slant six cranks but won't start

Slant 6 Engines

  1. 71dust

    71dust Member

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    I am very new to this so I will lay it all out here.

    I have a 1971 Plymouth Duster. It has been sitting in my grandfathers garage since 1991 and I just got it earlier last summer. I have redone the brake lines and was starting to work all the bad gas out by changing furl filters over and over. I had it running two weeks ago and changed the radiator hoses, fan belt, and antifreeze twice by accident. I then drove it back into the garage and now it won't start. It cranks and tries to fire if I hold the gas pedal, but never takes off. I replaced the carb, plugs, wires, starter, and now am out of ideas. I checked the spark at the plugs and it is sparking. Please if anyone has some help.
     
  2. 67Dart273

    67Dart273 FABO Gold Member FABO Gold Member

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    Basics. Compression, fuel, spark

    Spark, good spark, and at the right time. Check the spark, using a solid core wire, at the coil. Buy a spark tester, or "rig" a probe and grounded clip and test cranking using the key to crank. You should see at least a 3/8 and typically more like 1/2" long spark. Check cranking voltage at the coil + Should be within tenths of volt as same as battery when cranking, and in no case less than 10V

    Check cap and rotor for moisture, grease, cracks, metal erosion other damage

    Even though you checked the plugs, recheck them for fuel fouling or even oil

    ++++++++++++++++++++++++

    Fuel. Sour? How long has it been sitting. Is it GETTING fuel? or is it getting too much, IE flooding from gummed up, stuck needle and seat? Pump the throttle while looking down the throat, you should see the accelerator pump shot

    ++++++++++++++++++++++++++

    Compression.

    Might want to consider what condition the engine is in. Run a compression check, or leakdown test, squirt a small amount (teaspoon) of engine oil into each cylinder to see if this raises low compression if low.

    Other.............Does this have breaker points ignition? Points which sit and corrode is never a good thing.
     
  3. 1970Dart198

    1970Dart198 Well-Known Member

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    Sometimes I use a little Thrust (the can at pretty much any auto parts store) to spray into the carb. Maybe the engine is flooded? If you can smell a strong gas odor under the hood, then its most likely flooded.

    For flooded engines, I take a screwdriver and hold the choke open to let the gas evaporate faster. Let it sit for a little and then try.

    Definitely go over the basics like what 67Dart273 said, you don't want to crank and crank until the battery is dead.

    Also... on the points suggestion, maybe try a Pertronix electronic conversion? It takes away the need for the points ignition system completely.

    Good luck.
     
  4. 73Duster6

    73Duster6 Well-Known Member

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    Check to make sure the plug wires are in the right place. I replaced my Dist. cap one time and put the wires 1 hole forward and it would not start. I realized what I did moved them and it fired right up.
     
  5. 71dust

    71dust Member

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    I am going to check the distributor cap in the morning. I do smell gas under the hood and the plugs had a pretty good gas smell to them when I changed them this afternoon. I just don't understand how it can go from running to won't just that fast. It tries to catch when its cranking it even shakes the car a little, but never enough to full start. Thanks I'll post if I get anything out of it in the morning.
     
  6. 71dust

    71dust Member

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    I have checked the distributor cap and have even taken the burnt edge off the point, but still nothing. I am now stuck with checking the compression in each cylinder I guess. I am in the middle of moving so this is less then convenient but I'll let you know what I find any other advice would be great.
     
  7. nm9stheham

    nm9stheham Well-Known Member

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    You won't get the bad gas out by changing fuel filters; can't be done. You HAVE to drain the tank. After it has set for about an hour, pour a capful (maybe 1-2 tablespoons) of fresh gas straight down the carb throat, and then see if it will start and run a for a few seconds. If it does, then your gas is bad and it all has to come out. It may have gummed up the carb already. Since the gas is very suspect, and it sounds like you havae spark, do this test first.
     
  8. winstoninwisc

    winstoninwisc Taint easy livin free,season ticket ona 1wayride

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    change the points very cheap start
     
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    • moe7404

      moe7404 moe7404

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      my dad had a saying. "check the cheapest and easiest things first" and "check the last thing worked on" thanks dad.
       
    • 67Dart273

      67Dart273 FABO Gold Member FABO Gold Member

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      That actually works. When I was at Miramar I had a part time job at the auto hobby shop, and I found, that usually, when guys asked me for advice, whatever the trouble turned out to be, usually had something to do with the last thing they touched!!!
       
    • demoman3955

      demoman3955 Well-Known Member

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      i have to add my 2 cents on this, because when working on one of mine, i forgot to re-attach the fuel line to the pump, and for some reason it wouldnt start... :violent1:
      I also forgot to put a coil wire back on after messing with the wires. My point is check the simple things before you make it more complicated then it may be.
       
