My smaller STs (.29, .51) throttled awesome on 5% - they even throttled nicely on straight fuel. The S90 was the picky one of the bunch. For the first few gallons, it needed the spraybar clocked 45* from straight in (fuel nipple pointed at rearmost hold of mount lug); after that third gallon of fuel or so, it was like a light switch went on and the engine ran horribly lean in the midrange. Reset the spraybar to straight in and it throttled like the .29 and .51 on the usual 5%/20% brew I used. Last summer I tried 10% in the .29 and it ran okay on it (on a full tuned pipe no less), the .51 & .45 may do fine on it as well, but the .90 will stay on 5%, especially with the new ring in it. When I was breaking in the .90 on the factory ring, it would barely tolerate 5% nitro. It seemed to be the pickiest of my Tigres.