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Carburetors Carb discussion and questions. Upgrading your Third Gen's carburetor, swapping TBI to carburetor, or TPI to carburetor? Need LG4 or H.O. info? Post it here.

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Old 03-01-2006, 01:05 AM   #1
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Join Date: Dec 2005
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Car: 78 Datsun 280z with GM 350
Engine: Carbed TBI (Truck) 350 W/Ported 193s
Transmission: 700r4
Axle/Gears: Stock 280Z Rear

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What did I do wrong with my carb rebuild.

I rebuilt a Qjet carb here recently. And tested it for the first time on the car today. It revved real good. And I loved the way it "felt" on the motor.

But twice it got hung up and stayed revved. Once while In drive. The motor was still pushing with my front tires locked up in braking at a stop sign. All outside linckage was fine, I could see nothing on the outside of the carb that would make the throttle stick open. And as far as I could tell, The throttle blades were closing all the way. Looking into the top of the carb, the rear blutterflies were closed all the way too. Any ideas?

I had the holley in the back seat, changed it out at the stop sign, and went on about my buisiness.
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Old 03-01-2006, 01:08 AM   #2
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Must have been a long stoplight?
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Old 03-01-2006, 08:08 AM   #3
naf
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Location: Lexington, SC
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Car: 1987 SC/1985 TA
Engine: 350/vortec/ccc q-jet
Transmission: 700-R4
Axle/Gears: 3.27 9-bolt

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Choke or choke linkage sticking, choke wire loose, no power or not connected (was choke open completely when this occured?), vaccuum leak, throttle return spring weak, throttle linkage binding.

I'd look at the choke first.
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Old 03-01-2006, 11:40 AM   #4
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Car: 78 Datsun 280z with GM 350
Engine: Carbed TBI (Truck) 350 W/Ported 193s
Transmission: 700r4
Axle/Gears: Stock 280Z Rear

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It was a stop sign, so there was no time limit. It took less than 5 minutes for the two of us to change carbs.

I left the choke off, as I dont intened to use one. Is this it? Is there some internal mechanism the choke controls that, if left off, could cause that to happen?
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Old 03-01-2006, 11:54 AM   #5
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I would also think choke. How high was it trying to rev?

And by 'left off' do you mean you just took the plate off, or did you remove the fast idle cam and all the associated linkages beside the thermostat?
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Old 03-01-2006, 12:13 PM   #6
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Car: 1987 SC/1985 TA
Engine: 350/vortec/ccc q-jet
Transmission: 700-R4
Axle/Gears: 3.27 9-bolt

Classifieds Rating: (4)
Fast idle cam could be hanging loose and randomly engaging?
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Old 03-01-2006, 03:32 PM   #7
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Car: 78 Datsun 280z with GM 350
Engine: Carbed TBI (Truck) 350 W/Ported 193s
Transmission: 700r4
Axle/Gears: Stock 280Z Rear

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I left off all the stuff on that side of the carb, choke and fast idle cam. I plugged the associated vacuum lines.

I'd say it hit 3500-4500 rpm. I don't have a tach.

Fast idle cam hanging loose and randomly engaging? That sounds good, give me more info...
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Old 03-01-2006, 03:46 PM   #8
naf
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Join Date: May 2004
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Car: 1987 SC/1985 TA
Engine: 350/vortec/ccc q-jet
Transmission: 700-R4
Axle/Gears: 3.27 9-bolt

Classifieds Rating: (4)
If you've taken everything off, there should be nothing left to hang up. Take a photo of whats left and post it if you can.

May want to take a photo of the throttle linkage side too. Chance of a hang up there?
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Old 03-02-2006, 12:05 AM   #9
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Car: 78 Datsun 280z with GM 350
Engine: Carbed TBI (Truck) 350 W/Ported 193s
Transmission: 700r4
Axle/Gears: Stock 280Z Rear

Classifieds Rating: (0)
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Last edited by Tony78_280z; 03-02-2006 at 12:14 AM.
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Old 03-02-2006, 12:12 AM   #10
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hmm, those images are hosted by angelfire alright...
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Old 03-02-2006, 12:14 AM   #11
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Car: 78 Datsun 280z with GM 350
Engine: Carbed TBI (Truck) 350 W/Ported 193s
Transmission: 700r4
Axle/Gears: Stock 280Z Rear

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Sorry again, modified links.
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Old 03-02-2006, 07:42 AM   #12
naf
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Car: 1987 SC/1985 TA
Engine: 350/vortec/ccc q-jet
Transmission: 700-R4
Axle/Gears: 3.27 9-bolt

Classifieds Rating: (4)
Everything looks clean. My guess would be throttle cable bind or weak return springs? Maybe Sonix will chime in with an idea.
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Old 03-02-2006, 12:03 PM   #13
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Also check throttle body to main body gasket alignment.
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Old 03-02-2006, 12:03 PM
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