JH600 Valve Problem

[Lao Jia Hou]

The "valve problem" turns out to be an automatic decompressor problem, right?

Yes, that is my understanding.

These are the facts we have observed at the gasstation:
1. Up to the stop at the gasstation the JH600 ran fine. I asked my wife if she had observed some misbehaviour, anything. She reported nothing special was noted by here when driving all day.
2. When she turned off the engine, she did not hear anyting unusual.
3. When she started the engine again, I was in front of her and I could here the startmotor, the click of the engine starting mechanism and I heard some tickling noises which were never there when the engine started before.
4. However, when it started, it idles at ca. 1800 revs/min.
4. Very carefully opening the gas did increase the revs/min. but at ca. 2.500 revs/min. the engine suddenly dies and stops. Consistently.
5. When turning off the engine, one has to hear a quite loud click just before the engine is silent, there are now two (!) states:
5A. There is the loud click
5B. There is NO click at all.
6. When state 5A is present, the engine can be started again. However, the strange tickling noise is present just after the engine started and then this strange noise vanishes.
7. When state 5B is present, the engine starting motor can not start the engine. It does not turn the crankshaft over, one hears that the startmotor tries, but the power is insufficient and the lights dim a lot.
8. The battery is 100% OK and fully charged.
9. For both states 5A and 5B the engine can not be reved up anymore past 2.500 - 3.000 revs. It always dies in this range.
10. Driving is impossible and we had to leave the JH600 behind at the gasstation and pick it up in the coming days.[/SIZE]

Prior to my "B" getting a new decompressor assembly (reference the stalling issue thread), when I turned the bike off, there would be a noticeable "clunk" from the engine. There was also excess engine noise (not really a ticking, per se, but more like a "loose" valve train). I think Motokai had a highly noticeable ticking. My "clunk" and "noise" seems to have disappeared after the decompressor/cam replacement.

It is very interesting that it appears the JH600's starter does not have enough "ooomph" to turn over the single cylinder unless the decompressor is activated, if that is what is happening in your case (i.e., decompressor is NOT activated, therefore not allowing the starter to turn the engine over). Presumably, that is the theory behind the decompressor - release some of the compression to permit the low-power starter to turn over the engine.

BUT ... why would it die again at around 2500 RPM?

I think the theory is that the auto decompressor retracts from centrifugal force when the engine rotates over a few hundred RPM. Maybe yours is not? And maybe it is re-engaging at that higher RPM?

You say that it now idles at 1800 RPM ... what was the idle before this issue arose?

Really sorry to hear about getting a new bike stranded, far from home. Well, at least you speak the language!