Hi Rotax-Owner.
I am attempting to synchronize the carbs on my RV-12 again (912 ULS). I decided the CarbMate is not that great and I picked up a set of mechanical dial gauges. I like them a lot more. However, I'm experiencing a rather frustrating thing that I also experienced with my CarbMate, which is that over the range of the throttle, the synchronization changes. If I set it up so that I'm synced at 2500 RPM, it's off when I run it up to cruise RPM. If I set it up so that I'm synced at cruise, it's off at 2500. I can feel it, and so I believe the tools, and as I said, both the CarbMate and the mechanical dial gauges agree that this is happening.
The carbs were recently overhauled (using 889 534 overhaul kit), as well as new choke innards, new carb pistons, the works. Everything including the kitchen sink was replaced in them. In hindsight, I would have just bought new carbs to begin with, but it is what it is.
After finding this potentially dubious behavior to begin with, I took the carbs off twice now and reinspected them to make sure everything is assembled correctly. I have found no issues, and I've been very careful.
The air filters were recently cleaned and re-oiled. The carb sockets are brand new and tightened properly down to the spacers, and they are snug. The carbs are fully seated in the sockets.
One thing that seems a bit awry is that when I perform the carb sync procedure in accordance with the RV-12 MM, after doing the mechanical synchronization and starting the engine, the full idle position is about 2500 rpm cold and goes up to about 2600 once warm. This is waaaay high obviously. The RV-12 MM says not to back the idle screws off more than 1/2 turn to achieve on-idle synchronization. It's a bit ambiguous in the wording whether it is acceptable to go past 1/2 turn to set the idle speed after the idle is synchronized, but it needs a full turn to be close to 1800 ish, and a little further to get it where I want my idle stop to be, around 1650. Not sure if this is fairly normal on RV-12, but I would not expect it to be so far off to start with.
The idle stops do not appear to be bent / damaged.
Any ideas as to what might be going on here? The RV-12 throttle setup uses a different spring than the default Rotax throttle return spring, and it springs to full open and is pulled to idle by the throttle cable. The RV-12 throttle arm setup is a bit different than the default 912 setup.
I expect that perhaps the first thing anyone reading this will suggest is the carbs themselves. I've been pretty thorough with those, I do not think the issue is there. Could be, but I don't think so.
Another possibility is that this behavior is completely within "normal" and I'm being too picky? It's not grossly off. But it is noticeable.
Unfortunately, I do not know whether this was occurring before the carbs were worked on.
Your thoughts are appreciated.
LSRM-A
Rotax iRMT Heavy Maintenance
RV-12 SLSA Owner