STILL having engine problems HELP!!

Engine & Related

  1. Collin

    Collin Well-Known Member

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    Still having issues with my 383. Stock HP block, forged crank, diamond pistons on factory rods, comp cam hydraulic roller, ported 906 heads, cast intake, on my 3rd carb. Couldn't get the last dual feed double pumper from pro-systems to run right, so went to a QFT SS-680 dual feed, electric choke. Now running digital point conversion. Running 20 degrees initial timing, and at all in 3,000 RPM at 34 degrees. Running 93 octane fuel.

    Trouble shooting so far:

    Battery had some bleed down issues as it would never hold past 12.4 volts overnight, however after hooking up the gauge to it and driving it gave a 14.5 v reading the entire time.

    Fixed the distributor which seemed to have a little bit too much play as the rotor was making contact with the contacts in the cap.

    Dialed in the AFR almost perfect on idle and in the primary circuit.

    Had an issue with dropping push rods 2-3 times and put a new set of comp hydraulic lifters in. Re-sealed the intake again.

    Heres the issues:

    Around town the motor idles and runs the primary circuit beautifully. Put my foot into the gas for a quick launch and no power and pops through the exhaust OR the carb depends on the day. On the highway, again the primary circuit runs great and I can make decent pulls to maintain highway speed. The SECOND I bury my foot into the gas I lose power and pop through the carb and/or exhaust.


    So thinking it may have been electrical we seemed to have debunked that, now thinking it could either be a valve sticking or intake leak?? Compression test with cold engine and WOT showed 180 PSI in all banks. Compression seems high which may explain a dieseling problem I have off and on.

    Pulling the plugs showed 3&4 were good, the rest are soot covered. The plugs in the back are worse than the ones in the front. Have had the intake off about twice and was careful to reseal the thing up nice. Could I be looking at an intake seal problem? Wondering if it was an intake seal/valve sticking would I have problems just on the secondaries??
     
  2. Russ69Runner

    Russ69Runner Well-Known Member

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    What type carburetor are you running. Is it a single four barrel or do you have a six pack. Might check for a vacuum leak some where. If plug's show black fluffy soot then too rich a fuel mixture. But still need to know the Carburetor set up.
     
  3. Collin

    Collin Well-Known Member

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    Barrels 4
    Booster Down Leg
    Brand Quick Fuel
    CFM 680
    Choke Electric
    Circuit 2
    Fuel System Carbureted
    High Speed Air Bleed 28
    Idle Air Bleed Size 70
    Material Aluminum
    Model SS-Series
    Primary Main Jet 68
    Primary Power Valve 65
    Primary Pump Nozzle Size 31
    Product Type Carburetor
    Secondaries Vacuum
    Secondary Main Jet 78
    Throttle Bore 1-11/16 inch
    Part Number SS-680-VS
     
  4. halftrackman1

    halftrackman1 Active Member

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    Has the heads been milled to much, this will make the intake leak
     
  5. mac

    mac Well-Known Member

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    questions:
    vacuum at idle ?
    choke staying open ?
    engine at temp when problems occur ?
    what plug are you running?
    are you using vacuum advance ?
    what is your dynamic compression ratio?
     
  6. mac

    mac Well-Known Member

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    usually an intake leak will cause a leaner condition. how did you dial in your primary circuit A/F ?
     
  7. Collin

    Collin Well-Known Member

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    Vacuum at idle is 12
    Choke is staying open
    Yes engine at temp when problems occur
    Running Champion RJ12Y plugs
    Yes using vacuum advance coming from manifold
    Will have to calculate dynamic compression

    Primary circuit dialed in using an AFR gauge
     
  8. Collin

    Collin Well-Known Member

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    Looks like the valley pan did not seal well and that oil and air were being sucked in. Only about 500 miles on cam so a pic to show the wear. Going to measure the valves

    15E84050-9A34-4602-A16A-9F1FD7F8B8D7.jpeg

    8F482327-5BA5-4EDE-9B7A-E968E2053FC6.jpeg
     
  9. mac

    mac Well-Known Member

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    i like to put a thin bead of ultra gray on the mating surfaces.
     
  10. Collin

    Collin Well-Known Member

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    We did that. Think it’s an issue when the intake was milled causing a poor mating surface. Going to take the intake to be milled again. Just in time for spring.... :up:
     
  11. droptop

    droptop Well-Known Member

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    Once you get the intake vacuum leak fixed, plan on it running VERY rich on the primaries. If it was running good on primaries with the leak, it had to be dumping raw fuel. That is the reason for the fouled plugs.
     
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  12. Collin

    Collin Well-Known Member

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    9.16:1 dynamic compression ratio
     
  13. Roadcuda

    Roadcuda Well-Known Member

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    I don't think I've heard the term dynamic compression ratio before. What's the difference between that and the numbers you usually hear about?
     
  14. Russ69Runner

    Russ69Runner Well-Known Member

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    You had the intake milled before. If you keep milling it will cause more problem's. The wedge will get smaller and the block wont mate up with it or should I say the head's. Ran into this problem building a 440 motor had to get new head's and intake. We tried double gasket's to close the gap but it would only work for a while then start leaking again. Now day's you might get a size match intake or a little larger and cut it to fit what you have now. Good luck hope it work's out for you.
     
  15. mac

    mac Well-Known Member

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    takes into account the opening and closing of valves to give a more real world number instead of using only the bore, stroke, and chamber size.
     
  16. Collin

    Collin Well-Known Member

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    So just as Russ69Runner stated the engine shop does NOT want to mill the intake. They recommend Indian Head Shellac Sealant by Permatex. They stated that with the metal gasket will be perfect
     
  17. Big John

    Big John Sit back, relax Don't bitch about the cigar smoke

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    Just gonna toss this out there.... On the aluminum manifold for the A12 in 1969, the factory installed a thin gasket on top of the steel intake gasket. I've used them on aluminum manifolds and had good success in sealing them on the first try. They were available from Fel-Pro, but IIRC, I believe the Mopar gasket (if still available) was about half the thickness.

    Some guys use them and swear by them. Some don't feel it's necessary. As I say... Just tossing it out there as food for thought.

    s-l500.jpg
     
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  18. Collin

    Collin Well-Known Member

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    I actually tried to use those the last time but due to the work to the heads and intakes the bolts wouldn’t fit
     
  19. BOB KAMMER

    BOB KAMMER 1969 Road Runner

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    why were you dropping push rods,were they bending? if you milled the heads the pushrods could be to long
     
  20. Collin

    Collin Well-Known Member

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    Bob,

    Dropped push rods because my hydraulic lifters were bleeding down and getting stuck. Defect from Comp that others have reported as well.
     

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