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DoubleDingo's '81

Discussion in '2wd Pick-Ups C/R 20 2500 C/R 30 3500' started by DoubleDingo, Jul 30, 2012.

  1. Craig 85

    Craig 85 Full Access Member

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    Craig
    Truck Year:
    1985
    Truck Model:
    K30 SRW
    Engine Size:
    454/TH-400/NP205
    My current truck is an early production '85 that used '84 emissions. Standards changed 1/1/85. I know CA HD trucks then had 2 smog pumps and the stainless exhaust manifolds. I remember seeing the tail pipes on half tons too. I always thought it was to slow down the pellets coming out of the pancake cats as they failed. Trucks are the only GM vehicles that had side exhaust at this height. I also remember the same tips on a friend's 79 or 80 C10 diesel. I can't recall if it had the screens or not. This was back in the late 80's.

    I figured they just used the same tail pipes in HD trucks due to cost.
     
  2. DoubleDingo

    DoubleDingo When In Doubt, Throttle Out

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    Bagoomba
    Truck Year:
    1981, 1965
    Truck Model:
    81-C20 Silverado Camper Special-TH400-4.10s; 65-C20 with 4:57 gears and Borg Warner Overdrive
    Engine Size:
    Carb'ed Vortec 350; 1972 L48 350
    Mine is an early '81, the guy at the muffler shop was surprised to see there was no o2 bung, no cat, etc. It's always interesting to see what the car manufacturers did as emissions and fuel economy tightened up.
     
  3. HotRodPC

    HotRodPC Administrator Staff Member

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    HotRod
    Truck Year:
    85 K20 LWB / 86 K5
    Truck Model:
    Silverado / Silverado
    Engine Size:
    454 - Turbo 400 - 3.73 350 - 700R4 - 4.10
    In the early squares I think Th350 was in the 3/4 tons up to 76 or 77 behind 350's. Not positive on the year, but for a fact in the 80's the 3/4 tons got Th400s even with 350's and I want to say even with I6 and V6's.
     
  4. DoubleDingo

    DoubleDingo When In Doubt, Throttle Out

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    Truck Year:
    1981, 1965
    Truck Model:
    81-C20 Silverado Camper Special-TH400-4.10s; 65-C20 with 4:57 gears and Borg Warner Overdrive
    Engine Size:
    Carb'ed Vortec 350; 1972 L48 350
    I've always been a fan of the TH400. That and the SM420. Mainly because those are what I had to run in my vehicles, but also because of their durability and reliability. The Saginaw 4 speeds weren't bad either.
     
  5. bucket

    bucket Super Moderator Staff Member

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    Truck Model:
    K5 thru K30
    Engine Size:
    350-454
    It must be a California thing I guess, I've never seen them here. My Burb also had the stainless manifolds and dual smog pumps. But just standard tailpipes and they were most certainly the factory original pipes too.

    Were the screens right at the very end of the pipe?
     
  6. DoubleDingo

    DoubleDingo When In Doubt, Throttle Out

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    Truck Year:
    1981, 1965
    Truck Model:
    81-C20 Silverado Camper Special-TH400-4.10s; 65-C20 with 4:57 gears and Borg Warner Overdrive
    Engine Size:
    Carb'ed Vortec 350; 1972 L48 350
    Yeah, the screen if I recall was maybe half inch in from the end. Mine had a hole punched in it for an emissions sniffer when testing needed to be done.
     
  7. Craig 85

    Craig 85 Full Access Member

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    Truck Year:
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    Truck Model:
    K30 SRW
    Engine Size:
    454/TH-400/NP205
    About 2" from the mouth of the pipe.
     
  8. DoubleDingo

    DoubleDingo When In Doubt, Throttle Out

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    First Name:
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    Truck Year:
    1981, 1965
    Truck Model:
    81-C20 Silverado Camper Special-TH400-4.10s; 65-C20 with 4:57 gears and Borg Warner Overdrive
    Engine Size:
    Carb'ed Vortec 350; 1972 L48 350
    Lately the truck wouldn't settle down unless I tapped throttle and then it the idle would drop. After it was good and warm it would, but this time of year that can take a while, and with it having vortec heads and vortec quadrajet intake, which doesn't have a heat cross-over, it takes a long time for the carb to heat up too, even with warm air coming in from the heat stove. Back in 2001 I got a q-jet from my brother when he wrecked his '85 3/4 ton in 2001. I put it on my '65 but it never ran right, and when I mentioned it to Pop he said it's because I had all but one port plugged on the thing. So I took it off but never tossed it, it sat in the back shed. The carb on the '81 needed to be rebuilt, but I remembered that old one in the back shed. I got a kit from Cliff Ruggles for the vortec setup, rebuilt it, but when I went to install it back 2014 I noticed it is a little different, and I didn't have the resources to use it at the time. So I got basically the same kit from Cliff for the carb in the '81 but I was afraid to do the throttle shaft bushings. It ran great and since installing it in 2014 I haven't had to touch it. Well, the throttle shaft is pretty slpppy now and I suspect that is what caused the higher idle until the pedal was tapped. Odd it would settle back down when it was good and hot, though. A year or two ago I later found a stud that I could bolt onto the '85 q-jet for throttle cable, and put it in the "carb parts tote".

