I'm Lost on this one!

Discussion in 'Electrical' started by ccryder, Sep 12, 2014.

  1. ccryder

    ccryder Member

    23
    11
    0
    Hi, I've had a '96 Heritage for about 10 years. It's an 80 inch with an EV-27 cam,modified Keihin carb, .050 off the heads, 2 into 2 aftermarket pipes. Dyna S Dual Fire Ignition. Compression tests out good.
    For a long time now is, that the Rear cylinder sounds like it's missing at idle. The front cyl sound is very pronounced. But, the back cyl. sounds like it hits about every 5th stroke. More noticeable when motor is hot. The rear cyl does'nt warm up as fast as the front either. Now...when I half-choke it when hot, the rear Jug hits Every beat. I've been chasing a possible vacuum leak for years with this issue. Over the years I've changed all intake seals bout 3 times. Intake manifold at least twice. I've changed plugs,wires, you name it. Also running a #60 pilot jet. Plugs burning good.
    The motor is not running on 1 cylinder. It's just weak in the back. Mid range a & hi-speed is great! I just tried this...Closed spark plug gaps down to .025. from .038. Low & behold, The rear fires every time now! I've also had about 3 coils on this ,too. It's now running Great with the Smaller spark gaps. Would my slightly higher compression be blowing out the rear cyl spark? I'm stumped! Any help would be appreciated! Thanks!
     
  2. dbmg

    dbmg Experienced Member

    5,800
    153
    318
    Compression test dry and wet???
     
  3. hobo55

    hobo55 Active Member

    306
    26
    1
    Is the fuel spraying equally into the intake ?
     
  4. Grizzly Old Hippie

    Grizzly Old Hippie New Member

    4
    0
    0
     
  5. Jack Klarich

    Jack Klarich Expert Member

    18,544
    153
    399
    Sounds like a blown head gasket, compression test is in order
     
  6. flst89

    flst89 Member

    52
    18
    4
    Switch the coils around and see if the problem goes to the front cylinder.

    Compression is not blowing out the fire or spark. No way.
     
  7. Jack Klarich

    Jack Klarich Expert Member

    18,544
    153
    399
    Test your coil first,
    You measure a coil between the two small connectors - you should get between 2 - 5 ohms. You can measure between the spark plug hole and one of the smaller connectors and you should get a way higher reading. You should get the same reading from BOTH large spark holes to the small connector.
    A weak spark and or a blown head gasket will make that cylinder run cooler
     
  8. tourbox

    tourbox Senior Member

    1,311
    68
    54
    With a Dual fire Dyna S ign. system you should be running a single coil with 4-5 ohm resistance for street use. What mods. where done to the Keihin(CV) carb? A 60 pilot jet sounds to big. I ran a CV on my TC 95 and only used a #48. Also only had a #45 on a built up Shovel. Do you have the Instructions for the Dyna S?
    tourbox
     
  9. BUBBIE

    BUBBIE Well-Known Member

    4,959
    83
    113
    A WEAK fire from the coil WILL and CAN be snuffed out by Compression. How much CCC is shown on the front and rear... Take it FRESH not what used to be please.

    60 on that jet seems to be MUCH. I have only used up to 48/50 and they were rather Large.
    Your application may be different and need that .060 for other reasons ie leaking intake manifold OR carb to manifold leaks... Very possible.

    The spark and compression DO go together and HIGH compression and Wide set spark-plugs, may not fire. Setting the plugs Narrow where they are now and do fire Both front and rear is a good thing...
    I'd leave them gapped right there where they DO fire...

    How would it run IF you removed the dual fire ignition and just to see How it Runs stock.. (if possible using old parts)

    I ran a Dyna S dual fire in my 97 FXDS and seemed I did have some problems with Spark also BUT that was Long ago...Very LONG ago:bigsmiley15:

    Get back with the ccc and then i'll/we'll go more from there.

    signed....BUBBIE
     
  10. ccryder

    ccryder Member

    23
    11
    0
    Hi Everybody, Thanks for all your inputs. The Top end is fairly fresh, like maybe 1000 mi on it. But, I will do another Compression test again wet & Dry. And, write everything down this time.
    Also what I mean by Dual fire ignition Is OEM. A while back I put enough money together to buy a Ultima Single-fire Ignition. Had nothing but bad luck with it.With the Ultima ....we went on a short trip, and maybe the module got too hot in the cone or something. But, I made it back home, and Returned it as Defective to Jirah Cycles. So, back to standard harley firing config.
    Another thing I want to check is Primary voltage going To the coil.
    I will check more things out, and write again! Thank You!