I found a big help to keeping the tips clean longer is to always use a top tier gas in my car. I use Shell in my n/a & go many months before there is even a light haze that might be appearing. Most of time I have to run my finger across the i/s of the tip to really notice the slightest gray coating building up. I went to a neighboring state on a weekend trip a while back & there ETHANOL is way of life in most of their fuel. Sure enough after the 300 mile return run I immediately noticed a dark gray build up from the out of state fuel. Have used my top tier since I'm back & no more build up on my exh. tips.