After the clean-up try to cut down on the castor content in the fuel, that way you woun`t have to do it again. I have the ASP .90 fourstroke and it is my most used engine and have never had the need for a carbon clean-up. 2-3% castor of the total oil content is enough if you insist on using castor. We run our ASP engines and every other brand too, on synth only and the engines look like new inside and out. I don`t mind if my fuel is a synth/cast blend, the price at the moment of stocking up desides what fuel I buy and lately the synth only have been the least expensive