Two Stroke Motocross

Two Stroke Motocross Forum => Technical => Topic started by: smaltz138 on December 21, 2011, 10:27:52 PM

Title: Yz250 2011 problems
Post by: smaltz138 on December 21, 2011, 10:27:52 PM: So here goes. Got tired of 4 stroke problems, got two 11yz250 . Use bellray h1r 32:1 with 93 octane non ethanol gas. One bike destroyed 2 pistons each within 10 hours. The other bike just broke a piston on the top, above the ring exhaust side.?
Checked fuel cans and tanks yes oil mixed. Air boots super clean, filters changed after each ride.
any info would help. We have been heavily involved in mx for 11 years and this is a first.
?
Thanks
Title: Yz250 2011 problems
Post by: cnrcpla on December 21, 2011, 11:23:32 PM: Try looking for any debris in your bottom end. OR check the screws where your red valves attach to the reed cage. I have heard of those breaking off and wreaking havoc on the inside of an engine.
Title: Yz250 2011 problems
Post by: smaltz138 on December 21, 2011, 11:29:54 PM: Thanks, all good, less than 8 hours on the one bike
??
Title: Yz250 2011 problems
Post by: coblefutch on December 22, 2011, 12:54:04 AM: did you try clicking that lever on the left side of the engine up once in a while?
Title: Yz250 2011 problems
Post by: factoryX on December 22, 2011, 01:12:59 AM: Jetting sounds like a great place to start.
Title: Yz250 2011 problems
Post by: xandyx on December 22, 2011, 01:24:13 AM: did it scored the cylinder? maybe the jetting is too lean..

did that happend with cast of forged pistons?
Title: Yz250 2011 problems
Post by: cnrcpla on December 22, 2011, 01:34:06 AM: If not the jetting then maybe you have an air leak between the carb slide and the intake port. Does it want to rev up on its own when you start it?
Title: Yz250 2011 problems
Post by: smaltz138 on December 22, 2011, 01:35:26 AM: OEM pistons, stock jetting. Bike properly ridden by aggressive amateur national rider with 11you years racing experience.
Title: Yz250 2011 problems
Post by: smaltz138 on December 22, 2011, 01:48:33 AM: Thanks checked for air leaks, also this is 3 pistons on 2 different bikes. After rebuilds we going to switch to cam2 and maxima 927.
Title: Yz250 2011 problems
Post by: Toadmeister00 on December 22, 2011, 02:35:57 AM: I'd do some digging on Thumpertalk, I seem to rememeber reading about timing issues on the YZs. The piston problems could be a result of too far advanced timing.
Title: Yz250 2011 problems
Post by: SachsGS on December 22, 2011, 04:39:37 AM: Pictures of sparkplugs and damaged pistons?
Title: Yz250 2011 problems
Post by: TMKIWI on December 22, 2011, 04:53:10 AM: I wouldn't bother switching oil brands , nothing wrong with Bel Ray.
I would be checking for, filter not sealing properly, Ignition timming, Check the carb anyway just incase something was wrong from the factory.
Your bike wouldn't be going thru pistons for no reason.

Quote from: SachsGS on December 22, 2011, 12:39:37 PM
Pictures of sparkplugs and damaged pistons?

X2
Title: Yz250 2011 problems
Post by: MXLord327 on December 22, 2011, 01:56:40 PM: I have read in a few magazines that the newer YZ250's are jetted pretty lean stock, right on the edge of detonation. Possibly try a 50/50 mix of leaded race gas and pump gas???
Title: Yz250 2011 problems
Post by: GlennC on December 22, 2011, 03:54:33 PM: Quote from: smaltz138 on December 22, 2011, 09:48:33 AM
Thanks checked for air leaks, also this is 3 pistons on 2 different bikes. After rebuilds we going to switch to cam2 and maxima 927.

I used to love bel ray products... Went through 3 pistons in one year on my CR250 using H1R. Same story mixed properly, good air seal, name brand pistons. All machine work done by LA Sleeve (They are good).

I switched to Castor 927 3 years ago, and haven't siezed a piston since.
My current bikes are a 2010 YZ250, and a 2004 Service Honda CR500AF. Both of them have many hours with no problems.

I would still check the jetting though.
Title: Yz250 2011 problems
Post by: smaltz138 on December 22, 2011, 05:30:05 PM: Hey, thanks. From what I read and hear from others, must have been fuel. Going to switch to cam2, and will update next week.
Thanks
Title: Yz250 2011 problems
Post by: cnrcpla on December 22, 2011, 07:58:56 PM: Good luck
Title: Yz250 2011 problems
Post by: smaltz138 on January 02, 2012, 02:43:38 AM: went south with rider for the past week. Mixed 3 gallons race gas with 2 gallons 93 pump gas 32:1 bell ray h1r. He rode alot, lol, burned 20 gallons through practice bike. Problem solved. Stock yz250 will not last on pump gas if ridden aggressive. Met another guy who had same problem and fixed same way.
bike is awesome, just run min 100 octane fuel.
thanks for replies
I hope this helps some others.
Title: Yz250 2011 problems
Post by: factoryX on January 02, 2012, 06:42:46 AM: What engine work has been done? In 2011 they lowered compression, and my 03 (Same engine up till 2010) runs just fine on 93 octane ethanol free pump..
Title: Yz250 2011 problems
Post by: cnrcpla on January 02, 2012, 03:57:36 PM: Same here... my yz takes the 93 pump gas and it is fine. I even ran it on 83 once by accident and it still ran fine. But 93 is best for me in my opinion.
Title: Yz250 2011 problems
Post by: smaltz138 on January 03, 2012, 06:53:50 PM: All stock except pro circuit pipe on race bike, fmf pipe on practice bike.
Also met a guy at south of border training facility who just had same problem with same bike and he switched to race fuel mixture and all is good.
Thanks, Good Luck
Title: Yz250 2011 problems
Post by: hack-man162 on January 11, 2012, 04:19:05 AM: Mine detonates on pump gas. With RAD Valve (spacer removed) and DEP pipe/silencer. Race gas makes it very happy!