spark plugg are burnt

Check the plugs to see if they are the right type and heat range for the engine. They could be too hot a range of plug and were put in the non-foulers to keep them cooler and not burn up. Or maybe they were the wrong types with too long an electrode and someone put them into the non-foulers to keep them from hitting the pistons...people have done dumber things!

OK, sounds like oil fouling is not the issue. Yeah at this point I would put in a set of inexpensive plugs as suggested and make sure they are the right type (don't just buy the same part number!) , turn the engine over by hand as you put in each plug to make sure they clear the piston tops, and see how it works. If it runs good, take them out at intervals for while to see how they are doing.

And one other thing: maybe find the head part number and look it up to see for sure what year it is (or ask here), and match the plugs to the head.....who knows what head/block comboe you have.