    • racerhog

      racerhog RacerHog likes his Mopars

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      Pull and Clean the fuel tank.... Blow out the fuel lines... Change the fuel hoses.... Change the fuel filter and fuel pump. Open and clean out the carb.... Add new fuel...

      That should fix the problem...
       
    • BillGrissom

      BillGrissom Well-Known Member

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      I'll just copy my answer to the "won't start" post just above yours:

      Next time it acts up, run a jumper from BATT+ to coil+, put an in-line spark tester in cyl #1, if it still won't fire and you see the tester flashing bright (good spark), spray starter fluid down the carb throat and try again. If your starter keeps acting up, replace it with a mini-starter from a Magnum V-8 engine (Ram trucks, Grand Cherokee). They are so light and cheap you can carry one in the trunk. If it runs, don't leave the jumper on long or the coil and ECU will soon overheat. Report back w/ results and we'll tell you more.
       
    • 71dust

      71dust Member

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      I have now moved and looked at it again. I have pulled the fuel line off the carb and into a bottle to see how much fuel is there. there is a lot I filled the 20oz bottle in about 8 cranks. I know there is fuel on the plugs I pulled them replaced them pulled them again and they are soaked. I put the #1 plug which I assume is the one closest to the front and watch as it sparked when it cranked. I was a little nervous as it had gas on it, but no fire. There was a nice spark but nothing big. This now has a new coil, plugs, wires, carb, and starter. I stuck my finger in the hole and felt a little push of air. I will get a compression tester next to check the cylinders. My questions are if one is bad will it not run and what should the compression be reading?
       
    • ph23vo

      ph23vo Well-Known Member

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      bad coil/dist or no power to one of them.. GET SOME HELP!..you are in way over your head ..
       
    • nm9stheham

      nm9stheham Well-Known Member

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      Yes it should run with one bad or weak cylinder.

      Fule pump sounds fine and basic carb function seems oK since you are getting fuel fouling on the plugs. Clenn the plugs with some carb or brake cleaner or alcohol and chekc the gap while you are at it.

      You can do the following tests in the order presented before or after the compression test. I would do these first, as you have a fundamental firing problem that needs to be solved before getting too far with diagnosing one weak cylinder.

      Please do the following: Take the spark wire from the distributor and put a philips screweriver in the end and pay it up on the engine so that the sxcredrive balde is about 1/4" form metal; the purpose is to set up a gap of about a 1/4' and then crank it and see if the spark will jump that gap with a blue spark. If it does, then your ignition and spark during cranking is good.

      Then take some of the gas you pumped out and smell it; does it smell like fresh gas or does it have an acrid, dog-piss kind of smell? If the latter, then the old bad gas is still in there. (BTW, the bad gas, if not gotten out, could have gummed up a valve in a cylinder...).

      Regardless of the smell of the gas, and IF the spark is good, then set the choke butterfly on the carb open and pour a small capful of gas down the carb throat, and then jump in the car, and without touching the gas pedal, try cranking and see if it starts or at least fires a bit. If so, then the carb and/or gas is the problem.

      Please do this in the above order and report what you find.

      And BTW, fore the cmpresoisn test:
      1) remove all the plugs
      2) make sure the tester seals against the cylinder head for each test
      3) crank the engine over 5-6 times (about 3-4 seonds) and stop and take a reading on that cylinder; release the reading on the guage, and test again; do it twice for each cylinder
      4) not having compression tested one of these in a while, I would expect something in the range of 140 psi +/- but the most imporant factor is that cylinders are fairly close to each other
      5) please report the readings on each cylinder here
       
    • BillGrissom

      BillGrissom Well-Known Member

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      If >100 psi compression in all cylinders, it should run. 120 psi is better. I recall the manual says ~140 psi for small blocks. Might be slightly less for slants.

      Why don't they quote compression numbers more solidly? The gage you use can make a difference, both the volume displaced (should match spark plug exactly) and the Shraeder valve in the end (used as a check valve) takes some pressure drop which depends on the spring. Yours should be a special valve w/ white collar (denotes weak spring) made just for compression gages. The other factor is that the camshaft makes a big difference in readings, and people often change those.
       
    • 71dust

      71dust Member

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      \k
       
    • MadMaxCustoms

      MadMaxCustoms Well-Known Member

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      Did you ever figure it out? Having the same problem with my 72 Dart.
      Thanks!

       
    • Blainethemono

      Blainethemono Well-Known Member

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      Drop the Fuel Sending unit on the gas tank and make sure the Filter screen isnt plugged up. That happened with my 72 Dumpster.
       
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