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Louie, Technician
Category: Motorcycle
Satisfied Customers: 12671
Experience:  25+ yrs. experience
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My son is 15 and rides a 05 KTM 125sx and we are have a

Customer Question

My son is 15 and rides a 05 KTM 125sx and we are have a problem with the bike running great for a very short time then the bike will have no compression. So we are then rebuilding the top end yet again. My son has learned a great deal about how to work on and maintain his bike from a guy who has been riding and working on bikes for years, this guy even went to Suzuki school back in the day. I however do not know 5hat much about dirtbikes at all. I know that all my son wants to do is ride, and having to tear the bike down every couple of weeks to put a new piston n rings in it is not something that we can really afford to do, not to mention how disappointing it is for him. My son saved for a long time to get himself a KTM 125, we even drove to Indiana to get one. When we got home with the bike it had about 150 lbs of compression, 3 days later that was down to about 60 lbs. So when he rebuilt it, we bought a Vertex piston n rings (stock bore). He has put around 15-20 hrs on the bike and now once again, it has no compression. The bike is pretty much all stock. It has a twin air filter, and as far as I know the V-force reeds is the only part that is considered "aftermarket" that's on the bike. We do live in Alabama and the area he rides in is a real dry, powder like dust type of dirt unless it has just finnished raining. We do know that this dust type material is somehow getting past his filter and into his carborator, therefore it's making its way into the cylinder. Also to keep in mind is that he rides with a guy who also is on a KTM 125 but it's an 03 model. This guy doesn't have nor has he ever had these kinds of issues with his bike. He has ridden his bike for almost 5 years now on a regular basis yet he has only had to rebuild his top end once. Like I said, my son is only 15 and all he wants to do is ride, but since his dad passed away I have been a single parent and I just simply don't have the money to rebuild his top end every couple of weeks. Can u please help me to figure out what's going on, what we are doing wrong, what needs to be done so that he can get some seat time on this rebuild. Or if you don't know the answer to my problem could u put me in touch with the right people to figure this out for me. I really appreciate your time and any info u may have to share with me.
Submitted: 1 year ago.
Category: Motorcycle
Expert:  Louie replied 1 year ago.
Hi and welcome to JustAnswer,Thank you for the question and your patience. Should you still need assistance for information purposes only...Initially, the described symptom of "...every couple of piston n rings..." would imply that the engine is not getting enough or too low-grade 2T oil.Proposed preliminary try (if have not been done) is to increase the amount 2T oil in the premix ratio.