Das finde ich auch merkwürdig.
Die Schaltpunkte sind zu spät, jedenfalls für die Strassenverhältnisse Europas. Wie es auf ner algerischen Sandpiste zu fahren ist, weiss ich nicht. Ich kann mir aber vorstellen, dass man dann rausholt was drin ist, besonders wenn der Motor so schwach zieht, dass man nicht über 100km/h kommt.
@terios: There is enough Space to work.
You can measure the shims, but to replace them, the camshaft has to be taken out.
Kokomiko (and me too) are astonished about how late you are upshifting. At 30km/h, he would shift into 3rd gear already. Further, Kokomiko asks, if valve clearence was never checked before.
If no, that alone would not be alarming to me, but in combination with the high revolutions driving you obviously do, it could be at high time to check valve clearance.
You can find tons of pictures from inside that engine here:
http://www.daihatsu-forum.de/vbullet...benringe+rotzi
That is a tread, where our higly estimated user Rotzi documented a piston rings replacement, and he ended up in a more or less full engine restoration.
An Idea from myself: Did you check if the fuel pressure is ok? Because once, when I had a weak fuel pump, I noticed a slowly increasing lack of power too... but that would not explain the engine noise.
Is the engine running smoothly, or is it bucking? If it doesn't run smootly, I'd try a replacement of the spark plugs... but this is for sure not the reason of the noise from the Engine too.