Misfire not revving

[Stickymint]

Hi All,
Reposting here see if I can get more responce, I have a 660 Skorpion sport, and it has started to cut out / misfire on me, I went for a good ride one weekend parked it for a week undercover came to go to work on it and got half way to work when it started cutting in and out on me. When I pulled the plug it was very sooty black, i'm guessing from unburnt fuel.
I have had the bike in the workshop and started by stripping the carbs which look clean and jets clear, checked the cv carb rubber and all looks in good condition, no muck in the hidden filter behind the floats either. I have put a new plug in, checked the air filter and box all clean. I have tried a new coil all to no avail. On the petrol front the bike has had several tank fulls go through it and on the ride out the week before she never missed a beat. If i blip the throttle it seems to rev round to the red line ok, but if i slowly build up the revs she starts cutting out about 4500-5000 rpm and wont rev through. HELP getting fed up, need to be out riding it.

[comanche91]

I've had similar problems here in the US although not as drastic as your Scorp sounds like. I'd get mild cutting out under WOT and went through the carb and found nothing wrong. It turned out to be the station where I usually refill switched to 20% Ethanol gasoline, and the old Rotax didn't like it at all. Found a local station with Ethanol-free gas, and after burning off the rest of the Ethanol crap from the tank it runs as new now. Worth the extra pennies/gallon for the Ethanol-free product if it's available in your area.