Hello, first time posting. My son's kfx90 has been running fine (bought used about 4 months ago. not sure year, 2010?) but yesterday started bogging down when throttle applied . idles fine and will start to move then bog down. are there some trouble shooting suggestions. Im trying to research this forum but thought I would ask. Thank you

 

Probably a partly blocked main jet in the carb, but fit a new plug for a start, can't hurt. If that doesn't work clean the carb out. I remove and blow the jets, and the holes they came from, out with compressed air. Clean the float bowl, assemble, and see how it runs.

 

thank you for the response. Is there a good DIY tutorial on doing this?

 

Probably, and there will be lots of bad ones too. Fairly straightforwards, Turn fuel tap off and separate the fuel line from carb. Get carb separated from manifold and air box (if it has one). I don't take cables off unless they are too short to allow me to turn carb sideways to unscrew the float bowl screws. A good fitting screwdriver is vital.Once bowl is removed there are two brass jets dangling into it in the centre of the float. Remove the one with a hexagon with a spanner, this has both jet and emulsion tube, blow it clean with compressed air and check you can see through the main hole in the end. Blow up the hole it came out of. The other jet is usually just slotted, and quite often the head is up a chamber, so a straight sided screwdriver of the correct size is needed. Once that is out, blow it and the hole it came out of, out with compressed air, check you can see through the jet, replace. Clean the float bowl out and refit that, blowing any holes in it out first. I don't remove the float unless the carb has been dribbling, and be careful not to catch it with anything while working, on some you can alter the float level if you are heavy handed with it.

Some insist you fit a rebuild kit, never understood why, if it ran fine before dirt got in, it will run fine once the dirt is out, and you have to take lots more bits out of carb to fit a complete kit, so lots more chance of you breaking something, or getting it wrong when you rebuild it.

 

I think it's in the carb also.
If not maybe a valve adjustment.
FYI: your machine is a Kymco. That may help if you ever need parts.