The truck carb may very well have bigger jets, but the only way to tell would be to remove the tops of both carbs and compare the jets. The truck carb may also give the engine a bigger squirt of gas from the accelerator pump. It might not hurt to check the plugs to see if the engine is getting the proper air/gas ratio, indicated by a light tan color on the porcelain. This is best done with new plugs. And finally, have you checked for any gas leaks?