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Running like crap, just dont get it

Discussion in 'The Garage' started by MattK, Jan 28, 2007.

  1. MattK

    MattK 1/2 ton status

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    400 sbc, quadrajet carb

    it runs the worst when it's below like 50* degrees outside. from a cold start it smokes and sputters for a good half hour before it finally gets warm.

    most of the time it's fine after it gets warm. it'll idle pretty smooth, just a little high and have a small amount of smoke still (no much whitish/bluish smoke). sometimes though it will be at operating temp going down the road and it sounds like im losing a cylinder or more.

    im not afraid to tear into this or throw parts at it, but i really have no clue when it comes to these carbs.

    help!
     
  2. MattK

    MattK 1/2 ton status

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    Replaced spark plug wires. That helped some. Still getting that odd cutting out at speed.
     
  3. Craig Artzner

    Craig Artzner 3/4 ton status GMOTM Winner

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    My truck sputters a bit at idle when it's below 40 until it gets warm. It has an open air filter. I'm currently restoring a stock air cleaner with a heated air actuator. But I still need to figure out what to do for a heat stove since I have headers. Guess I'll have to build one...

    Are you running heated inlet air or a stock air cleaner on your truck? If you have an open air filter, just replacing it with a stock enclosed one will help your truck run better when cold, even without the heated inlet air...then you can put the open one back on when the weather gets warm again.
     
  4. koldsimer

    koldsimer 1/2 ton status GMOTM Winner

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    After seeing the way your truck was running, i'm thinking it just needs a good cleaning. Your truck sat for quite a while in the past few months and I bet it's just gummed up. It seems like your float is sticking causing it to flood out. Of course, my extent of carb knowledge is extremely limited. When I had enough of my either on or off carb I just went to O'Reilly's and got a $200 rebuilt one. One of the best $200 i've ever spent.:wink1:
     
  5. MattK

    MattK 1/2 ton status

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    yeah i gotcha. im runnin the stock type setup with the heated air circulator you're talking about. i've got headers too, it looks like someone simply tacked a 2" long pipe to the header for the foil tube to attach to. pretty simple. i think it's a bit more serious than that though cuz it just about wont run. it took about 30 min of idling to get up to temp today and it was only about 40*.:doah:

    yeah i gotcha. my grandpa said he had heard it running in the driveway the other day and he said it sounded as if i was gettin too much fuel because of the float sticking as well. steven is gonna help me check it out tomorrow and hopefully get it fixed. ive got some wheeling to do dammit! haha
     
  6. koldsimer

    koldsimer 1/2 ton status GMOTM Winner

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    I was just thinking- the way it was running right when you started it after it sat for a few minutes would indicate it was flooding while just sitting there. Try running a bottle of fuel system cleaner and see if it helps before you go tearing it apart.

    I don't see how you can stand to not be out there spinning your brand new boggers! The dude that was riding in my truck didn't have much to say... I think he may have been a little skeered.
     
  7. MattK

    MattK 1/2 ton status

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    Yeah I may try that too man. LOL I bet you had that guy at least a little scared hahahaha.
     
  8. diesel4me

    diesel4me 1 ton status Premium Member

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    water in the fuel??..

    Sounds like either water is in your gas,or possibly the carb is icing up--its highly possible for it to frost up even if temps are 50 degrees!..I had no end of carb icing troubles with my Edelbrock Performer carbs I had on my SB 400,and other vehicles..up here its foggy and damp a lot,and days like that were pure misery to drive my trucks in..they would stall every time I let off the gas,or choke up and run rich as hell,until the carb finally got warm enough,which took a half hour in some cases,some days it NEVER warmed up enough!..

    Having a carb spacer or adapter amplifies this problem,they insulate the carb from heat,when you WANT it to heat up!..some vehicles used a spacer with hot water passages in them, so the coolant would pre-heat the air fuel mix for proper combustion..cold intake air is great for maximum HP at the dragstrip in July,but sucks when its below 50 degrees!..the carb's venturies will frost up and clog with ice,and make the carb run rich due to blocked air vent tubes,etc..

    I "fudged" a fix on my 79 C-10 by plugging the EFE Valve (heat riser) dewhicky to manifold vacuum,so the butterfly in the heat riser stayed closed all the time--it made a world of difference!..on days warm enough for it to run normally I'd just put the vacuum hose back in its stock location on the PVS switch in the thermostat housing..the heat riser directs exhaust gasses under the intake underneath the carb,and its is a needed item for the fuel to vaporize properly..

    My 400 SB had no heat riser,so I had to use a stock air cleaner and add a "stove" to the exhaust manifold,the OEM one rotted off decades before...adding a few cans of Isopropanol Dry Gas helped immensely,but got expensive fast..if you add a few bottles and your troubles go away,I bet its carb icing or water in the gas thats causing your truck to run crappy...:crazy:
     
  9. MattK

    MattK 1/2 ton status

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    good info! about the water in the gas...what causes that? is it an incidental type condition or is there something that would cause me to constantly develop water in the gas?
     
  10. diesel4me

    diesel4me 1 ton status Premium Member

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    many sources..

    Water can condense in the gas tank,or your gas station's tanks might be tainted ,and they are selling you water AND gas...I've seen one truck come in my friends shop that had a rotted out filler neck,and the tires flung water,mud,and leaves into the gas tank!..it only takes a little to screw up the way it runs too..:crazy:
     
  11. goldwing2000

    goldwing2000 Guest

    Maybe I missed something but did you verify that the choke is set and operating properly?

    What about the t-stat?

    I ran a 400SB with a Holley (early) and a Q-jet (later) all year long in Michigan, both with an open-element filter and no heat riser, and never had any icing problems.
     
  12. MattK

    MattK 1/2 ton status

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    not sure on the choke. when cold it's just about shut, that's about all i can tell you. i have roe's qjet book on the way. my searching couldn't find anything online that could dumb is down enough for me.
     
  13. goldwing2000

    goldwing2000 Guest

    Roe's book is good. Set the choke as soon as you get it and go from there.

    Are you running an electric or a hot air choke? If hot air, married or divorced (the choke, not you :D )? Is it opening fully as it warms up?
     

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