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FINALLY: Swapped my 305 for a 350!!

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Eric, Jan 28, 2001.

  1. Eric

    Eric Registered Member

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    Just did the deed, took a little over 2 days to finish. She runs GREAT! Much smoother and more power than my sluggish 305.

    Got some questions though:
    1) The engine is running a little warm, aound 210. I have a new water pump and thermostat. Creaps up to 210 when going up hills or at high speeds otherwise sits right at 195. Is it possible that my rochester is running lean with 305 jets? Any advice?

    2) My vacuum is around 18in Hg at idle, is this correct. I thought I should be getting closer to 21?

    3) Getting a slight stumble when accelerating from a standstill, otherwise the motor pulls clean with no trouble. The enigine has been timed and tuned. Could this be accelerator pump in the carb (again 305 to 350)?

    Thanks for any help!

    One eyed super fly- watch out!
    86 K5 Blazer
     
  2. If its a new or rebuilt motor it mite take a little time to break in.On the carb issue,the 305 uses the same q jet as a 454 so it should be fine.You mite need a new one or a rebuild though,if you have a little stumble its prob the accelerator pump.The other prob with older carbs is they develope leaks where the trottle shaft goes into the base of the carb,if this is the case then you need to have new bushings installed at this point.Check for leaks there.Good luck
     
  3. Bone85K5

    Bone85K5 1/2 ton status

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    Did the same thing about this time last year. Its a real noticable difference.. Good luck with tuning out the little bugs, you'll love the new found power.

    Ben
    www.BenjaminBone.coloradoK5.com
     
  4. Thunder

    Thunder 3/4 ton status

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    The symptoms you describe sound to me like the carb may be a little to lean This could come from Too small of jets, Leaking throttle shafts, or a vacume leak. If you are getting 18 hg at idle and the needle on the guage aint jumping around the vacume should be ok. I would try bigger jets.
     
  5. HarryH3

    HarryH3 1 ton status Author

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    Vacuum readings are affected by altitude. The higher you get, the lower they will read. Can't tell where you are, since your profile isn't filled out. Here in Colorado Springs, the readings are well below what is standard for sea level.

    <font color=black>HarryH3 - '75 K5</font color=black>
    <A target="_blank" HREF=http://ThunderTruck.ColoradoK5.com>http://ThunderTruck.ColoradoK5.com</A>
     
  6. TPI86

    TPI86 1/2 ton status

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    I did the same, replaced 305 with 350 and used stock carb Q-jet, ran so lean started to burn the cats and the rubber off the hangers. Had to richen it up a little.

    Add some more power to the beast [​IMG] try fuel injenction. just added a 86 TPI system, excellant throttle response, costs some cash, but well worth it.
     
  7. Eric

    Eric Registered Member

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    The vacuum guage holds steady, so I am thinking it is not a vacuum leak. My mixture screws are sealed so I can't tune while in the idle circuit either. Has anyone ever drilled these out and tried to tune or would I be opening up a hole new can of problems.

    I will probably get a q-jet rebuild book and change out the accelerator pump and jets with something which gives a little more gas. Anyone know the jet size I will need and if not should I just creep up to the next size?

    Thanks everyone for the help...

    One eyed super fly- watch out!
    86 K5 Blazer
     

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