Engine not starting, despite good spark

Discussion in '2 Stroke Bicycle Engines & Kits' started by Oliver, Aug 17, 2017.

  1. Oliver

    Oliver New Member

    Joined:
    Aug 17, 2017
    Messages:
    2
    Likes Received:
    0
    My 80cc engine from China (eBay) has not started since it was assembled a week or two ago.

    Fuel is getting to the engine, as the spark plug was wet when checked after cranking - for some reason it refuses to burst to life upon releasing the clutch. The engine will turn over after releasing the clutch level, and sounds somewhat promising, but will go silent as soon as I stop pedaling and pull in the clutch. The engine has never felt hot after trying to get it going.

    I have replaced the spark plug with the NGK B7HS, and am quite sure that the ignition system is working (I pedaled with the plug earthed to the fuel cap, heard a fast clicking and electrocuted myself by accident - seems to me as if its sparking OK outside the engine, just not visibly due to sunshine).

    I reassembled the carburetor, making sure to tighten everything well to avoid air leaks. The throttle mechanism is working.

    I feel like there's not a lot more I can do to fix it without your help - could there be a lack of air getting to the fuel? Any reason for the engine components to be incredibly stiff?

    Many thanks for any help that can be offered!

    Ollie, UK
     
  2. Potato_In_Exhaust

    Joined:
    Feb 2, 2017
    Messages:
    161
    Likes Received:
    1
    Sounds like your fuel mixture is wrong...... most likely running too rich. Also make sure to tighten your head down so you can get good compression.
     
  3. Chaz

    Chaz Active Member

    Joined:
    Jun 3, 2012
    Messages:
    910
    Likes Received:
    36
    Mr. Potato makes good points. You can safely use 32:1 fuel/oil mix. Ignore the factory suggested mix. Read through many posts on this subject to confirm for yourself. Check around the head gasket area for signs of leakage. If you are using the kit supplied acorn head nuts then you can replace them or cut the caps off so the studs have headroom. The acorns can cause the stud to "top out" inside giving you a false torque reading.

    Also you can close the spark plug gap to .022 to see if that helps. And you can try the carb needle with the c clip at the second notch from the top of the needle. Make your changes one at a time so you can narrow down the location or issue of the problem.
     
  4. crassius

    crassius Well-Known Member

    Joined:
    Sep 30, 2012
    Messages:
    3,375
    Likes Received:
    35
    one never stops pedaling and pull in clutch until motor is pulling you along - try full choke and when it pops a few times, take choke completely off and pedal a lot

    first start on a dry motor can be hard
     
  5. Chaz

    Chaz Active Member

    Joined:
    Jun 3, 2012
    Messages:
    910
    Likes Received:
    36
    Excellent advice from crassius above.

    One thing you mentioned about not feeling heat from the engine. You will not feel any heat until your engine has combustion. As in: no fire no heat.

    The stiffness you mentioned is difficult to quantify without a comparison so I wouldn't worry about that until you get her fired up and running.
     
  6. waynesdata

    waynesdata Member

    Joined:
    Jul 10, 2017
    Messages:
    61
    Likes Received:
    2
    I would test for spark again. Start video at 17:05 to skip stuff you do not need.



    2 when you release the clutch the engine compression should very quickly stop the bike if you do not peddle.

    3 check your fuel.
    • Check for vacuum leaks first.
    • Check fuel flow. Remove fuel line from carburettor than open fuel valve over a cup. Do you have good fuel flow?
    • Smell your spark plug can you smell fuel? If not lower your c-clip in the carburettor. That will make your mix richer. My engine will not start in the default position. If that works do a plug chop test. Removing the exhaust baffle will help a mix too rich, but can do damage if you are too lean.
     
    mike carter 2 likes this.
  7. Oliver

    Oliver New Member

    Joined:
    Aug 17, 2017
    Messages:
    2
    Likes Received:
    0
    Thanks for your help everyone - progress but still some problems:

    After putting the choke to the down position (it had previously been up), and running on a fresh fuel mixture as recommended the engine ran for the first time - it was going great, and I had a good few minutes of riding. After idling for a bit, the engine started smoking so I cut the engine. I believe I stalled the engine upon starting off again, and the chain tensioner was forced downwards from its bolted position and the chain jammed up inside the drive sprocket.

    This problem had happened quite a few times previously, but this time I managed to break the nylon wheel when rebolting it into position. Can anybody provide any help with the following:

    -where to buy a replacement wheel
    -options for alternative chain tensioning / links to other forum posts
    -DIY ways to overcome my problems

    I hope that once the engine has been broken in, the stalling should become far less frequent and there shouldn't be as much strain on the tensioning rig. But first I must get the bike back to where I had it before it snapped! Very annoying but not giving up :)

    Many thanks,

    Ollie
     
  8. crassius

    crassius Well-Known Member

    Joined:
    Sep 30, 2012
    Messages:
    3,375
    Likes Received:
    35
    new motors will smoke a lot, both at exhaust and on outside of motor from greasy factory hands - no biggie

    several threads here about everything needed to get tensioner working right
     
  9. Tyler6357

    Tyler6357 Member

    Joined:
    Mar 15, 2012
    Messages:
    803
    Likes Received:
    10
    If you have to run it with the choke on than you need to adjust your carb fuel/air ratio. If you are getting excessive smoke that could indicate that you are running too rich. You should set the clip to the leanest setting and test. If that doesn't work I would try a smaller jet. Also, you should test run it without the air filter, maybe it's clogged up or something.
    http://www.ebay.com/itm/Motorized-B...ash=item3f62af261c:g:44AAAOSw1KxXMX9D&vxp=mtr
     
    #9 Tyler6357, Aug 24, 2017
    Last edited: Aug 24, 2017

Share This Page