Q850 idle tuning help needed

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

  1. deluxe68

    deluxe68 Well-Known Member

    I am super frustrated here, hope someone has another option to try here,

    called quickfuel yesterday and told them I had no real mixture screw adjustment (1/2 turn out x 4 about 13 hg vacuum)
    I'ts been like this for awhile but decided to try to tune this out again.
    I told them the the idle is sooooo rich it almost burns your eyes still even after I changed the IFR from .036 to .031 (last call) and still could not stall the motor with mixture screw seated but if you put your hands over the top it stalls right out.
    He said that the IFR was a big change and was surprised it did not lean it out. He said to do the below items and than change the IAB to .07

    So today this is what I did,

    sprayed carb cleaner in every hole and used small tip on the air nozzle to blow it all out
    all new metering and fuel bowl gaskets
    new 6.5 PV and o-ring front and rear
    new base gasket
    eliminated the pressure regulator (needed to get the filter off the intake anyway) used QF braided fuel rail 6 an fittings
    set T-slots perfectly square ( front & rear speed screws were barely just touching )
    all mixture screws set 1 turn out from seated

    same IFR / primary jetting is 72 / secondary jetting is 80 / IAB is .073 / HSB is .033

    After first start it was able to stay running on it's own and idled around 450 rpm "cold at this point"
    bumped up the secondary speed screw 1/4 turn twice by the time it was fully warm up and the idle was 700 rpm "hot"
    in park and in gear ( no rpm drop at all ) and vacuum advance is plugged.
    fuel bowls are set right in the middle maybe even a hair below.
    I now have 11 hg and still no adjustment in the screws ( I can screw them in all the way but not stall the motor) cover the top and it stalls right out.

    It does have great throttle responce from a stop, slow roll, cruise etc. and a WOT blast in drive shifts at 5000 with no problems and if you manually shift I can hit the limiter at 5500 and it seems like it's pulling harder than before the changes.

    Even though it seems like it's running pretty good there is a very little surge at around an 1800 rpm cruise, not bad but you can feel & hear it.

    So hopefully I have provided a good starting point on the information, so if you have any suggestions please feel free to chime in here.

    Too much carb cfm? maybe wrong style for street use?

  2. hugger

    hugger Well-Known Member

    A full turn out is to much on a 4corner carb for what you have set them at 1/2 then put a half turn on the front speed screw , I have seen a few instances where you can put the rear screws in all th way and just use the fronts. But no the carb is suited to the rest of the setup just fine, take a small piece of wire and run down.the idle air bleeds also a single grain of dirt can destroy idle quality if lodged in there. Id also drop the front bowl level some more just to eliminate that as a issue also
    BuickV8Mike likes this.
  3. deluxe68

    deluxe68 Well-Known Member

    After finding out out there was still no adjustment, I adjusted them back where I had them at 1/2 turn out.

    are you suggesting turn the secondary speed screw back the 1/2 turn to close up the t-slot back to square and
    turn the primary speed screw the 1/2 turn to get the extra rpm at idle?

    I was under the understanding that if the primary t-slot is not square that it then would be running off the mains
    not the idle circuit. True or false?

  4. LARRY70GS

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

    If either pair of throttle blades are too far open, the engine will run on the mains and you will have no adjustment at the idle screws. Try this. Bump the initial ignition timing up to at least 20*, more if you like. Close the throttle blades and try adjusting the idle with the mixture screws. If that works, you need more timing at idle and you will need to adjust your mechanical advance to accomplish that. I now run locked out timing with a start retard. It idles a lot better that way.
  5. hugger

    hugger Well-Known Member

    You can go almost a full turn on the idle speed b4 getting into the main circuit, but as Larry said if you dont have enough initial timing your fighting a losing battle. Leave the Vac advance disconnected for good your combo will appreciate it. If it will take 20 initial and still crank all the better. But yes try to keep the rear blades closed if possible . And yes the more you keep the front blades closed the better but there is a little window of adjustment there to be had
  6. deluxe68

    deluxe68 Well-Known Member

    I have not touched my timing, I have 22* initial and 12* mechanical and advance was disconnected and the vacuum gauge attached to the manifold port.

    I do plan on putting the lock out plate back on tomorrow and check the plugs I just installed last week.
    Mechanical starts coming in around 1000 rpm and stays at 34* from 2600 to 3500 until you blip that throttle a little bit and then you see it advance about 2 additional degrees. I can't tell you if there is any more than that because I really don't like running it that high as it is already.

    I will definitely turn the secondary back and turn the primary in a little maybe but,
    if both T-slots are square and it runs at a rough 450 idle rpm how can I increase the idle rpm with out turning the idle speed screws? And even at this rpm it is still really really rich. How would it be possible to be running on the mains?
    ( there is no fuel dripping from the boosters at idle or when you shut it off) Still have some type of internal leak?

