Holley jetting / Hesitation off idle
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Thread: Holley jetting / Hesitation off idle

  1. #1
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    Holley jetting / Hesitation off idle

    Ok guys, sorry to bore you with another jetting question, but I have read, watched, searched and listened to helpful friends and I am still no further ahead. I am still unable to eliminate the hesitation in my motor off idle when I hit the throttle (bogging bit*h). The car does pull very strong from mid to top end, but since this is only a street car, the response is very important to me. I have also notice that when I bring the car in from a cruise and the car is around 180 to 190 it seams to idle a little bit higher recently (1000 to 1100RPM). This may be due to the colder weather / better fall air and a possible lean condition?* I did check all of my vacuum ports for leaks and came up empty. Once the car cools down, it will idle back down to 850 RPM.



    Here is the set up:

    Motor (511 CI)

    400 Block
    Comp Cam custom grind solid roller .631 lift in & exh, duration at .020 286 / 292 @.050 250 / 256 110 LSA installed at 105. Valve timing @.050 Int 19 BTDC 51 ABDC EXH 62 C 14 ATDC. (springs installed to match 210 seat pressure with 10 degree locks)
    Forged pistons 10.55 to 1 with 84cc eddy heads & .040" gasket
    RPM intake
    850 DP
    -15cc dish piston. size 4.375
    4.25 stroke with H beam rods
    Zero deck
    Crane roller rocker 1.5 ratio with 1 thread showing
    High volume oil pump and 7 qt Milodon Pan.



    Timing and distributor

    Stock Mopar distributor

    Timing is set to 36 all in by 2200 with 12-14 initial at idle.

    Vacuum advance is disconnected.

    Advance springs are one heavy (looks like it is yellow), and one light.



    Carb

    Brand new Holley 850 DP (4150) mechanical secondary's

    8-9 inches of vacuum in gear. Power valve is and 6.5 (stock with carb)

    Front squirters are 35 rear are 37 (stock was 31)

    Front jets is 81 rear are 84 (stock was 80)

    Curb idle screws checked and remain virtually untouched.

    Vacuum ports have been capped, where needed. PVC hooked up to the rear vacuum port.

    Transfer slots are just covered on both front and rear bores.

    Thanks again!
    Andrew
    *
    [img]

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  3. #2
    Full Member my64dart's Avatar
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    Re: Holley jetting / Hesitation off idle

    Hi,
    Are the accelerator pumps working properly? You need an instint & steady shot of fuel to cover up a bogging engine. I like to use the 50cc accelerator pumps in the primary side. By the way, I tried to reuse those non-stick bowl gaskets & they wouldn't reseal properly. My accerator pump wouldn't squirt right & my engine had a slight miss at idle. I changed both bowl gaskets & things are working much better. Sometimes its the small things that will mess you up.
    Jim
    383 stroked to 432c.i. / 440Source Stroker / Edelbrock RPM heads / 750 Holley / Torker Intake / Lunati VooDoo cam / Dynamic 9.5 converter / Cope Racing Trans / 3:55's with a suregrip /I'm Always Working On Something

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    Re: Holley jetting / Hesitation off idle

    thanks Jim, I think the Holley 850 (4781) comes with a 50cc pump already. I just set the carb to idle and removed it, I am now setting the secondaries up to match the the primaries with the transfer slots slightly exposed. I will know shortly.
    [img]

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    Re: Holley jetting / Hesitation off idle

    Well that didn't help, it made it worse.
    [img]

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    Re: Holley jetting / Hesitation off idle

    The secondaries transfer slots are now closed and primaries are just barely open. I bumped up the primary squirter to a 40 (with the proper screw recommended). That seamed to help slightly, but do not feel that is the problem. I'm starting to think that the 6.5 power valver is too large, but the only one that I have is a 3.5, which I think will be too small.
    [img]

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    Re: Holley jetting / Hesitation off idle

    Your secondary jets are probably too small. I use Comp cams jets on the 800 cfm DP Proform body, of .100 , equal to the Holley #86; with #71 on the primary's, PVCR's is drilled out to .060 each. From the data you supplied, you are lean on the secondary's and too rich on your idle with the giant #81 front jets. The idle is effected by the jetting. That's why my Power Valve Channel Restrictions are drilled out to the max. for when it needs it, not loading up the idle during red lights or staging. Lean is mean, when it gets rich they get lazy, too lean and you top out too soon and misfire before your red line. The motor is an air pump and needs to be tuned like a trombone, you have to have an ear for it, and compensate for the sound. Fuel stand off in the carb. also effects the quality of the run, so you may need a tall air cleaner to accommodate the pulsing. Some use velocity stacks to keep the wind from blowing the fuel off the top, or hood scoops. The old header ads boasted the scavenging effect, will help ram tuning, and were dyno tuned for torque verses horse power using single outlets with collector extensions, not H-piped or X-piped. The X and H pipes are for killing the scavenging, by evening out the pulse for muffler sharing quiet. Two steps forward and one backward, I think! The pump squirter is for tuning the tires and gear to the traction available, the bigger ones dribble out fuel and screw up the idle. unless you can't break the tires loose or bog off the line, don't go up. The power valve of 3.5 is good for cars that have a low idle vacuum of 5 or 7hg, and keeps it lean when running around normally driven (not WOT).

