View Full Version : rs 125 extrema 03 keeps running off any ideas

06-21-2009, 05:15 PM
hello all im new here so bear with me ive just bought a mint rs 125 extrema on an 03 plate got it home started it all was fine untill i took it out on the road got to about 75mph an the back wheel locked up which was a little scary i worked out that there was a problem with the oil feed to the pump had not been bled properly i sorted that got it running it sounds sweet when its running not like i would imagine a seized engine to sound but now it wount start unless i bump start it and when i do eventualy get it going it just runs off im new to 2 strokes so dnt no loads about them. the way it runns off sounds like fuel starvation not an engine seized but thats what all the bike shops are telling me im a diesel mechanic by trade so i know how most of it works but would i would appreciate sum of your insight on this as im a little stumped now ive checked the fuel feed to the carb thats fine its also got fresh fuel the spark plug has a good strong spark ind is a stone grey colour which i belive is ok im getting a compression tester to test the compression if any one knows of anything else i can check before i have to drop the engine out please let me no many thanks john

06-22-2009, 01:05 PM
My guess is you need a new piston and ring. You're loosing compression because the ring is jammed partially by the "seized stripes" on the piston. Your compression is just low enough to not kick over with the starter, but still enough to light off at higher piston speeds. I'll guess it's read around 90-100psi on the Compression tester.

I'd expect it to need a light hone on the cylinder wall too.