Again, if you don't set your timing (BTDC), it's not going to run or if it does it's not going to run right. The dude in the video kept saying TDC, that's not correct and his bike ran like crap, wouldn't rev. Here's a quote from the Vape instructions, they don't tell you where your BTDC should be but if you read it carefully they do tell you to set it.

"Remove the spark plugs. Place the rotor loosely onto the crank and check that it may move freely above the statorbase. Bring the piston into ignition position. Put the new rotor handtight on the crank shaft for turning the shaft."

NOTE: look at where they say "bring the piston into ignition position."

I could be full of it (I"m not as smart as many on here), but I did install a Vape on my DT400, setting the BTDC correctly then lining up the marks and it runs fantastic - better than the stock setup!

Thanks for the responses, especially for the BTDC which I confirm I have mounted correctly (1.8mm).
As for the carburetor I don't remember why I got it so small, I think I read somewhere that it could fit. In truth I would question the size of the carburetor if the bike never started...but it did start...even on the first kick of the times....e would stay on.
Only as soon as I opened the throttle the bike struggled tremendously and didn't respond well, so I thought the carburetion was too lean and increased the jets...hence the first problems. I returned everything to normal settings, cleaned everything (carb. and piston), checked spark plug and gasoline....but nothing.
There is to say that when I opened the engine to get to the piston head the same was REALLY dirty...all black....symptom of too fat carburetion...
So I decreased the jets (only a few points), but to no avail.

I, too, thought I had to set it on the BTDC, and so I did, and the bike started just fine.
Thank you very much for the explanation, one less hypothetical cause of the problem to check

I chose this size because it was easier to fit the manifold I made with a 3D printer, and even in terms of size it is very small and unobtrusive. I also wanted to have the ability to have all the different jets (minimum and maximum) so I could set the carburetion as I wanted. Rightly you could say to me "yes but with the same measurements there is also the 21 one" and you are right....but the bike started....so as you say there is no reason why it doesn't work

Not easy i guess to keep the motor sitting at 1.8 while fitting the flywheel. Be good if somehow you could lock it there while fitting the flywheel especially if you might need to fit it by hand & remove a couple of times to get it perfect on the line. Also to stop any chance of it moving while starting to tighten the nut. Be interesting to strobe it running & see how things line up while running, or if it alters the timing with revs by magic built into the system.

Sorry, think i was writing above on page one above haha, not sure if still appropriate.

Hey Morley, hope you're doing well down under...  I found/figured out on my DT400 that all I had to do was get the marks lined up close then I can loosen the stator to line up the marks.  Figured that out after many frustrating times trying to tighten the flywheel down only to have my timing move on me

Good point 'that', providing the screws are fully accessible with flywheel on & sort of looks like it albeit slightly shrouded in the pic. Sopme of the pics in the link are a bit sus & not related to the system OP is using--i think.

The screws on mine are barley reachable but doable, they are countersunk allen head so that made it easy to get the allen wrench in.

I actually had the same thought but when I saw that it started without any problems, I told myself I had done a good job. It is not easy, but more or less you do it. There is also to be said that they are relatively "simple" bikes and just the VAPE system alone helps a lot. In the end they are tractors....I understand that it's better to do the work to the tenth of a millimeter, but if we think about what they were designed for...I guess a tolerance gap is there.