yes, it was only two stuck pistonrings. Probably because the engine had not been running for over a year. Two new pistongrings and cleaning gave us a well running engine .
Again thanks evrybody foor the advices!
Koos

Thanks again for all the usefull information.
We sadly had to come to the conclusion that the lack of rpm is due to worn pistons and rings.
We now are going to take the engine apart and see if we are right..
Koos

Today we tested the engine with the original gearbox and prop and, like was to be expected, the rpm is much higher now. But now the engine seems to get not enough fuel to reach the 6000 rpm. It runs well untill 4000 rpm. but when excelerating it does not get quick enough in the higher rpm area.It on...

Hi Koos, do not take this personally. I might be wrong but from your questions and answers I get the feeling that you might not be qualified to do this whole process by yourself. I do not think you need to change the gearbox, rather look at a prop to fit the gearbox you have. This process could cos...

Hi guys,
Thanks for all the help. Tomorrow we will change the gearboxes, because that makes the most sense now.
i'll let you know the outcome. keep my fingers crossed
Koos

Well, I found out that the new gearbox has an other ratio than the original ( 3,47:1 instead of 4,0 :1) which is a difference of about 12.5%. Could this explain the lower Rpm? And if so, what would be a wiser thing to do: Change the gearboxes or adjust the propellor angle. I have got a 3 blade prop ...

I do not exactly know yet. From your question I understand that it could be the reason for the low rpm. I will check out which gearbox is on the engine. If it is an other type than on the old engine, the problem might be solved if i change the gearboxes. To day i am going back to the airfield and fi...

I obtained a used Rotax 582 engine ( has run 300 hrs) to replace my old engine that had a seizure. After rebuilding the engine on the frame of my cosmos trike, it started well and runs smoothly. The only problem is that it does not get more than about 4000 Rpm. The engine comes from a zeppelin in ge...