    Do you still think I should add more initial? I don't think I can take any more out of the distributor. 12* mechanical is below the recommended amount from the Mallory instruction sheet.
    I have no hot or cold cranking issues, when it's cold I just have to pedal it a little bit.

    Thanks for all the help so far guys,

  7. LARRY70GS

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

    Something else is wrong then. Are you sure the power valves are OK? Shouldn't run that rich, and you should be able to kill the engine by turning the mixture screws all the way in.
  8. deluxe68

    deluxe68 Well-Known Member

    Brand new 6.5 PV today and o- rings in front and the rear is blocked but put new o-ring in anyway.
    I do have a 7 and some new gaskets I can try tomorrow but I don't think it's the PV.

    I think I'm going to put the t-slots back to square a 1/2 turn on the primary speed screw and than advance the timing until
    I get it to 750-800 rpm at idle.

    If the car takes the additional initial advance with no issues (and I think it will) what would be the problem then? I doubt anybody here is running the initial as high as me. Could it be an overall combo thing?
    Am I over thinking this?

  9. LARRY70GS

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

    Turn it all the way up to 34*. Then see if that clears up the problem. If it does, run it locked out, I do.
  10. deluxe68

    deluxe68 Well-Known Member

    I will, thanks
  11. deluxe68

    deluxe68 Well-Known Member

    Larry sorry but I did not lock the mechanical out today due to having to take the distributor apart. I have already done this three / four times and the pin connectors are not looking good on the male side. As soon as I buy a new three pin breakerless unit I will try your suggestion. I did however lock out the advance.

    car was a little hard to keep running this morning after the changes from yesterday.

    for today this is what I changed,

    another set of block and bowl gaskets, PV and o-rings (7 PV is what I have left)
    shoved some wire down the IAB and HSB restrictions to clear any obstructions.
    turned the the secondaries back to square t-slot and turned the primaries 1/4 turn
    started it up and it ran at 620 rpm and still have no mixture screw adjustments.
    turned in another about 1/4 turn to get to the 750 rpm idle

    put in .076 IAB and could not get the car to run, without turning the mixture screws about 1 1/2 turns out.

    so I decided to put in .070 IAB in and the car fired right up and idled around 680
    was able to adjust the mixture screws in to increase rpm and vacuum to the best of 720 idle in gear (goes up to 750 in park)
    and a bouncing 12 hg at about 3/4 turn out on all four screws.

    Now I can stall the motor with the mixture screws BUT only on the passenger side. Drivers side I can still turn them in all the way with no change.

    Since I put the .070 IAB in, did I not just make the idle circuit richer? Maybe I am experiencing a idle lean condition and not a rich one?

    I know this is super hard to help over the Internet and especially since I don't have a AFR yet, but I thank you all anyway.

  12. sailbrd

    sailbrd Well-Known Member

    Tony, I thought you were getting out of carb weird territory until you said you can only stall it out on one side. You should be able to turn in any one screw and stall it out.

    As you go up in IAB size you will put more air into the idle system and lean it out. I run a QuickFuel carb and we are very close on our settings. My IFR's are .031 and IAB's are 74 in the front and 73 in back (did not have 4 of either) I tune with an AFR gauge and the motor likes about 13.5 at idle. That is about 1 1/8 turns on all the screws. I think you idle mix was so fat that he motor was running on the transfer slots. I think if you keep going up on the air bleeds you will get it dialed in. Don't think you need to lock out the distributor. 22 degrees initial should work fine with 12 degrees mechanical advance. That's close to what I run on a 240/260 Scott Brown solid lifter cam.

    Try a set of 73 IAB's and a turn out on the screws and I think you will have it.
  13. deluxe68

    deluxe68 Well-Known Member

    I have had the stock .073 in the whole time until today. With that if I turned the screws out any more than 1/2 turn the vacuum would start to drop so I never went any further. And the fumes are intense.

    also on the original settings I had both t-slots square and I would turn the front and rear speed screws equal amounts to get a higher idle rpm.but still could turn all screws in without stalling motor. Which made me think I was running on mains and not the idle circuit. That is the reason I started messing with this again.

    I know it sounds weird but I can't explain why left side stalls and right side does not after today changes. Making some progress?
    And another thing weird was when I took off the vacuum gauge hose there was gas coming out of the hose. Meaning of this?

    BTW I did drop the primary float level today to 1/4 up the sight glass.

  14. deluxe68

    deluxe68 Well-Known Member

    Deleted my post from yesterday because they were all false readings that I provided.
    Turns out my timing changed when I put the advance lockout plate in. I had 38* at idle and about 51* total.

