Has anyone upgraded their 1974 dt250 to a Rex’s speed shop 12 volt kit?  The actual kit is a RMK6-12 volt. I’m having a heck of a time getting this thing timed. I have the timing light on it and it is about perfect no matter how much I rotate the stator. Rex suggested rotating it 1mm at a time which I did. The bike will run and idle fine. At 5500 rpm it starts to cut out. Was running fine before I put the kit on it. It has always been finicky with timing but I can’t seem to find the sweet spot this time. Any help will be much appreciated. 

Just my random thoughts & timing isn't an exact science as regards misfiring at 5500rpm. I think you might be looking for the wrong cause but happy to be proven wrong. You say "was running fine before fitting the kit" so is there a wiring fault the way they're connected. I live in the past--& still have points ignition. I won't say exhaust or carb because was ok on original mag--but i'll say it anyway lol.

Thank for the advice RT325. I 100% agree with you about it possibly being the carb or something other than the timing. I’m going to take the kit off this weekend and put the points back on it to test my theory. These are old machines so it is quite possible something else broke during the change out. Almost sounds like the pipe is clogged but I had one of the guys on the site make it a “sleeper” pipe a few years ago. It could be plugged I guess. Changing back to stock will verify. 

So what happened?

I fitted a Rex kit RMK-8 6v to my bog standard DT360a, this is the standard 6v kit, but it wouldn’t rev past 6150rpm in any gear.
I contacted Rex, they sent me a kit RMK-17 V5, when it was fitted, the bike wouldn’t rev past 4500 and would cough and splutter at that point.
I refitted the RMK-8 and again it wouldn’t rev beyond 6150.
Timing on mine is spot on, crank seals fine, compression 150psi, NOS exhaust, new air filter, carb setting standard, good colour spark plug.
Given this experience, I think the causes of mine and yours lie within the Rex kits.

My 360 has not rev past about 6000 in gear since new.

It sounds like the kits are duds for some reason. The build quality is nice in the metal components. Not sure what is holding it back?  I haven’t had a chance to go back to stock. My weekends got busy with other projects. On top of that I already changed out all the light bulbs which takes a minute to do. Really hate going back to stock since the new headlight is worth the upgrade itself. You can see at night!

I was really hoping that it was something silly that I was overlooking. Sounds like it isn’t. I upgraded originally because my 6 volt system would short out with even a mist on the road. I’ve been caught out a few times when a rogue shower shower hits and then I’m dead on the side of the road until everything dries out.