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truck stumbles

Discussion in 'The Garage' started by bigbadchev84, Jun 21, 2006.

  1. bigbadchev84

    bigbadchev84 1/2 ton status

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    i drove my 78' ford for the first time in a couple months it has a 400m with an edelbrock carb, its got a lopey cam in it and at a stoplight today and everyothertime im stopped and start to go it studders almost dies then goes, if you ease into it it does just fine. where should i start to look?

    and no its a ford jokes please, im trying to sell it:D
     
  2. nstarry

    nstarry 1/2 ton status

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    seafoam is where I would start !
     
  3. 454k30

    454k30 1/2 ton status GMOTM Winner

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    I had a very similar problem with my edelbrock carb. What fixed it for me, after many frustrating needle and jet changes, were the step up springs. I changed from the stock springs to ones rated and 2" higher and that annoying stumble went away. These carbs came with 5"Hg springs, I put in the 7"Hg. I have to assume that my engine had to much vacuum for the springs that were in there and was causing a serious lean condition. It takes off from lights now like it meens it. the springs I got were in a kit with several different spring options. Just make sure you use two of the same colored spring! Give it a try and see if it helps. I think they are less than $10 and available at Kragen.
     
  4. bigbadchev84

    bigbadchev84 1/2 ton status

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    how do i adjust the front screws to fatten it up a little?
     
  5. diesel4me

    diesel4me 1 ton status Premium Member

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    mixture screws

    Turning the idle mixture screws out (counter-clockwise) will richen the IDLE mixture,but has little to no effect past idle..changing the jets and metering rods is the only way to adjust the mixture for anything above idle...

    If you have a Performer carb,the accelerator pump has 3 holes in its linkage...changing the stroke by putting the linkage in one of the other holes might help---it could be the accelerator pump itself is worn, and not squirting a good shot in on fast acceleration...but I'd look very closely for vacuum leaks,using carb cleaner sprayed on suspect areas,and check the timing first..both of them cause 90% of stumbling and poor idle complaints,not the carb itself..:crazy: ..
     
  6. theperfectgarage

    theperfectgarage 1/2 ton status

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    I'm with Diesel 4 me, start with the pump shot linkage, then the step up springs. But my question is, did it stumble like this before you parked it? The carb didnt un - adjust it's self if you get my drift. I could see the accel. pump drying out and failing, there about 8 bucks. Any vacuum leaks ?
     
  7. diesel4me

    diesel4me 1 ton status Premium Member

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    good point...

    Yes,a good douching with carb cleaner might free up the metering rods if they are gummed up with stale fuel from sitting..might just be old stale gas, or water in the fuel to blame too..and sitting kills accelerator pumps,especially if the carb evaporated all the fuel out of the bowls while it sat...did the gas pedal feel "stiff" the first few times you pumped it??--if so,I bet the accelerator pump "cup" was damaged,and now isn't squirting enough gas in when you accelerate...

    I've noticed on my truck,and a few other chevy V8's with an Edelbrock Performer,hooking the vacuum advance hose to the manifold vacuum port,rather than the usual "ported" vacuum port GM usually used,makes the motor idle smoother,a bit faster,and it eliminated a slight hesitation it had on takeoffs...I swear the gas mileage improved a bit too,probably due to more advance at idle..and it no longer "pings" under a load on the highway like it did on "ported" vacuum...maybe it'll help a Ford too...:crazy:
     
  8. 1985_K5_Silverado

    1985_K5_Silverado 1/2 ton status

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    Sounds a lot like you need stiffer step-up springs to get the metering rods lifting at lower vacuum. They factory-install lighter springs for "fuel economy", and they're usually not stiff enough to get those rods up right when you punch it.
     
  9. bigbadchev84

    bigbadchev84 1/2 ton status

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    thanks for the help, but i never gotta chance to mess with it, a buddy called me up about it and now its gone:D it was a sharp looking truck for a ford, but now that the space is free in the driveway i get to get the ole chevy insured and back to dd use for now, ive been driving my 05' taco, but miss the sound of the 39.5 boggers humming down the road:D
     

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