I recently picked up this ds 90 for my kids. It runs ok but seems to have some carb issues. It will usually start pretty easy. Once it starts it will pop through the intake when you give it throttle until it warms up. I have cleaned the carb on it a couple of times already. I noticed some one used tape to block off part of the air intake on the air box. It act like it runs a little better with it blocked off and pops less through the intake. To me it seems like it a little lean. it is sluggish also when its cold until it warms up good. when its cold and you give it full throttle it will bog. Once its warmed up it will go ahead and go. I have pulled the plug and checked the fire and it looks like its firing like it should. The carb is a Walbro and I can't seem to find any parts or rebuild kit for it. It acts like it needs a little larger jet to me.

 

also check the valve clearances

 

Any one have any links or any info on the valve adjustment?

 

Hopfully you get it fixed. I had a buddy that bought a new one for his boy. It spent more time in the shop getting repaired than he did riding it.