Jabiru have had one overriding principle - to keep aviation affordable for the average person and for this they have been extremely successful. But the tradeoff is that some components have to take the middle of the road design.
The propellor is a major example. The kit uses a "Jabiru" prop made by their own supplier. It is a single piece laminated timber prop with epoxy and fibreglass skin. It has a leading edge black epoxy protector strip.
I have now used three props and have had lots of dealings with the two other users of jabiru engines and props in my home city (plus contacts with a number of other users).
Universally we all agree that the prop design is too coarse in pitch for the engine. I have used two jabiru props and in none of mine nor the other two in town have we been able to get the full static RPM that the manual requires.
The manual states you should get 2800 - 2900 RPM on full power on the ground standing still. We have never got any of our RPMs above 2700 (except with my new prop which is not a Jabiru prop)
The problem of too coarse a prop is that you don't get as good climb performance. But you get better cruise speed. Because it is a more drag loaded weight on the engine you tend to use more power to drive the prop to get your "book value" RPMs. So you use more fuel. If it is in the "right" compromise area it's OK, but even a little too far either side of compromise and it takes on too much of the unwanted characteristics.
I am currently using a Sensenich prop which gives me 2850 but I can take it off and reinstall my Jabiru prop and only get 2620 RPM.
I went through lots of angst originally thinking I had an engine problem and even unhelpful multiple discussions with the Jabiru engine shop. Jabiru were a bit defensive about it at first telling me that my RPM gauge must be wrong (all three of them even though they were all reading the same!) but they finally came to the same opinion and sent me a used finer pitched sensenich prop (my current prop) to try out to see if it fixed the problem. Which it did. We are very soon going to have to start talking about what we do (read "who pays for what" ) about the long term plans for a finer pitched prop. I'll keep you posted on that.
So what to do if you have the same problem?
So long as it's not too low you could just accept the lower RPM. I was willing to accept the 2670 to 2700 I got on my first prop because it still climbed well and fast in the cruise but I was not willing to do so on the 2620 I was getting on my second prop (after the repairs from a prop strike). I found it just didn't want to climb like the original. It got good speed in the cruise but used up lots more fuel trying to spin the heavier load. I would be worried about take offs if I operated at max weight all the time.
I know of another guy locally who resorted to getting his prop repitched by a local prop guru.
There is something that can be done which may add some RPM. I added about 40 - 50 RPM to my original by cleaning up the profile of the leading edge black edge protector.
The above mentioned prop guru looked at my prop one day and casually mentioned that I could probably get more RPM just by smoothing out the trailing edge of the protector so it was flush with the timber. I didn't think it could make that much difference but did it anyway - as I was below the supposed "proper" static RPM. I was surprised how it added nearly 50 RPM.
It goes without saying that you have to keep the blade clean, smooth (repair nicks straight away) and properly tracking. I always do my run ups on the move on airfields with stones gravel and stuff so I minimize the risk of stone damage.
You could replace the prop with another brand - I can only speak for this sensenich prop and it is really nice. "Climbs like a homesick angel" as the prop guru says and its cruise speed is barely noticibly less than my original. But that could be an expensive excercise.
Lastly you can wait around a bit and watch the Jabiru website. The current word is they are developing a composite three part (hub and two blades) ground-adjustable pitch propellor. The cost (apparently ) of composites has now dropped enough that it is a viable alternative to the timber one with the added advantage that adjustability can be added.