I have converted a st g90 to gas with a carb adapter from mr lambert, has a walbro carb, the problem i have is the engine idles and transition is great to mid where engine runs great but as soon as you make it to say 3/4 power it starts to surge and will just keep on surging till you bring the power back to bout half where it will run great again.

Any thoughts as to what this might be? Any advice on approx needle settings or potential problems with these gas conversions?