  8. #7
    Full Member 5258's Avatar
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    Re: Holley jetting / Hesitation off idle

    Try a 31 squirter, helped mine.

    Mike
    5258 Performance* Shelbyville, Tennessee "Where the MOPAR factory built and race ready hotrods live again"

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    Re: Holley jetting / Hesitation off idle

    Quote Originally Posted by 5258
    Try a 31 squirter, helped mine.

    Mike
    The carb cam stock with the 31, which is where I started 1st.

    Thanks anyways
    [img]

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    Re: Holley jetting / Hesitation off idle

    Quote Originally Posted by Winter
    Your secondary jets are probably too small. I use Comp cams jets on the 800 cfm DP Proform body, of .100 , equal to the Holley #86; with #71 on the primary's, PVCR's is drilled out to .060 each. From the data you supplied, you are lean on the secondary's and too rich on your idle with the giant #81 front jets. The idle is effected by the jetting. That's why my Power Valve Channel Restrictions are drilled out to the max. for when it needs it, not loading up the idle during red lights or staging. Lean is mean, when it gets rich they get lazy, too lean and you top out too soon and misfire before your red line. The motor is an air pump and needs to be tuned like a trombone, you have to have an ear for it, and compensate for the sound. Fuel stand off in the carb. also effects the quality of the run, so you may need a tall air cleaner to accommodate the pulsing. Some use velocity stacks to keep the wind from blowing the fuel off the top, or hood scoops. The old header ads boasted the scavenging effect, will help ram tuning, and were dyno tuned for torque verses horse power using single outlets with collector extensions, not H-piped or X-piped. The X and H pipes are for killing the scavenging, by evening out the pulse for muffler sharing quiet. Two steps forward and one backward, I think! The pump squirter is for tuning the tires and gear to the traction available, the bigger ones dribble out fuel and screw up the idle. unless you can't break the tires loose or bog off the line, don't go up. The power valve of 3.5 is good for cars that have a low idle vacuum of 5 or 7hg, and keeps it lean when running around normally driven (not WOT).
    So your suggesting to go down on the front jets to a 71? and up to an 85 in the secondaries?
    [img]

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    Re: Holley jetting / Hesitation off idle

    If you drill out the PVCR to .060 then you may try the primary jet in the #72- #80 range. The pump shooters @ .031 for a base line, the secondary jets #86 and higher. Power Valve @ 6.5 cause your idle is 8-9 hg.* The bigger CFM carbs (850-1050) need bigger jets than the 800 and smaller. A big difference is in the larger throttle plates.

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    Re: Holley jetting / Hesitation off idle

    * your intake pan gasket mite be leaking,I have almost the same motor with a smaller roller cam a have a 4781-5 carb. 37tube squirters,it has 2-50cc pumps now.It came with 30cc and 50cc in back. * You must have a high stall and it mite need a different pump cam,it mite be squirting before its needed. that 4781 has different sub-fixes -2 -3 -4 and -5 that I have some call for different jetting, go to mortec.com and find your carb.,mine calls for 80f/78s in back now a have 80/79s I don't think jetting is the problem,but if you have both powervalves you don't need over 3 jets bigger,if you do you need a bigger carb. Last week I put a 2"spacer so I put 83s/81s it ran 6.36,then 6.39,then put 80s/left the 81s in back the next pass was a 6.325 breakout on a 6.35dial-in. So for next race I put the 79 back in the back. I thought the spacer needed more jet, not true not my motor.

