79cc predator is backfiring out carb and exhaust won't start

Discussion in '4 Stroke Bicycle Engines & Kits' started by Tsears0627, Sep 10, 2016.

Tags:
  1. Tsears0627

    Tsears0627 New Member

    Joined:
    Sep 10, 2016
    Messages:
    5
    Likes Received:
    0
    Okay so I bought this 79cc predator to replace my Chinese 4stroke that the rod snapped in, and I am now having issues with this motor not starting.
    First thing I did even before firing the motor was remove the governor. I followed afg's instructions to the letter. Put it all back together making sure cam was lined up correctly at TDC. Checked the rockers to make sure that the push rods were still in their home.

    The issue now t won't flipping start, I check the plug it's got plenty of spark, and it's getting fuel. I pulled the shroud and pull start off and am using a drill to crank the engine as pull start was killing my arm. The motor is backfiring out of the carb and exhaust is spitting flame :-|| the carb is spitting gas out of it, and I'm at a complete loss please help as this is my only transportation to and from work! zpt:-||laff
     
  2. Tony01

    Tony01 Member

    Joined:
    Nov 28, 2012
    Messages:
    925
    Likes Received:
    17
    Check your valve lash as well! Sounds like the engine may be at full throttle or something with the choke full on.
     
  3. Tsears0627

    Tsears0627 New Member

    Joined:
    Sep 10, 2016
    Messages:
    5
    Likes Received:
    0
    Is there a way to get set valve lash with out feeler gages? I checked them by hand and they move slightly but are under pressure, and as for the throttle going wide open with the choke, that's a yes, but with throttle closed and choke on its still has air pulsing out the carb, is that normal? I'm thinking of just getting a new carb, I've been messing with this for days, and I'm getting very tired of it.
     
  4. Tsears0627

    Tsears0627 New Member

    Joined:
    Sep 10, 2016
    Messages:
    5
    Likes Received:
    0
    Update : with throttle closed and choke on, it's spitting flames our of the exhaust, which is just a straight pipe, from eBay, could it be that there is not any back pressure in the exhaust?
     
  5. FFV8

    FFV8 New Member

    Joined:
    Oct 29, 2013
    Messages:
    552
    Likes Received:
    0
    Is the flywheel key installed correctly? Not sheared?

    You will have to pull the flywheel to check it.
     
  6. Tsears0627

    Tsears0627 New Member

    Joined:
    Sep 10, 2016
    Messages:
    5
    Likes Received:
    0
    Yes the flywheel is installed correctly
     
  7. Venice Motor Bikes

    Venice Motor Bikes Custom Builder / Dealer/Los Angeles

    Joined:
    Mar 20, 2008
    Messages:
    6,167
    Likes Received:
    15
    Double check that the cam gear is lined up with the crank gear properly.

    Also... make sure the valve rockers aren't too tight (you need a feeler gauge)

    Make sure the two dots on the gears are lined up like this...

    image-3232836367.jpg
     
    #7 Venice Motor Bikes, Sep 10, 2016
    Last edited: Sep 10, 2016
  8. Tony01

    Tony01 Member

    Joined:
    Nov 28, 2012
    Messages:
    925
    Likes Received:
    17
    I did not think it was the flywheel as you don't need to pull it to remove the governor. Try starting with the choke off and the theottle closed. Make sure the gas you're using isn't more than a week or two old. Make sure there's oil. So there are flames, and it's firing? Still sounds like a flywheel issue but you say it is good. So I dunno what to tell ya. I have no experience with the stock carb. I also did not run the engine before putting it in the bike. I took everything off it, removed gov, fabbed a new intake and exhaust, took the fins off the flywheel and converted to rope start, and oh yes!! I had the same issues. I had forgotten to tighten the jets in my 19mm carb and it was doing what yours is doing. Now I dropped the bike on the intake side which has caused an air leak... LOL
     
  9. Kletus

    Kletus Member

    Joined:
    Apr 15, 2016
    Messages:
    117
    Likes Received:
    2
    I'll give you 10:1 odds that the cam gear is not indexed correctly. Or the intake valve is stuck open because of a reassembly error.
     
    #9 Kletus, Sep 10, 2016
    Last edited: Sep 10, 2016
  10. Tsears0627

    Tsears0627 New Member

    Joined:
    Sep 10, 2016
    Messages:
    5
    Likes Received:
    0
    I will double check all of this and update you all if and or when I figure out what the problem is, I appreciate all the help and if any one else has any ideas or has had the same thing happened please keep posting the help is much appreciated
     
  11. Slogger

    Slogger Member

    Joined:
    Sep 8, 2014
    Messages:
    545
    Likes Received:
    3
    I had a stuck float needle on a 1600cc Roadstar once. There was dirt holding the needle open.
    It shot fire out of the intake about 2 feet, backfired in the pipes, and made quite a spectacle of us.
    Worth a look.
    Good luck, hope you get it cleared up.
     
  12. Greg58

    Greg58 Well-Known Member

    Joined:
    May 1, 2011
    Messages:
    2,802
    Likes Received:
    42
    Simple question, did the engine run before you did anything? Its always best to start a HF engine before doing anything, getting it replaced may be a hassle if they see you have taken it apart.
     
  13. WECSOG

    WECSOG Member

    Joined:
    Nov 10, 2014
    Messages:
    118
    Likes Received:
    0
    Sure sounds like it's 180* out of time.
     
  14. bluck

    bluck Member

    Joined:
    May 2, 2016
    Messages:
    105
    Likes Received:
    14
    Did you ever fix the issue I'm having the exact same problem with mines
     
  15. bluck

    bluck Member

    Joined:
    May 2, 2016
    Messages:
    105
    Likes Received:
    14
    If anyone wants to know I had the exact same issue and I was able to turn on my engine by adjusting the valves using a feeler gauge at .004.
     

Share This Page