rough mid-range and carb questions

Thanks for all the great info Trond.   I'd like to run an airbox, but my installation is pretty tight, so there's no room for the stock unit.  I bought a used one to see if it could be made to fit, but I think eventually I'll have to just build a custom airbox.  So far, I've only run separate filters, using warm air inside the cowl rather than an external inlet. Another variable here that I mentioned before is that it got colder between the time I started the cylinder installation, and the time I finished, so that would have an effect on mixture as well.

The carb rebuild kits will be here around mid-week, but I don't see any reason not to try changing the needle settings first.  I really don't want to completely rebuild the carbs yet, so if something that simple can resolve the issue, I'm all for it.  If not, then no real harm done.  I'll start preparing my custom screwdriver for those pesky needle retaining screws. 

Ultimately, I'd like to move to fuel injection, and I have everything I'd need to experiment with a custom EFI installation.  The idea was to do this on the ancient engine I have on a test stand first.  Sadly, that project hasn't started yet.  I do have a wideband AFR unit that would ultimately be an input to the EFI computer, but I might think about setting it up to work as a portable unit, then clip the sensor inside the exhaust pipe for ground testing.  I use the Toucan exhaust though, so I'd be sensing one side at a time.     

Thanks,

Rusty

use heat on that needle retaining screw, untll there  is a tiny puff of smoke from the Locktite. 

Also I ordered my new needle jets from Bing. Stock for the 912UL is 2.72mm and I ordered the two next steps up 2.74 and 2.76 because it takes so long to get them to where I live

I had one hour today between showers, and engine runs good. I pull full choke on cruise to keep AFR below 15 and that works too

I had air filter cones /"pods" on my last Rotax 912ULS - worked perfectly for the 10-12 years/920 hrs, I had the aircraft. 

I did checked out the inlet air temperature, over several weeks, - consistent 10C above ambient.

Didn't have icing protection and as far as I know never had an icing problem.

Considered trying to get fresh/cooler air to the carby's but figured the minute improvement in performance would probably be at the cost of potential icing  - so left well alone.

If you changed out the 80hp piston’s with larger 100hp pistons you are pumping more air that requires more fuel than your stock 80hp carbs can provide. Changing jet’s to the size used by a ULS would probably help.

Oddly, the main jet for the ULS is listed as 155 and the UL is 158.  This seems completely backwards to me.  When looking at airboxes, I did note that if you add an airbox to the UL you're supposed to change from 158 to 155.  I did buy the 155 main jets, but was advised to just run it as is first, and adjust if the EGTs indicated the need to change jets.  EGTs in cruise are 1400-1450 which seems fine to me.  From what I read, I believe the UL and ULS needles and settings are the same.

Thanks,

Rusty