Did you re-set the top end needle. You should have to....If you richen the pump it makes more pressure...meaning the needle valve must be leaned to get the mixture correct.

The needle valve should be around 1.25 to 1.5 turns open....after a little run time they settle out about 1 to 1-1/8th open....I have one motor that runs at about 1.5 turns...

If you didn't re-set the top end then you have it too rich. The motor has a flat spot in the mixture setting. Its about 1/2 turn where nothing much affects it. Say 1.75 to 1.25 you want to be on the lean side of this dead spot int he mixture or it will be too lean when you pull the motor to idle the raw fuel will put the plug out.

This is the first place I would start.

Next is what fuel, plug and prop are you using?
go to Cool Power 30% heli, OS #F or YS plug and a 16.5-12W APC prop

Troy