A tear down would be the best thing to do. I got sand in one of my engines and couldnt remove the conrod from the crankshaft so I opened it up as much as I could and flushed it out. I must have flushed about half a liter of fuel through it. I never did get everything out, I could still hear a little grinding. 6 gallons later and it runs great, cant say that will be the case for you though, thats why I say a complete tear down would be the best.