Hi there. Have done piston ring about 10 hours ago, spark plug about 1 hour ago. i also have just done the reid valve as well was ridind the other day and the bike lost small amount of power and now it wont idle below about 1-2000 rmp just dies. any halp would be cool thanks Nathan...
And i have also pulled the carb apart to clean it.
Either your pilot circuit is too lean (colder winter air needs more fuel) or your compression is down. 10 hours on a 125 top end doesn't sound like much but the longevity of the top end depends on many variables including how hard it is ridden, mix ratio, jetting, compression, etc. To me, 10 hours is a lot for a 125.
Where are you located and what is the temperature there? If it ran well in 75F weather and it's now winter, it's likely in need of a larger pilot jet.
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They can do this from time to time. What can happen is the expansion chamber gets pumped with fuel vapor and then can be ignited, causing a large backfire. I hate to attempt to answer your question with a question, but how old is the piston and ring? A ring won't last very long in a 125. For racing, it's changed every race. For joy riding 15-20 hours of run time and it's time for a ring at least. Weak compression can make it impossible to start. If you have perfect compression the cause for the non-start could be something as simple as a burned up or fouled spark plug.
Start by re-ringing the motor (you can do this for about $25 inside of 2 hours time). Clean the carb out, clean the air filter, fill the tank with fresh fuel and replace the spark plug (NGK B9ES - from Autozone for $1.89). If the bottom end of the engine is good, the above steps should get it fired up - providing your ignition system is good, and based on the apparent backfire, I would say you have spark.
Even though the engine is 13 years old but has low hours it could just be that the rings are gummed up and sticking in the groves and not doing their job properly. Before you consider pulling the engine apart for a ring replacement and bore hone, you could try this procedure.
Remove spark plugs and pour some engine flushing product like Wynns or Nulon into each cylinder. Turn engine over by hand to distribute the flush around the pistons and allow to sit for a day or so turning the crank occasionally and adding small amounts as the flush drains past the rings. The flush should soften any build-up of gum around rings and the bore. Before replacing plugs use a torch to see that there is not excessive flush sitting on top of pistons. If so wind over with starter to blow out excess. Replace plugs and put any remaing flush in sump and then fast idle engine until hot and then drain and replace oil and filter (if one fitted).
However if rings are badly worn there may not be much improvement and it is possible the oil use will increase. The cylinder with the badly fouled plug may also have a broken ring/s. Oill changes should be done every year or after 50 hours running, whichever comes first.
Let me know how you get on by posting a comment. Myki R
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