GT valve float problem

[sdinf99]

I have an odd valve float problem (or normal I'm not sure). It only happens at high speed (70-90mph). The car looses power momentarily with all the symptoms of a redline, then it's fine. You can slowly creep up another 5/10 mph then it happens again (happens with revs around 4.5-5.5k). It doesn't happen in 1st or 2nd but figured that might be because the cam rotation speed is higher in lower gears and the valve float is less a problem??? In case it's relevent, the engine overheated before I bought it (cheap) and I had to strip the head down to clean all the congealed oil out of it. I've replaced the head gasket, the head has tested flat and there is no water getting into the engine/oil or loss of compression. The timing is also spot on. I know that springs can be damaged by excessive heat and am intending to replace them but at £138 for 16 springs I thought I would check if there was anything else that could be causing this problem before I do.

Also does anyone know where to get 16 valve springs cheaper than £138 in the UK?

Any advice would be appreciated.
Cheers

[Pineapple]

If the valves float, it won't matter what gear/speed you're in. They'll float above a certain RPM.

[tankd0g]

It's probably something a little simpler like plug wires. I can't see valves floating at that rpm luness you rebuilt the head with the wrong springs.

[sdinf99]

Thanks for the replies, I didn't get as far as taking the valve springs out, only cleaning the shims and lifters. Will try another set of leads though. Any other thoughts would be appreciated.

Cheers