octane boosters?

The fact that chaning the idle mix helps, is a good indicatorr. However, setting a carb and timing curves requires a lot more effort than turning the idle mixture screws. Sounds like with careful tuning, you can get rid of your issue and run pump fuel. Or if you can't perhaps a local good tuner can do it for you. More than likely, you simply need to replace the step up springs and/or jets/metering rods.