927905)
A balmy 16C here this morning. Might get to 25C by end of day.

If you have a two piece driveshaft the clunk could be the centre bearing, or a bad u-joint.

It’s one piece, I’ll have to check that

geezer#99 06-02-2021 02:24 PM

Re: Rochester QuadraJet 4bbl Carburetor issue
 
Could be noise from transfer case.
And sometimes bad motor or trans mounts will make a clunk.

Dead Parrot 06-03-2021 10:46 AM

Re: Rochester QuadraJet 4bbl Carburetor issue
 
If it only clunks in 4 wheel drive, suspect the X-fer case or forward drive train.
If it clunks in both 2 & 4 wheel drive, suspect the rear drive train.

Possible that since your idle is fixed, the clunk will largely go away. Even a new drive train has enough slop that switching from D to R or back at high speed can make a noise.

Captain J 06-03-2021 11:10 AM

Re: Rochester QuadraJet 4bbl Carburetor issue
 
Quote:

Originally Posted by Dead Parrot (Post 8928295)
If it only clunks in 4 wheel drive, suspect the X-fer case or forward drive train.
If it clunks in both 2 & 4 wheel drive, suspect the rear drive train.

Possible that since your idle is fixed, the clunk will largely go away. Even a new drive train has enough slop that switching from D to R or back at high speed can make a noise.

It clunks in 2 WD, only in reverse, it been doing this long before the issue with the carb.

geezer#99 06-04-2021 02:23 PM

Re: Rochester QuadraJet 4bbl Carburetor issue
 
Is the carb working better?
Does it start right up like you want?

I’ve installed a torque strap a couple times to limit the motor from moving. Whenever put in gear the motor wants to torque to the passenger side.
I used a short chain with a turnbuckle. Attached to the frame and a convenient bolt down beside the power steering pump.
If the clunk goes away then you know something is hitting somewhere.
If you try that don’t leave the strap in place. Your steering can be effected.

Captain J 06-04-2021 04:03 PM

Re: Rochester QuadraJet 4bbl Carburetor issue
 
Quote:

Originally Posted by geezer#99 (Post 8928711)
Is the carb working better?
Does it start right up like you want?
Carb is fine, it needs fine tuning, engine is shaking little bit
It need depressing the pedal twice to start

I’ve installed a torque strap a couple times to limit the motor from moving. Whenever put in gear the motor wants to torque to the passenger side.
I used a short chain with a turnbuckle. Attached to the frame and a convenient bolt down beside the power steering pump.
If the clunk goes away then you know something is hitting somewhere.
If you try that don’t leave the strap in place. Your steering can be effected.

I’m sure it’s something behind the transfer case to the rear differential,
Im waiting for free time so I can diagnose it probably.
Thank you and the other who helped me to fix the issue. 👋🏻.

The only thing is where to fine a NOS or remanufactered carburetor that fits my truck.
🌺🌹🌷💐

geezer#99 06-04-2021 07:08 PM

Re: Rochester QuadraJet 4bbl Carburetor issue
 
Why are you looking for a nos one or reman carb?
Does your truck start normally now?
You know. Pump it a couple times to set the choke, fire it up, it runs on a high idle, tap the throttle after a couple minutes, it idles down to normal, put it in gear and off you go.

Captain J 06-05-2021 09:40 AM

Re: Rochester QuadraJet 4bbl Carburetor issue
 
Quote:

Originally Posted by geezer#99 (Post 8928776)
Why are you looking for a nos one or reman carb?
Does your truck start normally now?
You know. Pump it a couple times to set the choke, fire it up, it runs on a high idle, tap the throttle after a couple minutes, it idles down to normal, put it in gear and off you go.

It starts but no high or low idle 🤔

I’ve other :gmc2: trucks, one requires a 800cfm carb, one requires 750cfm
Thanks again

geezer#99 06-05-2021 10:58 AM

Re: Rochester QuadraJet 4bbl Carburetor issue
 
I’ve had two Sean Murphy quadrajets. A bit more in price but excellent parts.
And they can restore your original carb for you.
Look around on here.



https://www.smicarburetor.com/

cadillac_al 06-05-2021 12:37 PM

Re: Rochester QuadraJet 4bbl Carburetor issue
 
Those electric choke mechanisms die after a while. That's probably all you need.

geezer#99 06-06-2021 12:56 PM

Re: Rochester QuadraJet 4bbl Carburetor issue
 
Another place for carbs.


https://nationalcarburetors.com/chev...arburetor_1986


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