    The Mallory vacuum advance arm is longer than the lockout arm, so it pulled all of the vacuum advance from the distributor
    with the plate installed. Adjusted total back to 34* and have about 22* at idle now.

    With the float bowls a little below half, mixture screws 1 1/8'turn out from seated, secondary t-slot square and the
    primary t-slot squared + an additional 1/4 turn I have 680 rpm at idle in park.

    It now has surging at 1800 rpm cruise speed on flat road. Is this the transition area between the idle and main circuit?
    can this be tuned out?

  15. LARRY70GS

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

    Got the vacuum advance limited to 10*? If the vacuum advance adds too much timing it will surge.
  16. deluxe68

    deluxe68 Well-Known Member

    My vacuum canister was full of gas and made me believe it was not even working at that point. so I took it off and put the plate on for now, so I have no vacuum advance right now. But I had to adjust the total timing again due to the arm length difference between the two arms.

    If I can get the idle circuit under control I would think I can always add the vacuum advance back in to gain some fuel economy.

    I am saving your suggestion of locking out the distributor as a last resort, unless it is strongly advisable to do it.
    if I have used your advise in the past when you've said to make one change at a time, so that is where I'm at now.

    I'm just not sure what the next step would be / timing, float height, IAB change, speed screw adjustment etc.

  17. LARRY70GS

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

    Two things can cause surge, too much advance or lean mixtures. If it was me, I'd send this carburetor back to Quick fuel. You shouldn't be having this much grief. All Holley type carburetors can use some fine tuning, but they should run well out of the box, and they almost always do.
  18. deluxe68

    deluxe68 Well-Known Member

    Gave it one last attempt today, and ended up with some positive results.

    I put (4) .070 IAB's in, adjusted mixture screws to about 3/4 turn out for a best vacuum of 12 hg
    then I turned primary and secondary speed screws in 1/2 turn to get 680 rpm in gear and park is about 710

    Took the car for a spin and there is no longer any surge, runs pretty smooth and smells a little better too.
    Even the exhaust note has changed enough for me to hear a difference.

    No problems at all with hot starting but I think with the low rpm I might have some cold starting issues.

  19. deluxe68

    deluxe68 Well-Known Member

    Since I seem to be able not to leave things alone, here's an update.

    #1 was a year old pcv valve hose was causing a vacuum leak.
    It had swelled by the valve so much that it was just sitting there loose (the sp1 pcv set up)
    #2 was a real good one, purchased from Jegs two Quickfuel track packs awhile back and been using them for gasket changes. Ran out ordered more and they came today so I figured I would try some more tuning. Well when I took off the old block gaskets and compared them to the new ones, I found that the IFR holes were way smaller then the new gasket holes.
    the old ones were covering some of the area were the jets are and the new ones are far clear. Same part # on packages also.

    So with the above findings I figured I was extremely lean and not rich at idle.
    Running and smells so much better but have a question,

    I have the primary t-slot almost closed and the secondary t-slot around .020 square and warm idle is around 700 rpm
    If I turn the secondary mixture screws in the motor stalls, good right? Turn the primary screws in and it does not stall.

    but, if you turn the primary speed screw in 1/2-3/4 turn you then can stall the motor and then the idle is to high and the only was to decrease the idle at this point is to turn the mixture screws out but the vacuum drops.

    so my question would be, is it really that important to be able to stall the motor with the mixture screws?

    as of today I'm at / .033 IFR, .073 IAB, .033 HSAB, 72 primary jet, 80 secondary jet, 6.5 PV, screws are turned out about 3/4 turn for 12hg hot and in gear. R44TS plugs gapped at .040

  20. deluxe68

    deluxe68 Well-Known Member

    Q850 is doing better but still having idle mixture screw adjustment issues, if you call it that.
    I'm currently a little less than 1 turn out from seated, if I go in either direction on any one screw the vacuum starts to drop. (I have a steady 12hg at this time)
    if I turn any one screw in all the way it runs sluggish but does not stall the motor out.

    Does it really need to stall? The car seems to me that it is running really good. No hot or cold start issues, exhaust fumes are better than ever, idles at 850 in park & 800 in gear, primary t-slot is square and secondary t-slot is +1/4 turn from square.
    Good throttle responce and has no hesitation or stumble and pulls pretty strong in the +4000 rpm area.

    I am happy with the changes I have made so far but I have a symptom that may or may not require additional tuning help.
    if you unplug the manifold vacuum port on the carb to create a leak the motor picks up idle and the readings go to 14hg

    So since I added additional air into the circuit, would this now be an air bleed tune? or no additional tuning required?


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