Having taken my DT2 250 out on weekend rides, I've found that the top speed im able to achieve is a slow and steady climb from 40mph to reach 50mph in 5th gear and throttle fully open. The fastest I've gotten to was 55mph, but that was going down a steady decline.

The cylinder was recently bored to the first oversize and fit with the appropriate resized piston/rings.
I'm running a 1/4" inline filter fuel filter, which I suspect is hindering the top speed, but are there any other adjustments that I may be overlooking that could help with the top speed?
 

Yeah.That's pretty slow for a DT250. 1st things i would check is your exhaust for restrictions (plugged up) and check your timing. Be sure you have good points in the bike. Maybe a restricted air filter too? But you would notice this because the engine would not rev out clean? It would be sputtering. 

Yep i'm still stuck in exhaust mode too for anything lacking performance.
Also timing like SKYDANCER46 says.
Check the points gap through the slot to see if they look like they're opening to an eyeball 15 thou or barely moving open.

Check the spark arrester is not blocked its inside the exhaust behind the baffle

After you get your basic issue sorted out and you still want alot better performance , give me a call , 702-858-9177

Rich

My first thought was exhaust same as Morley (RT325) and Skydancer but then I remember when I first got my DT2 up and running I didn't tighten the points good enough and it developed a lack of power like yours.

I put a plumbers torch to the end of the exhaust and used a thin spiraled wire brush to scrub the inlets of the exit end. It loosened a good amount of carbon which came out as flakes and soot. Taking it for a ride after that I did notice a bit of a difference in responsiveness and was able to get to 55mph on a flat straightaway, which I wasn’t able to do before.

I read on another forum post , suggesting you can plug the tail end of the exhaust, fill it up with about 2 cans of oven cleaner, let it sit for 24 hours, then rinse with boiling water, let it dry or dry with a heat gun then.

Would leaving oven cleaner to soak for 24hrs inside of the exhaust damage anything within? I did read that oven cleaner can damage aluminum and wanted to check if anybody knew whether there was aluminum in the exhaust of this particular model? Also has anybody tried this technique with any success?


Thanks!

Putting the exhaust on a bonfire will work. Just be careful it doesnt get too hot and melt.

No aluminum in 72 pipe. 

Rick C?...  he's an accomplished restorer who has built show-winning bikes.  I haven't tried that exact method but if he says it works I believe him.

I also burn in a fire pit but I have used easy off yellow for carbon buildup before