I have a running problem I can,t figure out. A new km 5 b less than 6 months old came with a 668 carb, it ran fair. ( hard to fine tune) so I bought a new walbro 990.and put on a new aluminum insulator with Teflon gaskets. It ran great for a couple of weeks and out of the blue it runs crappy. I can,t tune and find the sweet spot. I have spark, it starts , it runs. I started at factory settings but it wants to bog out and any adjustments don,t seem to help. I use castor 990' 25/1 mix and it has a silenced tuned pipe. And I noticed a little fuel in the air filter housing, is this a ring problem? I,m open for any ideas. Thanks