blew it up again, no good!

[miedosoracing]

Oh, you are on a 125. Sorry, I didn't read that if it was typed.  So when was the last crank and piston done?

[MCGRIDDLE_321]

no no.. the bike that blew up is a 07 250sx. i was saying if i was to try and qualify on a 125 for the washougal national it would be hard because im a bigger kid. (195 pounds)

[MCGRIDDLE_321]

i think we did the crank/ top end in like late august, took the winter off. then we replaced the topend in February.

[miedosoracing]

i think we did the crank/ top end in like late august, took the winter off. then we replaced the topend in February.

Yeah, somethings wrong. I'm gonna post a "how to jet soon" when I have time.  I will also try as much as I can to help you. That motor is a good motor. Same bottom end as a 300 even.  Same as my 250xcw and am putting on a 300 cylinder that I just got from ebay. There is something wrong.  Either jetting or lean from something else. Or he didn't put the seals or something in right from when he rebuild the crank, and the air is leaking in somewhere.  That crank should last 5 to 10 years seriously.  The piston should be a once a year if that changed.  I rode a lot and could go a full season when racing pro.

[MCGRIDDLE_321]

just wondering. in the last year i have noticed it being hard to shift out of 2nd when in the high revs. i have to completely shut off the gas and let the revs come down before it lets me shift. it seems to only do it in 2nd gear when revving hard. what do you think could do that or cause that.

[miedosoracing]

just wondering. in the last year i have noticed it being hard to shift out of 2nd when in the high revs. i have to completely shut off the gas and let the revs come down before it lets me shift. it seems to only do it in 2nd gear when revving hard. what do you think could do that or cause that.

Well, could be a shift fork or wear on a gear where it catches.  It would be a perfect time to change that out. Have the guy check all parts inside the gearbox when he splits it.  But it also could be the oil you use.  I have found Mobile One fully synthetic 20/50 to work the best.  That has nothing to do with the motor going though.  I don't buy any of the expensive oils and never will. Our only use is gears and clutch and the Mobile one does wonders. ATF is terrible, I burned clutches up in a day, so don't do that.  It's slick, but too slick.

[MyckMcClung]

LOL Coop, on the Klotz thing. I love the way it smells(the green label Benol) and got almost 80 hours out of a topend on my old YZ, but it's was a PITA to clean up.

On the rebuilds, did you re-torqued the jug, head bolts,and reed block mounting bolts after the break in heat cycles??
This is an often over looked and very important step in break in procedure, as the aluminum jug and head expand when heated up, and contract when they cool. I check/re-torque the bolts after each heat cycle and ride in intervals.

It also sounds like you might have forgotten to turn off the choke

[IllusionGrafix]

ATF is terrible, I burned clutches up in a day, so don't do that.  It's slick, but too slick.

[IllusionGrafix]

I have always ran ATF in my bikes. Never had a single problem as long as I keep it fresh. My 05 is only on its 2nd or maybe 3rd set of frictions ever.

As far as the motor failure goes I duno what else to add. I am gonna have to agree with what everyone else has said for the most part. Maybe a lean problem which led to other problems. Although if I remember right I blew a bike up last time I was at Burnt Ridge too...... maybe that track just has a curse on it!

[snook620]

i think we did the crank/ top end in like late august, took the winter off. then we replaced the topend in February.

Sounds like your either sucking dirt, mixing your gas wrong, running crappy oil, jetted to lean, air leak somewere, not doing maintinence, something....no way that thing should blow up that much.

I used to practice/race the same 125 for 2 seasons and hardly ever blew one up. Thats with me riding atleast 3 days a week and racing atleast 4-6 motos on any given weekend.  I wasnt small or slow either but I worked on bikes every night....maybe them YZs are just tough 

[MyckMcClung]

i've been running Golden spectro10/40 in my tranny since I got bought my 07 kx250 new in 07, It still has the stock clutch in it, I got a new one for the rebuild but the stocker was still waaay in spec. I only change the oil when it's visibly dark or after a ride that involve water crossing.

[miedosoracing]

I have always ran ATF in my bikes. Never had a single problem as long as I keep it fresh. My 05 is only on its 2nd or maybe 3rd set of frictions ever.

As far as the motor failure goes I duno what else to add. I am gonna have to agree with what everyone else has said for the most part. Maybe a lean problem which led to other problems. Although if I remember right I blew a bike up last time I was at Burnt Ridge too...... maybe that track just has a curse on it!

what bike and what type of riding and class. I raced pro 125cc so I was all over the clutch.  It did not like ATF. Whatever works for you, I guess that's cool. But depending on how much you ride and what type, 3 sets in 6 years could be good or bad? Not enough info...   

[factoryX]

I'm sorry, but you don't blow up a motor by sucking in a reed, unless of course your testing out new solid titanium reeds. What destroys cranks, cases, and cylinders is a piston failure, and the majority of piston failures are fuel related. Go look at the motor take pics and post them here, this thread stinks of BS. As for your dad wanting to buy the 4 stroke, fine, its his money. Become the moocher your dad wants you to be... Wish my dad would go buy me a $10,000 clunker ha.

[ACMX]

Factoryx you're right about the reed thing... but I don't think he's bs'ing us. Something is just off.

[IllusionGrafix]

I race pro and I ride a few days a week, a lot in the woods. ATF has just always worked for me and I guess I have just learned to not use the clutch........ momentum momentum momentum! Everyone has their own likes and dislikes. What works for one might be total sh*t for another. :-)