KX125 bogging down then races off

[txsteele]

I know the title was kinda funky but that's the best way to describe it.

When I open the throttle, the bike takes off like a fire is lit under it. Half way through the rev cycle it Boggs down for a "2 or 3" count, but if the throttle stays wide open, the bike catches and takes off again like nothing is wrong with it. It's an older bike (2003) so I'm giving it some TLC as I do a budget rebuild. I'm hoping this sounds like a carb issue to you guys.

Additionally, after every time I ride it, no matter how long of a ride (2 minutes or 20 minutes), there is always black oil/gas residue running down the bottom of the silencer.

Any opinions would be appreciated.

I did a search on "bogging" before I posted this but all the threads were super long so I couldn't find the answer I was looking for. Thanks.

[Foxx4Beaver]

You could try thoroughly cleaning the carb, and writing down the current jetting.

Probably should do a leak down test if cleaning the carb has no affect...it could have a bad crank seal.
You said the silencer is leaking sponge...which could be a result of a bad crank seal....sucking tranny/gear oil. Does it appear to be using tranny oil, or does it stay at a consistant level?  

[txsteele]

You could try thoroughly cleaning the carb, and writing down the current jetting.

Probably should do a leak down test if cleaning the carb has no affect...it could have a bad crank seal.
You said the silencer is leaking sponge...which could be a result of a bad crank seal....sucking tranny/gear oil. Does it appear to be using tranny oil, or does it stay at a consistant level?  

I haven't checked that yet but I will ASAP.  It's a new bike to me so I did change the oil when I got it but haven't ridden too much since. I suppose that would be a place to start investigating. Thanks.

[Foxx4Beaver]

Be sure to verify the float height is correct too when cleaning the carb.