I was running a 44mm lectron for a short time. I was never fully satisfied with how it was performing, always seemed to be robbing the bike's hit/power. Like you, I exclusively ride trails. I put on an OEM 2000 CR250 carburetor (38mm PWK airstriker), and changed the jetting and needle. Been running absolutely clean and perfect ever since. You can't go wrong with the 38mm airstriker. I ended up buying two of them (one for my cr500af, and one for my kx500af). Here's the honda part #: 16100-KZ3-J21. I ordered mine from partzilla, they're about the cheapest I've seen.