383 stroker timing/performance and temperature

Discussion in 'Troubleshooting & Diagnosis' started by erhan ergin, Apr 25, 2020.

  1. erhan ergin

    erhan ergin Veteran Member

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    One more detail, the increase in vacuum with higher rpm is in no load situation. Essentially car is in park. I read around and this is normal as in no load scenario even with bigger throttle opening, the high flow of air due to high rpm and no load, vacuum looks like it is increasing with rpm. It seems as I put the car in gear there is load on the engine which causes the vacuum to go down. Due to the drop in vacuum engine cannot suck enough gas thru the idle circuit, it gets too lean and eventually dies.
    What is the mechanism in a carb that adjusts this within the same circuit. I presume I am still in idle circuit between 1k rpm and 780rpm right?
     
  2. carhead22000

    carhead22000 oldblue

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    get a laser temp gauge when running check temp on every cylinder.
     
  3. erhan ergin

    erhan ergin Veteran Member

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    I have an IR temp gauge, I did not check individual cylinders but I know it gets worse as the car warms up further.
     
  4. 80sz

    80sz Veteran Member

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    Can add more fuel with idle mix screwsor go back down few on iab .Your still on idle to about 2000rpm then jets start kicking in
     
  5. erhan ergin

    erhan ergin Veteran Member

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    Here is what I did:

    - For the primary side I put back the 65 iab
    - I adjusted the air fuel screws.

    The car is now driveable. In gear it idles around 750-780 and the A/F ratio hoovers around 14-15. As soon as I put it in park it gets very rich. Anything above 780 rpm the car now runs with A/F ratio of about 12.5. If I try to lean it with the air fuel screws the 780 rpm leans out too much and the car will not idle.
    I am guessing if I go to about 72 iab I may get the result I want.
    Is it OK to have different iab in primary and secondary sides? Will this cause issues across the different cylinders (front/aft)?

    Thanks for all the suggestions.
     
  6. 80sz

    80sz Veteran Member

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    I’ve never done that not saying you can’t but mechanical I’d have it square
     
  7. 80sz

    80sz Veteran Member

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    If your in the 1.5 turn area I’d leave iab alone.
     
  8. G72Zed

    G72Zed Veteran Member

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    In reading the posts since my last reply on Feb. 9th, just taking a WAG at this, to me it sounds like you have a large cam combined with not enough SCR, a lack of initial timing, and not high enough stall converter. Dropping in gear loads the engine, looses rpm, then timing goes down, then goes even leaner and drops even more rpm and the cycle repeats itself till the engine stalls.

    This happens even if you do/don't have vacuum advanced connected to manifold vacuum port, worse if it's spark ported, and really bad if you have large runner volume heads with low cranking pressures.

    Since I do not have the time to review all 14 pages, and you have been struggling with this for 10 months now, I'll just give you my thoughts on a typical baseline when starting from scratch on one of these types of carbs.

    Sorry if it's been said already, or it's repetitive, but here it is.

    I would remove the carb, turn it upside down and re-set the primary transfer slots to square by way of the primary curb idle screw, note the width of the transfer by way of feeler gauge comparison. If this has been over machined, or done incorrectly, a transfer slot restrictor may need to be installed.

    Next, set the small secondary idle screw so the throttle plates are just underneath the secondary transfer slots, note the width of the slots. Take this time to tighten all base plate screws, and view the primary blow out protection check ball and spring to make sure it's not cocked in the channel.

    Then, flip it back over and go back and install the original IAB (71) and HSAB 31 if they were changed.

    Remove both metering blocks, gaskets and front power valve. Brake clean and use compressed air to clean all passages of main body and metering blocks. Remove shooters to make sure the steel or brass needles seal and move freely. check shooter passages.

    Next, take a small parts wire, or better yet and small drilling index and check that the upper kill bleeds in the metering block are drilled all the way through (28-31), next, check and note your emulsion package. It should be drilled with 3 holes, (28-28-28?) but the middle should be unfinished and not drilled through.

    Then, note the IFR locations and check it's sizes, note it. Based on your notes and feedback, you may have to perform corrective measures. If it's in the high set position and in the .035-.038 range, there's a major issue. Restrict them to 29-31, or better yet, remove them and install new 6-32 set screws in the 29-31 size the old OEM position. This may be for the more advanced carb guys.

    Its a 4 corner idle setup, start @ 1.5 turns out if your IFR are now in the 29-31 size.

    The idle/HS bleed metering should be kept in balance, so the front IAB and HSAB should be the same. Put in a fresh 6.5 power valve with new gasket and note the Julian date of the PV, if it's "old' get a new one. Mine are all late 2020's now.

    Next, take some black electrical tape and cover your AFR gauge.

    Get your idle timing in the 22-24* range, and 36* all in by 2,600 or so. Get your vacuum advanced limited to 8-10* and install on the "manifold" carb base port so it's active at idle, this should give you 30-34* at idle. Next, install some new plugs, if aluminum heads, try BKR5EGP by NGK, iron, try UR5GP.

    Once the engine if fully up to temp, with a full heat soaked intake, disconnect the vacuum advanced, dial in the 4 corner idle screws to get your highest vacuum or rpm idle reading, keep all 4 idle mix screws the same and in balance, note the turns out.

    Once completed, reconnect the vacuum advance, this will pick up the rpm and clean up and smooth out the the idle most likely.

    If more idle rpm is wanted, go get it by way of the small secondary throttle screw, if less rpm is needed, take it out of the primary curb idle screw. Go around and fine tune the idle mix screws one more time to see if you can pick up a few more RPM's or in hg. Adjust curb idle to lower rpm.

    If your converter is to tight for the cam/CR/head combo and struggles to idle in gear, give the idle mix screws 1/16-1/8 out in all 4 corners, sometimes those combo's just need a rich AFR mixture to keep them running, do not tune to a preconceived AFR number, that's just chasing ones tail.

    If the carb has been corrected, this should give you good startup and full warm/hot idle characteristics, then, remove the black electrical tape and note your AFR gauge for future reference.

    Now it's time to use the AFR gauge to set the PVCR's and mains for max WOT performance and cruise AFR's. Don't even use the AFR gauge to set or adjust your pump cams/shooters, give it what it needs, the AFR's will be what they are.

    If all this has been covered already, sorry for the repetitiveness, I'll delete it to not muddy up this thread.
     
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  9. erhan ergin

    erhan ergin Veteran Member

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    Thanks for the long detailed response. I have gone thru most of this already.
    Some points:
    1- I do not have adjustable IFR, I would have to use string of wires and such to adjust which is not something I want to go into
    2- I have a 2800 stall converter as far as I know. So going from park to gear you would think the loading would not be too much
    3- I have fiddled around with timing quite a bit. I have already adjusted the mechanical to limit to ~ 9 -10 degrees. I also used the lighter springs so it is all in around 2600 rpm. I bought an adjustable vacuum canister but it is not great. It is hard to get precise results out of it. I do connect it to the manifold vacuum but at idle the vacuum is so low it hardly does any advance

    I will go thru some of the steps that I have gone thru already to make sure I did not miss anything.

    Thanks
     
  10. G72Zed

    G72Zed Veteran Member

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    My pleasure.

    I have also changed out the billet metering blocks to the OEM style zinc Holley from a 650/750 (4777/4779) with much better results than the billet ones, perhaps that may be an option for you since your not into drilling/taping and getting into this work, short on trying out a known "good" sorted out carb, or changing the carb out all together.

    Hope you get it figured out.
     

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