Try mixing your oil at 32:1 like the other guys said I mix mine 50:1 Amsiol gonna try 100:1 for MX this year.Anyway make sure the air filter is clean and check the choke plunger/needle make sure the seals are good otherwise it can bleed fuel through choking your motor,mine did.If all thats in good shape then play with your air screw,needle and pilot jet.

88' 250R mant extras

 

P.S post what kind and heatrange spark plug you are using.

 

OK guys thanks alot for the info. I am mixing 40:1 right now so I will try 50:1 tomorrow when I ride. I dont want it any richer than it is now. I am also having my friend who races moto cross on bikes come over to help me jet it. I think my plug is # 9 heat. Anyways thanks again to everyone.

 

I can't run 9's in mine they foul,I use an NGKB8ES,I don't like the resistor plugs either they seem to foul quicker in my experience.