Question about 2000 Yamaha DT 125 R
This sounds like pre-ignition, ( also called 'detonation' and 'engine knock' ), Carbon buildup on the piston crown gets overheated and then causes the fuel to ignite before the spark plug even fires. This pre-ignition is VERY hard on the piston and crankshaft bearings. You will need to pull the cylinder head and de-carbon the piston and cylinder head..... but I would first go to the dealer and buy a spark plug that is one step colder than the stock plug the manufacturer supplied when the bike was new. Spark plugs control the cylinder temperature, colder plug = lower head temp = less or no pre-ignition. Problem solved? If not, then go to a higher octane gas. Problem solved? If not then install a lower heat range thermostat in your water cooled engine, i.e. go from a 180 degree thermostat down to a 160 degree thermostat.
Posted on Mar 13, 2009
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