Carby 4-stroking but NOT running rich! Help!

Discussion in '2-Stroke Engines' started by jesse52, May 28, 2010.

  1. jesse52

    jesse52 New Member

    Hi everyone,

    I recently got my PK50B engine and I've gone about 65 km on it already (about 1 and 1/4 tanks of gas), it's incredibly fun, but I'm a little concerned. Here's why...

    Ever since I got it it has been 4-stroking. Since I'm a sucker for engine noise, I think it actually sounds pretty good as a 4-stroke, but I want to find out why it is doing it.

    It only works properly when I go uphill or on loose sand when it's getting a hard workout. Wiring seems OK, I had soldered the blue wire to a kill switch, but the black wire is not soldered yet. I don't think that's the problem because it works fine under load.

    I am absolutely sure it is not running too rich. In fact, for a while I actually had it running much too lean because I thought that it was too rich. The spark plug was pure white after a 20-minute run and the silver finish on the engine had even got a bit yellower from the lean heat.

    Any help would be appreciated.


  2. GearNut

    GearNut Active Member

    What throttle position do you have it at when it 4 strokes?
    I ask because most of the time you are probably operating it between idle and 3/4 throttle.
    That is all controlled by the jet needle. from 3/4 to full throttle the fuel is controlled by the main jet. You can easily have the needle clip set to put the jet needle in a sweet spot for most riding conditions, but still be too rich at 3/4 to full throttle if the jet is too big, or plum fell off of the end of the needle jet (the brass tube the jet screws into).
  3. jesse52

    jesse52 New Member

    Yeah... Idle to about 3/4. I don't run it faster than 25kmph/15mph cuz it's still breaking in. I found a place on the needle that is kinda in the middle of lean and rich, going more towards lean. It would be the 2nd position on the needle if the top was the 1st. Middle was too rich, and top was much too lean.

    Anyway, I won't see my bike for the next 2 weeks unfortunately since it's at my family's cabin and we're not going because of very bad weather and my dad not being able to drive the weekend after.

    Thanks for your help,
  4. GearNut

    GearNut Active Member

    They typically will run pretty rough until you go through at least 3 gallons of gas.
    After that, worry about fine tuning and quirky running.
    Patience man, let it break in first.
  5. jesse52

    jesse52 New Member

    That's good to know :D Thanks a lot for the help. When I get to use it again I'll try some more adjusting, and just keep running it until I've gone through that much.