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    Re: Holley jetting / Hesitation off idle

    Thanks speeder440. What is the best way to check for vacume leaks? I am running a 9 1/2" 3200 dynamic converter. I think the carb is a 4781-1 (bought it from Summit 4781C).
    [img]

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    Re: Holley jetting / Hesitation off idle

    I would change the ignition curve. You have to much mechanical advance. It will idle better, and help with that hesitaion. Actualy, the idle is NOT affected by the main jet. The main jet will definately have an affect on off idle response though, until the PV opens. Drilling the power valve channel restrictions bigger, to install a smaller main jet, will make the hesitation worse. It could be the power is opening a bit late, which will also cause a hesitation. with 9 inches of vacc at idle, it could be just a bit late. If anything, you would want to try a higher number, like a 7.5 if it has 9 inches of vacc. This is what i would do, before you go drilling any holes open. Put the 7.5 pv in it, see if that cures it. If that doesn;t do it, add 2 or 3 numers of jet on the primary side. then manualy turn the timing to about 22initial. Don;t go winding the thing to the moon, but just see if the hesitation goes away. Keep in mind, you will have 46 total, if you wind it up, so, this is just a quick little test. Jump on it off idle, and thats it. If it helps, which I am sure it will, then, you need to change the timing curve. Those are the changes I would suggest. The pvcr mods can be done after you get the other stuff working, to help lean the cruise afr a bit, but don;t get to crazy. Very small changes at a time. If you go to far, you will have elevated egt's cruising, which will cause overheating issues, and ex valve problems. There is a fine line to get the correct wide open afr's, and, have a rich enough cruise afr, without being to lean, and have a problem. If the power valve deal helps, but it loads up at cruise, because its right on the edge, you can go back to the 6.5, and add a the jet on the promary side. Thats what I would do



    Frank

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    Re: Holley jetting / Hesitation off idle

    Thanks Frank, I have not tried reconnecting the vacume advance, should I give that a try first?
    [img]

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    Re: Holley jetting / Hesitation off idle

    Hi,
    My guess is also an intake manifold leak. With your setup, you should be lighting them tires on fire.
    383 stroked to 432c.i. / 440Source Stroker / Edelbrock RPM heads / 750 Holley / Torker Intake / Lunati VooDoo cam / Dynamic 9.5 converter / Cope Racing Trans / 3:55's with a suregrip /I'm Always Working On Something

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    Re: Holley jetting / Hesitation off idle

    Quote Originally Posted by my64dart
    Hi,
    * *Are the accelerator pumps working properly? You need an instint & steady shot of fuel to cover up a bogging engine. I like to use the 50cc accelerator pumps in the primary side. By the way, I tried to reuse those non-stick bowl gaskets & they wouldn't reseal properly. My accerator pump wouldn't squirt right & my engine had a slight miss at idle. I changed both bowl gaskets & things are working much better. Sometimes its the small things that will mess you up.
    * * *Jim
    Jim,one of my friends with a 446" had this same problem,we found that the pump arm was hitting the hex fitting on the fuel line. all we had to do was turn the fitting a little,it was clicking on the pump,after that it worked like new. I use 34* locked down I have my Eddys milled .040",flattops .010" in the hole,.038" gaskets. 308*street roller,3600stall,456gear, and Johnny Lighting Holley850---good thing I race 1/8 mile shift@5700 and out the backdoor
    l

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    Re: Holley jetting / Hesitation off idle

    Sounds like intake leak to me also. I had the exact same problem..tried everything from carb changes to timing and distributor changes. Then realized I had not checked the intake. I used the the pan gasket and the fiber gaskets too. I used gasket cinch to hold the gaskets together in a sandwhich then bolted down the intake. No more stumble. Just because the intake bolts are snug doesn't eliminate the possibility of a leak. Check it out.
    LOOK STOCK BUT SWING A BIG ARM

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    Re: Holley jetting / Hesitation off idle

    Thanks guys, I have no problem frying the tires, but feel it could be more responsive. I tried hooking up the vacume advance, it caused the motor to idle funny and seamed to be all over the place, I even lubed the felt under the rotor. Disconnected it again. I will try to "snoop" for leaks again tomorrow. Lots of great ideas and suggestions here. I'm learning a few things along the way. Thanks again.
    [img]

  20. #19
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    Re: Holley jetting / Hesitation off idle

    Hi mrpat,
    First, the vac advance will effect idle, but not your hesitation as it will drop out when you stab the throttle.

    Like Frank said, if you run more initial timing it will help.many dizzy's have a setting on mechanical advance, so
    you can run 20 to 24 initial and still limit total timing to 35-38 or so.

    I believe your transition fuel is lean, which takes you from idle to the power circuit.
    This is part of the idle circuit, effected by idle air and fuel restrictors.
    This being on the lean side and the speed through the boosters could cause your hesitation.

    The fuel movement through the main boosters is tuned from the emulsion,
    and air bleeds. A small amount of change here can speed the fuel movement through
    the booster. HP holley's have changeable bleeds.

    Here is a good read on how this works. Try some small changes in the bleeds.

    Rick
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  21. #20
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    Re: Holley jetting / Hesitation off idle

    Thanks Rick! I will do some more reading and let you know what I find out. I hope to have it figured out before the Snow hits up here.
    Andrew
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