97 Harley Davidson 1340 fouling plugs while running

Are the plugs the right brand and heat range for your Harley? Also, check the plug gap. Try to read the plugs; i.e. is the fouling caused by oil, incorrect carburation, metallic oxides, etc. Next, I would check the engine's timing. If nothing is funky, you may need "hotter" running plugs. If the plugs are fouling due to oil, the engine likely needs to be rebuilt.