Mystery Bog

[jdc9q8]

Ok, I've read just about every jetting/bog post on this site and have put hours into this bike.

It's a 97' YZ 125..

When I bought it, he said I want a bigger bike, this one is underpowered..it won't climb hills...

I assumed it was jetting. I ride around 500-600 ft above sea level.

Before I bought it had been rejetted..330 main, 50 pilot, clip position was second from top..and v-force reeds with a procircuit pipe

I am running really rich..when on a slight incline at all it will bog out and die instantly..absolutely no power at all...a 50 cc bike will kill me up a hill...it also bogs from stop to WOT on asphault, spooge/black buildup is coming out of the exhaust..

I attempted to rejet but can't get a lean plug..i went from 330 to 310 to 290 and then out of control to a 250 to try to get anywhere near a lean plug..still fouling and bogging out...

I've checked the reeds, powervalve, carb is extremely clean no dirt, compression is around 130, running b8 plugs, 30:1 ratio with 93 octane...

Does anyone have any suggestions at all? (crank seal, silencer, ??)

 

[sixds]

move it a clip or two up on the needle in the carb. also, make sure your carb is clean.

 

[bdtoady22]

check your float level. it sounds like that is the problem. if that helps and the black spooge dosent stop then check the crank seal. also you would be smokin like a frieght train and tranny oil would magicly dissappear if it was the crank seal on the right. on the left it would be uncontrollably lean, not rich

 

[bdtoady22]

i have a stock 94 125 and i run on the leanest needle setting and a 320 main and it is darn close

 

[_JOE_]

Tranny shaft seal? If it's burnin gear lube it'll run like sh*t. Also causes people to suspect rich jetting.

 

[jdc9q8]

what about a low voltage stator or timing is off?

 

[Jeromeo]

that sucks dude. My yz125 will scream up a hill and climb them really well. Does it seem to smoke alot more than normal??If so like others have told you it could be the crank seal. Check float level as well like others have said. I run 32:1 with BR8ES plugs.

 

[jdc9q8]

i've checked float level...it's fine...i'm runnin the same plugs same ratio...yah it smokes and fouls plugs within minutes...thanks for the post though i was wondering how other 125's do on hills..what about if your stopped on a hill and try to start up it?

 

[bdtoady22]

probabaly not must people don' mess with the timing. i say its the float level. you said that when you start up a hill it bogs so hard that it dies. classic signs that the carb float is to high allowing to much gas in the mix, actually its flooding the cylinder, therfore creating a way rich plug which jetting will not cure...

 

[bdtoady22]

mine is a rocket. 125's dont have alot of bottom end so i get a hell of a run and keep it pinned

 

[jdc9q8]

I've decided it's the crank seal...by eliminating every other option i have come up with..i filled the crank case with a quart of oil..ran it for a while..drained the oil and have 740 mL's (started with 946 mL)...it's pretty obvious to me that the crank seal is shot and developing a rich condition...i've been researching on how to replace the seal without splitting the cases..i'm hoping the bearings aren't bad so i don't have to go to extremes...anyone know if i can replace the right crank seal without splitting the case on my model bike?

 

[bdtoady22]

yeah you should beable to replace it without splitting the cases. i did. you have to take off the side cover take out the clutch and basket and the primary drive gear. there is a collar on the crank shaft that the seal rides on check it out good also. if itbis wore you can flip it around and reuse it. if its been flipped already better replace it. its like 11-12 bucks. also make sure that you put the seal in right. to remove the old on i use a hooked pick and very carfully pulled it out with out damaging the crank. ive heard a lot of people drill holes in it and run sheet metal scews in but ive never used this method. it sounds alot harder than it is. good luck. also i would put a 320 or 330 main jet back in before you run it cause a 290 is way to lean. just a suggestion. i have a clymers manual and it cover 94 -00 yz 125s so yours should be the same