DT125R FORUM

@Calum as you know, DTR was first released in 1988 and even though YEIS has been a part of the intake system on the DTR throughout the years doesn't mean it did very much for the performance in either way. And because YEIS wasn't implemented in any newer two-stroke models from Yamaha may confirm that. YEIS might also have been more of a marketing strategy to keep two-strokes popular in a time when four-stroke engines began to take bigger market shares.
Yes, Yamaha could have removed it, but that cost resources and money. So why change something that probably just doesn't matter either way? Yamaha is also a company that are reluctant to change motorcycle models that still sell well, like the DTR. Yamaha YZF ThunderCat was another motorcycle that was sold for many years virtually unchanged. In Asia and South-America there are models designed in the 70s that still are produced and still sell well in those markets. They aren't even manufactured in Japan. Actually, Yamaha has a lot of factories around the world that produce the same models year after year, and models we will never see in Europe or the US. Even the design of some models is done outside Japan. I know for sure that Yamaha DTR 50 was designed and produced by MBK in France, not Japan.

The idea of Yamaha's "Yamaha Energy Induction System" (YEIS) was developed in the early eighties to comply with the new exhaust emission standards in the US at that time.
In theory, the idea was to conserve some of the air momentum via this box and help fill the crankcase at the next stroke. Yamaha claimed this had an effect on both fuel efficiency and power. But it was later discontinued and I can't remember that any other motorcycle brands did something similar.

@Deltadeano I have the same DTR as in the first picture. Black with grey/red pattern.
Ordered decals from Ebay. About £30-40 for a complete set. Didn't expect it to be like original, but it was not even close to the real thing. Color didn't match and fit was a bit off. Also, I got a few air bubbles, but that I can blame myself for, I guess.

@Arild Isn't Sweden an EU-country? I live in Norway and there are virtually no extra fees ordering from China or other countries, at least when ordering stuff worth less than 300NOK (about £25). And Norway isn't even EU. That's strange.

But you could try to search for hobby stores in Sweden at the web. Some stores might have a 385 motor. As I mentioned, it's an ordinary hobby motor.

@GeirA said in Ypvs servo motor:

The YPVS is quite simple a servo motor that works just like model airplane servos. As far as I know, the YPVS use 12V supply voltage and 4,9V PWM pulse signal.

I have researched a bit more and found that I have mistaken the pulse signal for being PWM. It's probably the rpm signal, not PWM.

These motors are simple DC 385 motors and cost next to nothing from sites like AliExpress, Ebay and Amazon.
Just Google "385 DC motor" and you will get a lot of hits. They usually come with different voltage and rpm-ratings. So buy a few and try which one works the best. It should also be fairly easy to work out the rpms too by doing some simple math.

Please post which motor that worked best

The YPVS is quite simple a servo motor that works just like model airplane servos. As far as I know, the YPVS use 12V supply voltage and 4,9V PWM pulse signal.