Engine Trouble Four Stroking possible fix! & question

Discussion in '2-Stroke Engines' started by pucksterpete, Aug 5, 2011.

  1. pucksterpete

    pucksterpete Member

    So here is the story: 66cc (strong compression), No air leaks, NT carb, been having a 4 stroking problem at 3/4 to full throttle. Played with different c-clip settings on the needle didn't solve problem. Picked up some jets from SBP, got a 68, 66, 64 & 62mm jets. Tried the 66mm with every position on the c-clip, still the same. Went to the 64mm and have the c-clip set at the richest setting she got better, any other setting she 4 strokes. So, I know these little engines all have different issues, but with the setup now on the carb (64mm jet & richest c-clip setting), is this normal? I know I need to do a read on the plug.

    Has anyone else changed their jets and to what size are you using and setting the c-clip to?



  2. motorpsycho

    motorpsycho Active Member

    one thing to remember is that the c-clip setting has no effect after 3/4 throttle.
    once the slide is 3/4 - wide open throttle, the jet needle is out of play and the main jet is what determines how much fuel the engine gets.

    yes, i've changed my jets(in both of my carbs on my 2 engines) but another thing to consider is that what jet works on one engine, may not work on another engine.
    No 2 engines will run alike and you have to tune YOUR engine by trial and error with different jetting / c-clip settings.
    one of my engines has a .74 jet in it, while the other has a .72 jet in it.
    I can't remember where my c-clips are set, but i know that they are set to different positions for each engine.
    Also, the air density, air temp. and humidity level will also affect your jetting and how the enigne runs.
  3. pucksterpete

    pucksterpete Member

    Thanks for the input. I am going to try the 62mm and see how she acts and read the plug.

  4. Al.Fisherman

    Al.Fisherman Active Member

    I could type a full page explaining what causes, what happens, what it sounds like as to a 2 stroke 4 stroking. The BEST way is for one to listen...this is a great clip explaining the situation.

    Watch this...... http://www.youtube.com/watch?v=0wzph3hL6EE
  5. HeadSmess

    HeadSmess Well-Known Member

    im finding it a nightmare to get my 66 tuned properly.

    came with a 64 i guess. i fitted my 65 from the old engine, was alright but couldnt lean right out. 64 was good. im currently running 60. went all the way to 55 and heres where it gets weird...

    i take off, WOT. if it was too lean it would bog straight away. it doesnt. it accelerates quite nicely but at about 5 grand bogs out. back off a little to 3/4 throttle, it picks up again... so i dont get it :) plug was still dark tan....

    so far, i am not really liking the 66 at all :(

    2 plugs, two head gaskets, already leaking past the third, which is 2mm thick! (loooow compression now) always seeming to be in the same spot making me think theres simply not enough solid metal in the head and it is warping when it gets hot... slant plug. never had an issue with a standard centre plug head. milled the head, the cylinder... all flat. still leaks.

    im getting another 50!
  6. pucksterpete

    pucksterpete Member

    Okay, I have the 62mm jet in, set the c-clip to the 3rd notch running better. Been running a NGK BPR6HS plug, easier to start with. Today, changed back to NGK BPR6HIX Iridium plug and she ran great, no 4 stroking or anything, consistent power through low, mid & full throttle. The only problem is after letting the bike cool down, trying to start it with the Iridium plug, she won't fire. I put the BPR6HS back in she fires right up, but doesn't run as well. Unless, once the engine is warm I can put the Iridium plug back in she will fire up. Both plugs are at the same heat range from my understanding, I don't get it.

    Last edited: Aug 7, 2011
  7. Big Red

    Big Red Active Member

    Four Stroking

    Thanks Al, I found my problem thanks to you. That is EXACTLY what my engine is doing. All this time I thought it wasn't getting enough gas, Now I find out it's getting too much gas or too little air or both. I've been going crazy trying to get MORE gas into it when I should have been, possibly, trying to get less. Or at least trying to get more air into it.
    Now for the $10.000 question. Whats the best (or easiest way) to fix this problem? Please keep it simple as I am just a (pretty good) backyard mechanic.
    Big Red.
  8. bms420

    bms420 New Member

    I'm in the same evil place with my Carb
  9. Big Red

    Big Red Active Member