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Q-jet jetting opinions

Discussion in 'The Garage' started by mrk5, Nov 8, 2004.

  1. mrk5

    mrk5 The Sticker Guy Moderator Vendor GMOTM Winner Author

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    I've got some questions about jetting.

    The carb is one I bought from a fellow member living in California. It was built by Jet Performance.

    I think the primary jets are good. The truck doesn't surge at cruising speed. Don't know how to tell if I'm too rich though, but I think it is okay.

    When I put the pedal to the floor, that is when I have problems. The carb seems to bog. I kinda sounds like it is cutting out, and power really drops. It starts to get a little better as the rpm gets above 3000, but still not great.

    I think I need to go down in rod size. I've also heard that the hangar might need changed also.

    Does it sound like I'm on the right track?

    Also any possible recommendations for the correct rods & hangar at my elevation (~5000ft). Just looking for a decent starting place.
     
  2. rcamacho

    rcamacho 1/2 ton status

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    Sounds like the secondaries are kicking in too soon.
     
  3. dyeager535

    dyeager535 1 ton status Premium Member

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    If it's bogging while you are trying to accelerate, more than likely you've got a timing, accelerator pump, or secondary issue.

    I've been able to solve a bog off idle with some mild timing changes. You can also adjust how fast or how slow the secondaries open up on the passenger side upper air valve shaft. Accelerator pump isn't much to fix on it, either it works or it doesn't, although there is likely some tuning points of it I'm not aware of.

    Secondary adjustments (ease of opening, rods and hangars) make a HUGE amount of difference though, and are fairly easy to play with. Even if you don't have the rods or hangars laying around to play with, the tension on the seconadry air valve is easy enough to play with.
     
  4. mrk5

    mrk5 The Sticker Guy Moderator Vendor GMOTM Winner Author

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    It's not an off idle bog.

    It does this when I'm cruising down the highway and I put the pedal to the floor. As long as I don't depress the pedal more than about halfway, it's fine. As soon as I accelerate enough to get where I believe the secondaries are opening, it starts to bog. No problems with acceleration below that half throttle region.

    Is the secondary air valve spring adjustment the one that requires two wrenches, one for a lock screw and the other for the adjusting screw.
     
  5. dyeager535

    dyeager535 1 ton status Premium Member

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    Gotcha.

    Yes, secondary adjustment is the flat blade/allen key adjustment on the PS.
     
  6. rhuarc31

    rhuarc31 Registered Member

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    Sounds like the secondary air valve opening too early, a very common problem with JET carbs. Jet tends to set the spring tension at the absolute minimum. Having said that I've had to repair several carbs straight from JET because the spring for the air valve wasn't hooked up or was broken. On a side note, I was not impressed with their "stage 3" carb. Pick up the book Rochester quadrajets by Doug Roe and you'll be able to do far more than they do.
     
  7. mrk5

    mrk5 The Sticker Guy Moderator Vendor GMOTM Winner Author

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    Thanks for the replies.

    I've been thinking about adjusting the air valve, but I didn't know how common it was for that to need adjusting. Thanks, rhuarc31; you made up my mind on that.
     

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