Daniel Foley

Hey everyone, I am new to this forum, and I am new to owning a DT and so far I have had a nightmare with the bike. I brought the bike of someone for a good price, and the bike look well presented, and well looked after. The bike is a 1995 DT125 and has done about 11,000 miles. The problem I am currently suffering is that the bike accelerates OK, but when it hits the power valve the engine makes the sound of the sudden power increase but there is no noticeable power increase. I thought that it would be the clutch plates but there was no clutch slip 2 days ago before this problem? A few days ago the bike overheated and one of the radiator pipes had been loose so it blew all of the coolant out of the engine, after that, came the powervalve problem. Before the overheating problem, the bike is extremely sluggish before the powervalve, however if its given enough revs it does pick up, I am at my knees with this bike, I have tried everything, but it seems the person who previously rebuilt this didn't do a very good job? It had a new piston and rings on its last rebuild, or so im told. I brought the bike, wish I had looked it over more. So my questions are, Why would it make the sound of the powervalve opening without giving the power? I took the powervalve casing off, and the middle of the valve bush just spins around, is it supposed to move when its at high revs to open and then return back to being closed? When I rev it, the thing just seems to move based on vibration? it can spin all the way round? Why is the bike sluggish at low revs? (We have checked the carb, seems to be very clean, although at the very top one of the screws had sheered off leaving half the screw in the top and a small gap, which we have plugged with rubber gasket sealant, would this impact also? Oh and the bike has a flat battery, If anyone can advise that would be great, if someone could also give us an idea of how the powervalve should work/ be setup that would also be great, Cheers Daniel