This test is from the Suzuki RM250 2003,
but i hope it's usefull for your 2004 as well:
Suzuki RM250
Stock Recommended
Main jet 175 162-175
Needle-clip position N8RH-3rd N3WJ-2nd
Pilot jet 48 STD
Air screw 1.5 1.5-2.0
Slide cutaway 6.5 7.0
Gearing 13/49 13/49-13/50
Baseline: The RM250 is another bike that kicked it up a notch in 2003. The power release isn't really lacking in one particular area; it offers a crisp throttle and an overall ridable power curve. We were basically seeking an exhaust setup that would amplify the stock delivery.
Bill's exhaust and silencer Fit: A- / Overall Rating: B Comments: Since Bill's only runs one mount on its silencer, we would have liked the company to have provided a shorter bolt for the second mount/fender bracket. The power delivery of this pipe is quite robust in the mid but tends to fall off up top and lack a usable overrev. This is a system that works best for supercross-style or very tight courses. If you're a short-shift-style rider, the Bill's may work, but if you like to twist it to the moon, look elsewhere.
DEP pipe and silencer Fit: B / Overall Rating: B+ Comments: The silencer mounts were a little off but they didn't pose any huge problems. The DEP robs Peter to pay Paul slightly by snatching some bottom and moving the entire power curve to the right of the scale. After taking some bottom, the mid hits with some power and just wants to keep going and going. The delivery is smooth and very easy to ride as it revs out. This is a great all-around exhaust that is well suited for fast GP-style tracks or even desert riding.
FMF Factory Fatty with Shorty silencer Fit: A / Overall Rating: B Comments: The Factory didn't prove to offer any measurable gains compared to the FMF standard Fatty. If anything, throttle response was slightly improved at best over the Fatty.
FMF Fatty with Shorty silencer Fit: A / Overall Rating: B Comments: The Fatty dispenses gains over stock but not as meaningfully when lined up against the PC or SST. It's a well-rounded system but doesn't stand out in any single area.
FMF Gnarly with Shorty silencer Fit: A / Overall Rating: B- Comments: As a whole, the Gnarly is a little off-center. The output is somewhat flat and smooth for motocross and tends to fall off on top. This is a system that will shine off-road, however. The power feed should billy goat the bike around on the nastiest trails.
FMF SST with Shorty silencer Fit: A / Overall Rating: B+ Comments: The SST hit pay dirt with the RM250. This system enhances the bottom-end while building horsepower through a very usable and snappy mid. Up top the gains fall slightly but are still stronger than stock. The SST is a great moto exhaust and made the podium as one of the top three picks.
Pro Circuit Works with Factory Sound silencer Fit: A /Overall Rating: A Comments: The PC is a full-on moto setup that likes to be ridden hard and revved. The hit down low is better than stock but only slightly. After that point it builds its ponies rapidly and wants to rev. The hit is very punchy but rider-friendly at the same time. The PC combo turned out to be the number one choice.