Engine Barely Runs

Discussion in '2-Stroke Engines' started by prof fate, Sep 23, 2009.

  1. prof fate

    prof fate New Member

    I have poured though many posts but didn’t find a clear answer, I need a more experienced opinion.

    My engine was running great when I last rode it a month ago and sheared the already upgraded rear mounting bolts. I decided to use that as an excuse to upgrade to the SPB shift kit. And I used buying the shift kit as the excuse to buy a nicer gas tank. I installed the shift kit and the tank and found much to my dismay; I can’t get the booger to run. I am getting spark so that doesn’t look like the problem. Fuel is new and fresh from the pump that day.

    My replacement gallon and a half tank didn’t come with a gas cap so I added some gasket material to the original tank cap to make it fit till the new one arrives from eBay. I considered that my homemade temporary cap might not allow it to vent but that doesn’t seem to be an issue because the cap wobbles and isn’t anything near airtight. I removed the cap while letting the fuel line flow into a catch tank and didn’t see any difference with the cap on or off.

    It’s a 67 cc from Spooky Tooth with the CNS carb upgrade that worked flawlessly when I last rode it. With the shift kit I have to pedal the engine directly to start but I wasn’t able to get it to turn over. I did adjust the clutch to make sure that I was losing any effort due to clutch slip.

    After a good 45 minutes of combined effort over several attempts I swapped the carb out back to the original carb that came with the kit. With the original I was able to get it to turn over a few times and run at low rpm’s. It looked like it was blowing smoke out at the head gasket so I tightened it. I can occasionally get it to run at say 1000-1500 rpm if I give it too much gas it stalls, too little and it also stalls.

    So here is what I’m thinking, if both carbs were working fine when last used, both didn’t go bad at the same time. Fuel /oil mix and spark are not issues. The exhaust is a SBP expansion exhaust and it worked great when I last rode it. Other than the possibility that the intake manifold or exhaust pipe had something fall into them while they were on the work bench that is blocking the airflow, I am totally stumped.

    I plan on taking the intake and exhaust off tonight to see if it could be that simple. But I kind of doubt it. Any suggestions?
    Last edited: Sep 23, 2009

  2. Shadeslay

    Shadeslay Member

    You say you have spark, but how well is the spark. Really sounds like a cdi or magneto issue to me.
  3. prof fate

    prof fate New Member

    Indentifying a weak spark?

    Is there any way to identify a bad or weak spark other that replacing the CDI?:thinking:
  4. MikeJ

    MikeJ Member

    If you want to see spark, remove the plug and hold one of the six sides against the side of the engine. With the CDI connected, you should be able to see spark jump the electrode gap when the engine is spinning. If the engine runs continuously, no matter how badly, the CDI should not be suspect unless the position of the magnet on the crankshaft changed from its default position. I understand the magnet can go on only one way.

    Check for flooding with fuel... Ensure the choke lever is down and not choking air to the fuel supply.

    Check for fuel starvation; a fuel line blockage someplace... Pull the fuel line off the carb. It should run fairly freely. Take apart the carb and ensure fuel is in the bowl. Carefully remove the carb jet/atomizer. Ensure you can see clear through it. (I say that because you put on a new tank (clean it out first?). Do you have a fuel filter? I recommend it. Little pieces of crud keep falling out of the tank over time and may get sucked up by very little orifices of the carb.) Remove the air filter and ensure the carb slide works freely when you twist the throttle.

    On the jackshaft frame: ensure there is a very little side-to-side motion of the shaft, and that it is not binding. Also ensure the teeth of the sprockets line up with the teeth of the corresponding sprocket. The jackshaft must be easy to turn when not chained to the engine.

  5. arceeguy

    arceeguy Active Member

    Replace the spark plug, no matter how "good" it looks, and even if you saw a spark. Too many people have reported the same, chasing their tails, until they replaced the plug andgot the engine running.

    Troubleshooting is a process of elimination, and sometimes we jump to conclusions to find out that the problem was very simple.

    Happy Motoring!
  6. Skyliner70cc

    Skyliner70cc Active Member

    Gasket maker material in fuel line, clogging it or carbs
    Blown head gaket/warped head, loose head
  7. prof fate

    prof fate New Member

    Might be the plug

    The CDI and magneto should be on the door step when I go home for lunch. When I got my graded plug from SBP I think I pitched the stock plug. What type of plug can I use that will actually be in stock at my local auto parts or small engine store? I don't want to add another day or two to my wait.
  8. prof fate

    prof fate New Member

    Hope it's the plug

    Installed the CDI and the new magneto. Noooope. Not them.
    Off in search of a plug that can be bought locally.

    Has anyone ever made a graph comparing your level of frustration (time + effort + cost + bad results) against the cost of buying a new engine?

    I'm not there yet... but I can see where that would be an option.
    Last edited by a moderator: Dec 15, 2015
  9. MikeJ

    MikeJ Member

    Ensure your gap to the plug point is about the thickness of a credit card; it has to be pretty small. Make sure you can see that spark; spin your engine in a dark room. If you can see spark, the CDI and plug are good, regardless of brand, country of origin, or age.

    If spark is present, look at your fuel delivery: fuel line, carb, and any obvious air leaks. More than one rider has done the same path you are following, only to find a problem in the carb.

    Let us know what you find.
  10. prof fate

    prof fate New Member

    Still Searching For Answer

    Mike, I was getting spark before I swapped out to the new magneto and CDI. I had seen several posts that said that it might spark outside the motor but not fire well enough inside to run the engine.

    About the carb/fuel - my thinking (could be wrong) was that both the CNS and original carburetor shouldn't have gone bad while off the bike. Both carbs seem to run about the same. I checked for a wet plug but it is normal. I did swap out my SBP performance plug wire to the new CDI so I guess that could still be the culprit. I will also pull the head to see if there is a gasket problem.

    I found a nearby O'Reilly Auto parts has the NGK B6HS plugs in stock so I am heading over there tonight before they close.

    I am tired of palying mechanic-:( I want to ride!
  11. MikeJ

    MikeJ Member

    You wrote...."...buy a nicer gas tank. I installed the shift kit ...". Before that, all was well.

    Is gas pouring into the carb at the end of the hose at a good rate (an ounce every few seconds)?

    Is your jackshaft turning freely when not chained to the engine? I found on my initial installation that I was pinching the jackshaft components kind of tight; that uses energy produced by the engine. I loosened them and now have about one millimeter of side-to-side play along the shaft.

    Still, check the working of your carb slide by viewing from the air filter end of the carb.

    We hope you find the cause soon.