Q850 idle tuning help needed

Discussion in 'Other' started by deluxe68, Aug 8, 2015.

  1. sailbrd

    sailbrd Well-Known Member

    Sound like you are doing a good job. Would not hurt to try bigger air bleeds but not necessary. I went up a couple of steps on air bleeds and idle screws went from 3/4 out to 1 turn out. Idle went from good to better. Not a lot better.
  2. deluxe68

    deluxe68 Well-Known Member

    Is there any advantage to changing the stock needle & seat from a .120 to a .110 ?
    I have read that the .120V is usually used for up to 800 hp and the .110V is for up to 650hp both at 7psi for gasoline.

    I'm running a mechanical fuel pump with no regulator, should I not be using the .110V or smaller N&S ?

  3. deluxe68

    deluxe68 Well-Known Member

    I'm not sure if there is an advantage or not but, I put the .110's in today to try out and they seem to work fine.
    So I guess the only thing that it changed was how fast the bowls fill. Correct?

  4. deluxe68

    deluxe68 Well-Known Member

    The Q850 is doing pretty well now, I have made some more changes for the better unless it's the cooler weather.

    IFR's are .032 / Pri jetting is 73 / Sec jetting is 79 (blocked PV)
    IAB's are .074 / HSB are .033 (stock) / 30cc pumps (stock) / Squirters are 31 / PV is 5hg
    Pink cams front and rear (may put the red back on primary side, it's a little faster)

    Running 13hg idle vacuum in gear at 825 +/- rpm and 875 +/- rpm in park
    Mixture screws are 3/4 out on primary side and 5/8 out on secondary side.
    N&S is .110 and float heights are at the bottom of the sight window marks

    Thanks for all the suggestions and advice, much appreciated.

  5. deluxe68

    deluxe68 Well-Known Member

    Was fixing my intake leak and while I already had the carb off I decided to put in a new PV in. I decided to install both gaskets this time and now I have normal mixture screw response. it's been driving me nuts trying to figure out why the engine would not stall when you turned a screw in all the way.
    I remember when I purchased my first power valve, I had called QF about there being two gaskets in the package and
    the tech told me to just run the o ring so that is what I've been doing. Maybe there correct but I'm running both now with better results.

  6. Harry

    Harry The Hammer

    I just put a Q series quick fuel 750 mechanical double pumper on my 78 383 vette & have noticed the stinky exhaust at idle too,the car has a fairly radical cam in it(10hg idle vacuum).I also have had a hell of a time trying to clean up the idle,very very frustrating.
    After closing in the secondary air/fuel screws to about 1/2 turn out it helped a bit but at idle still smells,it runs well throughout the rpm range thank goodness
    My next step is the air bleeds,only 100.00 at the local speed shop.:af:

    Thanks for posting
  7. deluxe68

    deluxe68 Well-Known Member

    Anybody think I can get into the very high 12's?
    Went to E-Town last night, my best ET so far. Noisey valvetrain and all.

    At WOT the a/f meter was 12.5 in second and went down to 12.1-2 in third gear.
    Shifting at 1-2 at 5200 and 2-3 at 5400 rpm which is a few hundred less then before the trans and converter change.


    Attached Files:

    Last edited: Aug 5, 2016
  8. hugger

    hugger Well-Known Member

    12.80s with a 1.68 to 1.72 60' mph is there for high 12's yes
  9. deluxe68

    deluxe68 Well-Known Member

    I'd be super happy with that result with this motor. We shall see if I can get there.
    Running 80 jets with low 12's on the a/f at WOT is acceptable? Not to rich?

  10. hugger

    hugger Well-Known Member

    I would work on the 60' before loosing sleep over the AF, the gain in leaning it out would be very minimal compared to to the needed 60' improvement, what's the converter flashing too?
  11. deluxe68

    deluxe68 Well-Known Member

    Couldn't tell ya. I've heard the terminology, just don't understand it.
    How do you test for that? Is it a sound or feeling?
    I did however leave at 1500 rpm with 30 lbs. of air in the tires.

  12. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    When you foot brake the car at the line, look at the RPM. As soon as you pop your foot off the brake, launch and mat the gas, the engine RPM will flash to a certain RPM. That is flash stall. Are you using Drag Radials? I would start at 22 psi at the track. Go down from there and watch the 60'.
  13. deluxe68

    deluxe68 Well-Known Member

    I'll be testing this on Sunday at E-Town. Running 255/60/15 M//T ET Street Drag Radials.
  14. deluxe68

    deluxe68 Well-Known Member

    Not yet, but getting closer. Best time so far, must have been the Cecil event.
    Maybe the incoming fall air will help a little more because my 60' time are not improving any.

    Attached Files:

  15. deluxe68

    deluxe68 Well-Known Member

    Been messing around again trying to lean out the idle circuit a little more.

    Pri jet 73 / Sec jet 80 / PV 6.5 / IAB 72 / HSB 33 / IFR .030 / Squirt 33 F&R / N&S .110

    A/F readings, fully warmed up

    *Cold start up is in the 14.5-14.8 range maybe for 20 sec or so

    Park Idle 11.8 at 700 rpm / In gear Idle 11.3 at about 600+ rpm

    Cruise RPM's
    1000 11.4 / 1200 12.3 / 1500 15.2 / 1800 14.8 -15 / 2000 15.1 / 2200 14.4 / 2500 13.8 / 3000 13.3

    Was 13.5 at the stripe with Sec jet at 79 at the Atco get together couple weeks ago.

    If I increase the air bleed to 73 trying to lean the idle circuit, the mid range rpm's go into the 16's and it really
    does not change the idle A/F worth noting.

    So the main question I have is, when would it be nessassary to drill .125 holes in the throttle plates?
    or should I turn up the primary idle screw to increase the idle rpm?
    I have both idle screws turned .25 turn from t-slot being square for 6-700 rpm (would like a little more)
  16. sailbrd

    sailbrd Well-Known Member

    first step is smaller idle feed restrictors.
  17. deluxe68

    deluxe68 Well-Known Member

    With the .028 IFR's installed, it won't idle unless I open up both speed screws way past the norm and at that point
    is it not running on the mains instead of the idle circuit?
    This was why I'm thinking it could use more air in the idle circuit.
  18. deluxe68

    deluxe68 Well-Known Member

    I'm going to drill the holes to see if it helps any. Worst case I buy new blades.
    Going to be looking for a carb that has the IFR's at the bottom if the holes do not work out. I know the QF could be drilled and tapped but I'm not going that route myself. I'll send it out and let QF do it. And if that ends up being the case, I'll get a 750 for street use and swap to the 850 at the track.
  19. deluxe68

    deluxe68 Well-Known Member

    Found this comment on another forum having similar experiences with tuning but with a Q750,

    Well guys I had no choice but to call quick fuel today and they said they have had a issue with the metering blocks to were the idle mixture screws have punched through the wells during assembly so I have to take it apart and check and maybe have to get them replaced. They said that is most likely my issue as that would just make it cause all kinds of troubles. We will see and I will get back and let you guys know. Thanks to all who have helped so far. Appreciate always your help here.

    There were no other comments made so I'm not sure of the outcome.
    So how would one check for this "punch through" defect in the block? Does this sound like a possibility if one can turn mixture screws in and it does not stall motor?
  20. deluxe68

    deluxe68 Well-Known Member

    Well if the needle is not supposed to be seen in the IFR channel area, maybe that's the meaning of punch through.
    All 4 needles look like the picture


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