Next Step?

Discussion in 'Engine, Fuel and Exhaust' started by Ishmael, Feb 20, 2011.

  1. Ishmael

    Ishmael Active Member

    As I learn more about the mechanics of my bike and attempt to do some of the upkeep and repair myself, I expect to encounter many things which will require a true mechanic or shop for expertise or equipment. I pulled the plugs (original HD 612R) on my 2000 stock Fatboy with 4K on the odometer. The front plug was a nice tan color. The rear plug however had a black sooty appearance which I'm told indicates too rich a mixture. How can this be? Does the back cylinder get the lions share of fuel? The bike runs well, just a bit cold natured. Not knowing what to do I improvised by reversing the plugs. This should tell me if the plug is at fault or something else is going on. First question, how many miles at highway speed should it take to burn the black plug to a tan color if indeed the plug is the problem? After that, what would be a reasonable second step? Compression test? Hoping someone has the time to comment, I thank you in advance.
    PS The only engine change from stock is a set of V & H Longshots, baffles in place.
  2. Ishmael

    Ishmael Active Member

    Thanks Smitty. It was stored indoors always and upkeep by the owner, a certified mechanic. Oil change on the way and the miles will increase as the season unfolds.
  3. Jack Klarich

    Jack Klarich Guest

    May have a look @ valve seals and umbrella seals in the rocker box, if it has low miles and been sitting chances are the seals need to be replaced, they will dry out and become brittle over time, a bit of oil on them keeps them well say lubricated JMO
  4. Breeze3at

    Breeze3at Well-Known Member

    Like Smitty said with todays fuel additives, plug reading is not an accurate indicator. Also, plug reading is done on the insulator, up inside, not on the base of the plug. And YES, the rear cylinder on a carb'd bike does run richer than the front. This is due to the firing impulses of the single crank pin 45 degree engine. The front cyl. fires, then the rear fires 315 degrees later, then the front fires again 405 degrees later. There is more residual fuel in the intake tract at 305 degrees, than at 405 degrees. It's more complicated than that, but that's the best I can 'splain (actually it's the best I understand).

    NEWHD74FAN Experienced Member Retired Moderators

    Black and sooty may not be an issue...and since "functionally" the bike is running okay, you could do a compression check...but I would just change the plugs, and do a close inspection of the connections and wires. I would also do as Smitty recommended and use some Seafoam in the tank and run it on the freeway awhile.

    Hopefully after a few weeks of combined city and highway riding, recheck the plugs...after a freeway run...the rear running a little rich is okay in my gets less cooling so running a bit richer is not a bad thing.:s
  6. brownfoxx1

    brownfoxx1 Active Member

    on older '74 fxe i had the same problem went 1 step hotter on rear plug. test that for a few miles.
  7. ultra...good

    ultra...good Banned

    I run a different plug front and rear on my 74 xlch as well. A j12yc on the front, a j14yc on the rear with the rear being a bit hotter. This helped to even out the color of the plugs, and gave me a bit more power. At the same time, i also indexed the plugs with both electrodes opening towards the piston.
    The front and rear do run a bit different because of cooling capacity. On my 74, the timing is the same for front and rear. On your 2ooo, the timing may be a bit different to compensate for this, i don't know.
    The only reason i did this on my 74 is because i was 18 when i got it, and i had a whole bunch of un-used energy, and i was always looking to go faster. Now, i am too "busy" to change the plugs on my ultra as they have 13500 on them, and are 12 years old. I used to change them every month on the 74. Oh well, figured i would change them on the ultra after i run a tank of gas through it this spring, see how that materializes.

    Good luck with what you do, and please, please, please, let us know what you do and how it works out for ya. Thanks!!!

    BUBBIE Well-Known Member


    I would run your bike like you are doing for now... If it is smooth and Just a bit COLD Blooded... It takes a few miles to warm them up,,, THEN does it run better..?.

    If you notice it NOT running good or Missing, running Rough AFTER WARMED during the ride, I'd suspect a carb related jetting problem OR dirty..

    I would check the compression in the cylds, This is always good information to Know and write it down and Keep it for future reference...
    The pressure on front and back should be with-in a few lbs of each other and the time to crank up should sound and be the same..

    My opinion : the Bike is NOT damaged by its sitting.(.) Good find having that low of mileage on it.
    No oil leaks and running ,,, good thing.

    Swapping plugs is okay to do,, This will tell you a thing or two after about 300 miles I would Pull them and Look... If Not bad or same as before, I would put NEW 6R12's in...
    The 6R12 plugs are the Best stock plug and work GOOD in the HD.. Others swear by Other Brands but Putting in HD plugs and the Stock ones BEST in My Book.. and that is what I ALWAYS use.

    New 6R12 plugs are under 4$ each from HD parts.. Also check the plug Wires,, Your bike IS 11 models old and they could be a problem.. They are also inexpensive from HD and I would Just replace them, keeping old ones for a spare,,, I like the colored ones offered.

    I found that MY carbed 2000 ran great and I would get a few miles on Your bike before worry sets in.... I doubt It to be anything major.. Try a little Sea Foam into the gas tank.

    How many miles have you put on since you bought it?

    Get back later when you find out more....