"Cough" when the Secondaries open :(

Discussion in 'Holley' started by sriley531, Sep 21, 2015.

  1. LARRY70GS

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

    A carburetor that has 84 square should have a power valve front and rear. If you eliminate the power valve in the back, you run 8-10 jets sizes bigger in the rear. It should be 84 front, 92-94 back. Shawn, I suggest you pull the bowls and verify your jetting.
     
  2. sriley531

    sriley531 Excommunicado

    I plan on pulling it apart tomorrow and verifying jets and squirters. Stay tuned, and thanks again for all you guys' input.
     
  3. sailbrd

    sailbrd Well-Known Member

    :eek2: that would be like running 94 jets all the way around. That would be a bit rich.
     
  4. LARRY70GS

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

    No, the power valve opens to enrich the fuel mixture at low vacuum. Without a power valve you need much bigger jets. My AED carburetor came with 80 front jets and a front 4.5 power valve. The back had no power valve and 92 jets. If there is no power valve in the rear, you must jet up 8-10 jet sizes.

    http://www.superchevy.com/how-to/74058-carburetor-valve-problems/

    "Power valves are used most frequently on the primary side of a Holley carburetor. They allow the carburetor to operate with much leaner main circuit jetting for part-throttle fuel economy. Then, when the throttle is slammed open, the power valve adds additional fuel, creating the rich air-fuel ratio needed for WOT operation. Most Holley power valve circuits are designed to add the equivalent of 8 to 10 jet sizes of additional fuel. Holley does offer a power valve block-off part that closes the power valve circuit, but this means the jet size must be increased in order to compensate for the lost power valve circuit fuel."
     
    Last edited: Sep 24, 2015
  5. sriley531

    sriley531 Excommunicado

    Ok gents, I pulled off the bowls and checked today.

    The front jets are 86
    The rear jets are 84
    Both squirters are 31

    Analyze away!!!
     
  6. DEADMANSCURVE

    DEADMANSCURVE my first word : truck

    well since its running rich and no rear power valve I almost think I would try knockin the fronts down to 80 , bump the rears up to 88-90 range ( or maybe just swap the front 86 jets ya take out to rear and see how it goes ) . the larger front jet size just seems kinda back-asswards to me .
    and with the secondary "bog" maybe move the rear shooter up to a 35 or 37 . I see those two sizes used quite a lot in some 850's I tear down . the 31 front nozzle seems like maybe ok .
    keep track of your steps . one change at a time , creep up on it - don't go for the home run . then when ya lose a little just back up a step .
     
  7. LARRY70GS

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

    Power valves front and rear? Take a look at the Power Valves and see what they are marked. How much vacuum does your engine produce at idle?
     
  8. sriley531

    sriley531 Excommunicado

    It does have power valves front and rear. I'll have to check the markings and get back to you. Engine pulls about 11" at idle
     
  9. LARRY70GS

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

    Holley tells you to take the idle vacuum and divide by 2 to select a power valve. That's just a general guide though. So you should have a 5.5 or lower valves.

    https://www.youtube.com/watch?v=6vKlAnKdcB4
     
  10. DEADMANSCURVE

    DEADMANSCURVE my first word : truck

    so it does have a rear power valve . well good then . using those 86 jets may help out enough if needed , may not need a big extra shot . jeez I think I got that info from the tech guy ?
    those power valve numbers will probably either be stamped in the metal on the outer edge or on metal ring facing the center of carb , non spring side of PV . sometimes those numbers are hard to make out .
     
  11. sailbrd

    sailbrd Well-Known Member

    I like that plan.
     
  12. 436'd Skylark

    436'd Skylark Sweet Fancy Moses!!!!!

    What size is your engine? Tell us more about your build.
     
  13. sriley531

    sriley531 Excommunicado

    Ok, I've got a #35 squirter and #62-#99 jet kit coming from summit, so I'm gonna start there. Thanks for breaking it down for me Del!

    Larry, I'll check the power valve sizes, tried to cheat and read the numbers without pulling them but no dice.

    As far as more info on the build goes, its a 455 +.030", 9.3:1 cr(actual), speedpro pistons on recon'd stock rods, stock crank, TA 288-92h hydraulic cam, Eddie aluminum heads w/ gessler level 2 porting, port matched Sp1 intake, msd billet dizzy/6al box/8.8 wires, TA supercomp headers, magnaflow exhaust, Muncie m21, 3.42 rear w/Eaton posi and Moser 30 spline race alloy axles.
    Made 532/576 on a superflow engine dyno.
     
