Does anyone have suggestions re: power enhancements for my Expedition 425?
i.e. exhaust, carburator, jetting, air filter, etc.
I'm looking for more "external" add-ons...not being a mechanic I'm not inquiring about which cam, valves or lifters to use.
Thanks.

 

The H.O. treatment works pretty well to wake up the EXP. The motor is basically the same as the Sportsman and Scrambler. The cylinder heads and cams are the same part number. I put a H.O. cam, and intake manifold on ours with a 38mm TM Flatslide Mikuni (no accelerator pump, but not a TMX, which is for 2-strokes) which I got from AAEN. I also opened up the exhaust a little with a torch. It runs dead even with my H.O. Sportsman in drag race after drag race. The smaller displacement is offset by my son's lighter weight.
I know you didn't ask for cam info but thought you ought to know. Swapping cams is easy.
First time took me 3 hours just goofing around. I can do it in a little over an hour now. You don't pull the tank or anything but the side panels and covers on the cylinder. A shop should not charge more than 2 hours for swapping a cam and carb/manifold. Jetting is another issue. If you can jet it yourself the H.O. treatment wouldn't be that expensive. And Nothing else works, by the way. That Fugi 4-stroke gets up to H.O. and hits a brick wall. It just doesn't go past that without a lot of work and money.
The limiting factor on the EXP becomes the rev limiter, which I never figured out how to defeat. The Scrambler guys figured out it's the orange/grey wire but on the EXP that controls the reverse solenoid.
I have an extra H.O. cam I will sell for $125 including shipping. It came out of my H.O.
which has a AAEN long duration cam. It does nothing for $259. But it is in so I'm leaving it.
Lots of Luck, the EXP is a great machine, but not as great as a Sportsman. I think it actually slides a little better due to more weight on the front end/motor sits farther forward. And a Sp jumps better for the same reason. It is a worthy steed, one of the best trannys around, and definetly one of the "Big Dogs" especially with the H.O. treatment.