I've got an '89 CBR600F which suffers from intermittent power loss at high speeds. Once I reach speeds above 100-110 kph the bike starts to momentarily "lose" power. It feels like the fuel just cuts out for a brief moment (a second at longest) and then kicks back in. This makes it really tough to reach safe highway speeds and maintain them as the bike is constantly surging ahead/dragging behind. It doesn't seem to happen at high revs/lower speeds, only once I'm at highway speeds.

I'm not particularly mechanically inclined, but I took the carbs apart and cleaned the jets, it didn't seem to make a difference.

Thats about as far as I've gotten for troubleshooting, so I'm looking for some input.

What could be causing this?

 

Sounds like fuel starvation at high revs. Could be that the carburettor float height settings are incorrect and shutting the fuel in the bowls too soon, causing fuel starvation. If it was like this when you bought it check these first. Faulty ignition could be playing a part, but if the power comes back once you shut the trottle, it seems to point to lack of fuel at higher revs. Other factors unfortunately could be causing your problem such as faulty fuel pump, wrong size/dirty main jets, blocked/dirty air filter dirty spark plugs/incorrect gap. I'm afraid it is a matter of elimination and I know this isn't what you wanted to hear! Start with the float heights first and go from there. Seek help of a mate if necessary. Let us know how you get on?