  14. Fox's Den

    Fox's Den 355Xrs

    I read along in this and I am with Del and Larry on this swap the front to the rear jetting 84 fr 86 r. 5.5 power valve and the 35-37 squirters on the back. I run a 750 dp myself. But mine has no power valve in the back and I have a jetting that is 70fr. 78r. Larry's discussion.

    When all else fails, go back to the original carbs settings with jets and such and start over.

    I always change the pump diaphragm in the spring just to make sure the pump works good. I have also used the squirters with the tubes on them and they direct the shot directly at the venturies.

    you can also change the pump cams with different colored ones and this will change how much fuel is squirted in carb whether it is on number 1 setting or number 2 setting.

    You can also play with a screw on the carb that opens the secondary throttle blades some and this will help you be able to bring down the idle more with the primaries. Then you can readjust the 4 corner idle system. All 4 screws should be able to slow the engine down when screwed in 1/4 turn from perfect setting. If you open the secondaries too much the idle screws in the back will not function.

    I use a vacuum gauge and a rpm monitor to adjust the 4 corner idle. I do it in gear and you get a better response from the carb. I go for highest reading on gauges, always keeping idle down to 750 or so and done. You may have to go to 800 or so.
     
  15. Mart

    Mart Gold level member

    Try 82's & 92's. 4.5 pv, and 50cc front acc pump, the pump volume works, bog may leave.
     
  16. DEADMANSCURVE

    DEADMANSCURVE my first word : truck

    slept on that a little , i would go a little lighter on front jets initially i think . 80-82 .
    i guess i would worry more about the "rich" , then work on the the stumble .
     
  17. 436'd Skylark

    436'd Skylark Sweet Fancy Moses!!!!!

    Jet the carb down 2 sizes at a time until you get a back fire out the carb on acceleration. Only jet down the main side and only accelerate using the main side. Once it back fires you know you are too lean. That will also clean your plugs. From there jet up one size at a time while reading your plugs. Once you have the main circuit good, put the secondary jets two sizes larger than your main jets as a starting point. Then beat the snot out of it and see what the plugs say. The goal is to run them as lean as possible without damaging the motor. 90% of"carb tuners" don't know that...
     
  18. sriley531

    sriley531 Excommunicado

    Ok gents,

    So based on suggestions here and what I've read/watched on Holley tuning, I dropped the front jets to 82's, bumped the rear jets to 88's, and left the squirters the same. Warmed it up and took it for a drive, the hesitation was still there, maybe the same, maybe slightly worse, not sure. But I also felt it wasn't pulling as hard as before.

    Since I had a nice new one sitting there in the package, I replaced the rear squirter (31) with a 35. Took it for a drive and the hesitation was waaay better. Still there, but far less dramatic than before (again, this is tooling along in 4th gear at 2000-2500 and then flooring it). I ran out of time to play and I dont have any larger squirters, so tomorrow I plan to bump the fronts to 84 and the backs to 90 and see what that does. Again, I'm basing this on the fact that with the 82/88 setup I felt the car was noticeably less strong at WOT. Sound logical to the experts??

    Oh, and also as a bit of a side note, it didn't seem to be puking fumes under WOT like it did before. Not totally sure why as it had larger jets in the secondaries and a larger squirters, but its an observation nonetheless.
     
  19. 436'd Skylark

    436'd Skylark Sweet Fancy Moses!!!!!

    You netted nothing. You dropped the mains as much as you bumped the secondary side. That was a wash do yourself a favor and tune one side at a time!


     
  20. DEADMANSCURVE

    DEADMANSCURVE my first word : truck

    well you did seem to make headway on the stumble thing . so you might be in the right direction there .
    and maybe like joe said - get the primary side set . maybe unhook the left side secondary link and just run on the primary's . you'll run outa steam at a certain point , note the rpm , test run under that . when ya like where ya are then hook it back up and see rpm's where the secondary's start to open , adjust so they start to kick in a little before that rpm point . then on to the WOT secondary adjustments .
    that's all guesswork i'll tell ya . and keep checking those plugs .
    6:00 am , off to a wedding .
     

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