    There's the back story, so on Saturday I dug out the '85 q-jet, swapped it on the truck, and it fired right up. Great. But it, too, idled high. Hmmm. Nothing I did would get the idle to drop, not even tapping the throttle like the other carb. Got out the timing light and the timing was way advanced. I suspect the other carb, with it the massive air leak from the loose throttle shaft was allowing the timing to drop enough to run normal. Adjusted the timing to 10* BTDC and the idle settled down. Plugged in the vacuum advance hose and it jumped up again. I always forget that this truck prefers to have the timing adjusted with everything hooked up. So I installed the air filter assembly, hooked up all the vacuum lines, adjusted the timing and it purrs like a kitten now.

    However, there is something new that didn't happen before. When I let off the throttle it pops out the exhaust. I looked it up and the reason is typically on high-flow exhaust systems there is unburned fuel in the exhaust that gets ignited when you let off the throttle. But why now? It never did it before? Everything is hooked up from the old carb including the throttle lever actuator. I forgot about it and this morning it sounded like three gun shots went off. Oops. I'll need to remember to ease off the throttle until I can get this resolved. Don't need to be shot by a gang member or the police.
     
    Last edited: Apr 13, 2020
  9. Craig 85

    Craig 85 Full Access Member

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    Truck Year:
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    Truck Model:
    K30 SRW
    Engine Size:
    454/TH-400/NP205
    EDIT: Does your truck have this throttle lever actuator set up or the A/C set up? Mine has it, but it's a 454. It's supposed to work on deceleration between 1500-2000 RPM to stop the back fire. I'm not sure the 350's with HD emissions had this. I know my 1/2 ton 350 had the actuator for the A/C, but serves a totally different purpose.

    Throttle lever actuator 2.jpg TSC 2.JPG
     
  10. DoubleDingo

    DoubleDingo When In Doubt, Throttle Out

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    Truck Year:
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    Truck Model:
    81-C20 Silverado Camper Special-TH400-4.10s; 65-C20 with 4:57 gears and Borg Warner Overdrive
    Engine Size:
    Carb'ed Vortec 350; 1972 L48 350
    It has it. I mentioned it in my post but not by its actual name. I'll check to see if it's working, it worked on the old carb.
     
  11. DoubleDingo

    DoubleDingo When In Doubt, Throttle Out

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    Truck Year:
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    81-C20 Silverado Camper Special-TH400-4.10s; 65-C20 with 4:57 gears and Borg Warner Overdrive
    Engine Size:
    Carb'ed Vortec 350; 1972 L48 350
    It's curious because none of my carbed vehicles without the throttle lever actuator back fire upon deceleration
     
    Last edited: Apr 13, 2020
  12. DoubleDingo

    DoubleDingo When In Doubt, Throttle Out

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    Truck Year:
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    Truck Model:
    81-C20 Silverado Camper Special-TH400-4.10s; 65-C20 with 4:57 gears and Borg Warner Overdrive
    Engine Size:
    Carb'ed Vortec 350; 1972 L48 350
    @Craig 85 can you do me a favor and show me which port yours is hooked up to and the vacuum hose routing? Supposedly my truck is an oddball as any time I look up stuff for it the results want to default to 454. The engine is the factory engine, 350 with the partial VIN. But it may have the 454 emissions for the C20 as I was told in '81 Chevy had something like eight different stickers for the air cleaner assemblies. Since the carb I put on is for an '85, perhaps using the routing from your CA emissions truck may work for this. If it doesn't I may just have to break down and just do a full rebuild on my '81 carb or buy one.
     
    Last edited: Apr 13, 2020
  13. DoubleDingo

    DoubleDingo When In Doubt, Throttle Out

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    Truck Year:
    1981, 1965
    Truck Model:
    81-C20 Silverado Camper Special-TH400-4.10s; 65-C20 with 4:57 gears and Borg Warner Overdrive
    Engine Size:
    Carb'ed Vortec 350; 1972 L48 350
    On the '81 carb the port that the torx driver is sitting on,

    20200413_173323.jpg

    Was where the torx driver is pointing to here,

    20200413_173400.jpg

    Both on the bottom so I assumed full vacuum. Nope, the port in the first photo is ported or completely plugged as it has no vacuum at idle. Didn't rev it, didn't think about that until just now.

    Does the throttle lever actuator need full vacuum? The port that is to the right and above the torx in second photo is the same spot the actuator was connected to on the '81 carb.

    Did GM move ports around? I know each carb is pretty much application-specific but I figured the ports might be the same for the most part.

    It does pull a nice steady vacuum though....

    20200413_173519.jpg
     
  14. Craig 85

    Craig 85 Full Access Member

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    Truck Year:
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    Truck Model:
    K30 SRW
    Engine Size:
    454/TH-400/NP205
    Here's my emissions routing. My truck is an early '85, but it has OEM 1984 emissions. The Throttle Lever Act. hooks up to the TRC Valve. That then splits between the bottom right of the carb and the smog pump. The TRC Valve has brown and yellow wires running to it.

    It's dark out, so I can get some photos tomorrow if you need them.

    IMG_1360.JPG IMG_1434 (2).jpg
     
  15. Craig 85

    Craig 85 Full Access Member

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    Truck Year:
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    Truck Model:
    K30 SRW
    Engine Size:
    454/TH-400/NP205

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