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carb issues

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by 76_gmc, Mar 21, 2007.

  1. 76_gmc

    76_gmc Registered Member

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    When i bought this 84 K5, the guy said it was a crate 350, with roller rockers??? anyway, it sputters at times and i get an occassional backfire, but more of a misfire and you can really smell the fumes then. It has a 600 cfm edelbrock carb (which i know sucks, but thats what it has). Maybe the carb is too small. but will that cause it to sputter and misfire???

    i have timing light, at idle its alittle above 12. is that good?
     
  2. dyeager535

    dyeager535 1 ton status Premium Member

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    12 is fairly high, try 8 or so. Play with timing, you might be surprised how much that affects how it runs.
     
  3. W7NB

    W7NB 1/2 ton status

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    Having a carb with a flow rate less then optimal (too small) would not create an over rich condition with the gas smell you describe, but instead would lean out at higher rpms and create ping (spark knock).

    What do the plugs look like? Wet? Oil fouled? Carboned up?

    Also, are they the corect plugs for the motor? I have seen several instances when people had a pre emisson truck with a post emission crate motor and just went to the parts store and bought the same plugs as the old engine had. Make sure the heat range and gap match the motor and dizzy you are using now. Also check the plug wires and as suggested the timing.

    I would also check the fuel pressure into the carb. Aftermarket performance fuel pumps may have higher then stock fuel pressure and simply be blowing fuel past the float seats. A simple in line regulator will rectify that.

    I would also check the float levels. I have seen way too many carbs rebuilt or replaced simply because the float levels were off or due to elecrical system problems.
     
  4. 76_gmc

    76_gmc Registered Member

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    Last night I took off the carb, I am retarded in describing somethings, as I am new at this but here it goes...

    the linkage on the right side (looking at the front of it) and rear is rather loose and worn, I believe this is what opens the other two barrels at the right input. The left front vac line went to the manifold, where it was T-boned to the transmission. The middle is to the PCV and the right was plugged. The vac line in the middle rear was a kinked solid tubing to the brakes. It has a Mallory fuel and ignition system.

    I bought this truck 3 weeks ago and know very little, just that i like it and I ain't getting any younger for toys.

    What plugs do you recommmend? And gaps? I will pull the number one plug and see what she looks like. I really don't want to tear her open, I don't have any replacement gaskets, but if i have to, I will and check the floats.

    What I really want to do is get a 750 Holley....one day.

    thanks for the help.
     
  5. 76_gmc

    76_gmc Registered Member

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    this morning i finished putting all back, replacing all the vac lines and put in a fuel psi gauge. my pump will put out between 6-9 psi for a few seconds and then quit, 0 psi for while and then pump again.

    new pump?
    filter??

    but its good to narrow this down.
     
  6. W7NB

    W7NB 1/2 ton status

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    That fits what I expected. When the PO did the crate motor swap he put in an aftermarket ignition and fuel pump. Probably an Edelbrock intake manifold as well.

    Don't pull just the number 1 plug, but pull several and see how they look. From your description your running over rich so it can be either too much fuel or poor burn due to ignition issues. I can't reccomend a plug and gap, but if you post up the exact combo (HEI or stock coil, engine head info etc) perhaps others can.

    And if your going to spend the money on a Holley, why not buy an aftermarket TBI setup?
     
  7. 76_gmc

    76_gmc Registered Member

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    this is just puzzling...
    i replaced the fuel pump...runs for a bit and then 0 psi...can feel the pump working, but zero psi. i bypassed the inline regulator...still the same issues.

    what else???
     
  8. kirkallen143

    kirkallen143 Registered Member

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    Make sure you have a proper ground for the fuel pump, you never did say if it was electric or not, but by what you are describing it sounds like you have an electric pump. If I am wrong and this is a mech. pump, then you have a worn cam where the mech. pump arm resides.
    Now if it is electric, the pump needs to be close to the tank as you can get it, they are better pushers that pullers, with fuel that is. Do you have/is there a relay installed for the pump? Long wire runs will not provide the voltage necessary to run the pump.
    Let us know.

    Kirk
     
  9. 76_gmc

    76_gmc Registered Member

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    I have an electric pump, mounted under the hood. First, was the Mallory 110 series. it would pump great for 30-45 mins then nothing. so i bought a cheap guy...installed and same thing. i can feel the pump is on...today i am going to crack lines to see what else i can give ya. if i am suppose to install her near the tank...where?????
     
  10. kirkallen143

    kirkallen143 Registered Member

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    I have mine installed on the frame rail about a foot away from the tank. You can use some self drilling screws to mount it, and I advise you to put some type of rubber/insulator under it when mounted.

    Being mounted that far back you will need a relay so you do not get voltage drop at the pump and it will perform like it should.

    I have mine on a toggle switch directly from the battery and then the regular voltage source is from the ignition switch, easy enough.

    Kirk
     
  11. 76_gmc

    76_gmc Registered Member

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    i bought a mech pump and when the mount plate comes in, i will install it. if that works, one day down the line i will remount as you said near the tank an elec pump. should have the plate this week and will let you know if this problem goes away. thanks for the help
     
  12. kirkallen143

    kirkallen143 Registered Member

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    Anytime, good luck.

    Kirk
     
  13. Thunder

    Thunder 3/4 ton status

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    FYI. You have to mount an electric FP at the same level or lower than the bottom of the fuel tank. The closer to the tank along the frame the better.
    Electric pumps are not designed to fight gravity and pull gas out of your tank they are just pushers they need unobstructed gravity flow into them from the tank to work right. They can pull gas for a short time to prime themselvs but if they are forced to pull for a long peroid of time they overheat and shut off.
    Also a 600 CFM carb is about perfict for a stock or mild build 350
     
  14. 76_gmc

    76_gmc Registered Member

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    put in the mech pump and that was it. now one day i will mount an elec pump in the right spot. one question, can you have an in-line reg with a mech pump?
     
  15. kirkallen143

    kirkallen143 Registered Member

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  16. MrArmyAnt

    MrArmyAnt 1/2 ton status

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    I had a remanufactured crate installed in my 77, how can i tell if it is post emiisions? That might be my problem...
     

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