i have a 1999 yz 125 and i went riding today and it ran good.. before it was foulin plugs like crazy so i threw a new top end in there and runs pretty goood.  It ran fine all day then i was coming home through a field (track right downt the road) and it started bogging and fouled the plug. i was holding it wide open. then i put a new plug in it and i kicked it it started and then died right away. same thing happened with the other plugs too. im running 40 to 1 yamalube 2r.. br9eg and br9eix plugs.. the only thing i can think of is maybe the jetting being off.  it kind of felt like it has been running rich all day like random bogging even when i had the throttle wide open.  the float also sticks on it and on the left side the cylinder and cases always get sprayed with oil when im riding i dont know why this is happening besides the float sticking i can take care of that. any help appreciated, thanks

yz125r, on 28 May 2012 - 06:41 PM, said:

Can you please explain what you mean by the highlighted bit, are you saying oil is spraying out from somewhere on the left side of your cylinder onto the left side of your case while the motor is running and you are riding?

Edited by kiwi86, 28 May 2012 - 07:26 PM.

yes! it doesnt look like its from the cylinder though especially because i just did a top end on it with new gasktets and all of this was happeneing before the top end too

From  experience you problem is the Yamalube.  Fouled plugs on it.  Use MotorX at 50:1 and have never fouled a plug again.

Try a different mix and see what you come up with.

For the oil on the crankcase thing, do you have #23 in place?



It's a breather tube that directs spooge from the powervalve down below the frame. Shouldn't spit a lot of stuff out of there, but it only takes a little to make a big mess.

Yamalube doesn't cause plug fouling, unless your jetting way off, plug is the wrong heat range, etc.


Let me see if I read this correctly:
You were running wide open thru a field when it bogged and died? Now it will just fire and die, and the plugs are wet?

If that's the case, I'd be checking compression.

kantoniak, on 30 May 2012 - 10:14 AM, said:

i gotta disagree. plenty of people run yamalube with no problems whatsoever.

if the bike ran ok at some point but now fouls plugs then it's a reed, intake, crank, etc. leak of some sort. if its' always fouled plugs then it may be jetting. you shouldn't have oil outside of your motor. figure out where it's coming from and fix it. once the leaks are fixed if it still fouls plugs then rejet.

i'm betting you've got a leaky powervalve cover. they tend to warp when the bike gets too hot.

i just got a complete top end rebuild new piston cylinder and everything and when it fouled on me i couldnt start it t get home because it would start then it would foul right away again

yz125r, on 30 May 2012 - 12:26 PM, said:

Again, were you running wide open when it died?
You couldn't get it to start because it kept fouling the plug. Were you trying more than one plug? Have you verified weak or no spark?
Have you checked compression on your new top end since it died?


I'm asking because the way I read it is that the bike ran fine all day, then bogged and died while running wide open in a field, and now will not run even with new plugs.   To me it sounds like you may have burnt it up, and your plug "fouling" is just wet plugs and your real problem is lack of compression.



Rich and fouling is normally a stutter or gurgle. Bog is lean, and bog at wide open is lean enough to do serious damage if held WOT.

yeah i was wide open and no i only had a couple plugs that were already fouled and trust me the plug was defintly fouled it was coated in oil over the whole plug.. today i cleaned all the plugs (6) and i went to try them and 1 actually started and then it just quit on me and i pulled it out and it was almost dripping wet with premix and it also did that with all of the other plugs exept it wont start i pull it out and they are very wet and i have not done a compression test on it. the thumb over whole trick is telling me it has good compression.. it also seems with the plugs when i test for spark it will be no spark at first nut then after a few kicks i get spark but then i put it in and nothin pull it out nothin first few kicks but then after a while good spark... these are very wet plugs too...

Get new plugs.


Check your reeds
Do a real compression test
Track down where the oil is coming from on the left side

If all checks out then its time to do some jetting

yes hopefully picking up plugs tommoro and i took a peek at my reeds today and they look good.. not chipped or anyting.. have yet to find that oil leak its just kind of lightly sprayed on the side like just dots of it all over no really heavy spot

yz125r, on 30 May 2012 - 06:11 PM, said:

look for a pinhole in your pipe or a leak on the flange, might be the cause of the oil?

okay will do and anyone know why my plugs are comeing out really wet? then after a few kicks they out they will start sparking then when in the bike it starts then iddles a little bit but if i blip the throttle at all then it dies and wont start again and my plug will be very wet

well i fixed the spark plug problem by lowering the floats and i still cant find where that oil is coming from it on left side cylinder and the cases below that

i would check your powervalve breather hose as mentioned before, Mine spooges oil out onto my skid plate but if yours has a pin hole it could be spraying or wind is catching it and putting it on your cases.

pictures of the oil please

try running a hotter plug
br8es,br8eg or br8eix

also what is your jetting
-main jet
-pilot jet
-fuel screw turns

okay i will get some pictures tommoro when i go riding.. its pouring and storming rught now

thats the perfect time to ride..

lol i dont know it was almost hailing should make good conditions at track tommoro if it runs