I've had this jug sitting around for months. Today was the day, figured I might as well throw it on just for kicks. The exhaust port is much higher than the DT360, by about 6mm. This moves the power band up quite a bit and takes a pretty good bite out of the bottom end and midrange torque. Not what I was looking for but you never know. Sometimes the results of these little experiments are unpredictable. The MX360 head uses a much smaller dome with a modern hemispherical shape and reasonable squish band width so I was hoping that may offset the hit to bottom end power.

The DT360 jug pulls well off the bottom, torque ramps up toward 4000 RPM and the pipe comes on around 5000 RPM and pulls through 7000. No dips in the power delivery. The MX360 is flat down low, soft in the middle and doesn't really get going until about 6000 RPM. Once it comes on it pulls strongly through 8000 RPM, exactly how far I don't know because I try to shift by that point in the interest of preserving the bottom end. I don't know how well suited the stock big end bearing is for 9000 RPM running, don't want to push my luck. If you short shift though you fall off of the power into a bit of a hole around 5500 RPM.

Overall I like the DT360 cylinder better. The MX360 is faster if you don't mind winding it way out but as expected, it just doesn't do much in the low-mid.

Did you run the MX head with the cylinder or the low compression DT360 head. I guess you used the right head or it would flatter than flat at low revs. The MX pipe would top it off compared to the restrictive DT pipe. Sounds like fun though experimenting.

Did you change your ignition timing they both run different timing

Yeah, the whole lot was MX parts. Head, cylinder, pipe. 35mm carb, which is slightly bigger than the stock MX carb I think.

The DT setting is slightly advanced from the MX setting. I didn't change it from where I had it for the DT parts. This thing is running a Rex's race kit with the advance/retard ignition curve so I figured it was close enough. It didn't ping so if anything I could have run more timing.

More timing helps the low-mid power quite a bit. RT180 CDI box has a curve that makes a noticeable difference in low-mid power compared to running a "static timed" points or early CDI.

Timing needs to be retarded on a two stroke at higher RPM. Notice how Yamaha retards it back down to 15 degrees... Most fixed timing ignitions are set about 20 degrees... a compromise between good low-midrange and higher RPM. More timing than 20 in the low-mid rpm and less at higher rpm is better.

Yeah I would play with the timing a bit for a happy medium. Is it the dt piston too I'm guessing. When I did the mx porting on my dt250 I cut and drilled the piston as well due to them being different on mx250 cut the bottom of the inlet side skirt off and added an extra 17mm hole to give it 360 degree inlet timing also had to trim both sides under the gudgeon pin bosses to match the transfer ports

I was already running more timing than the stock MX spec. The root of the problem is 190 degrees of exhaust port duration. The port is about 6mm higher than the DT, which is huge. I could understand maybe half that, if you were to split the difference between the MX and the DT you would end up with about 180 degrees. That's a far more appropriate amount of exhaust timing for a large displacement single cylinder engine.

Don't get me wrong, the power on top was all there but down low, with tall gearing for the street, it was just too soft. Running a 16T countershaft sprocket it was unable to maintain 50 MPH up a mild incline without downshifting to fourth gear. It was well behaved. Very smooth, clean carburetion. The extra 2mm of transfer port timing seems to help mitigate the effect of the extra large case volume. It just sucks having to wind it up to within 1000 RPM of the DT redline before it starts moving out.

I did run it with a drilled and trimmed 81mm piston. 360 degree inlet period, trimmed back the skirt on the exhaust side to minimize shrouding the transfer port entry. I also opened up the intake port just enough to stuff the KX reed block that I have been using on the ported DT jug. It is slightly larger and uses carbon fiber petals. The bottom end and midrange would have been even worse if not for that.

After my curiosity was satiated I swapped the DT top end back on. If I want to explore the red zone on a tachometer I'll ride my 250. That thing is more than happy to spin up to 9000 RPM, though the gear ratios are close enough that it's not necessary to wind it all the way out to pull the next gear.