Running 912 without prop

[egp8111 7]

I'm running out of ideas to get a 912 to run smoothly between idle and 3000 rpm. I've tried all the recommended solutions. I've had the carbs off and apart some many times I'm about to wear out the screws! I've synced it to perfection but it still runs rough between idle and 3000 rpm. So now After reading on line I'm thinking maybe the gearbox is out of spec and needs rebuild. But before I go to the trouble of pulling the gearbox I wondering if running the engine without the prop would indicated rather the gearbox was the problem. I'd now it is very easy to overspend the engine w/o the prop on, just wondering if anyone had any experience with this.

Thanks

EG

[Av8r3400 1178]

I've done it. It is possible and won't hurt the engine as long as you watch the rpms. It will rev very quickly.

What do the plugs look like? Do they show a rich or lean indication?

How many hours does the engine have?

What prop are you running now and what has been run in the past?

Edited 2 Jul 2015 by Av8r3400

[egp8111 7]

about 450 hrs. Currently running an Ivo three blade. Had a three blade wood before. It feels like it's banging at idle. Smooths out above 3000 rpm and runs smoother but not perfect after I've flown it and it's been up to normL temps. Part of me wants to think carbs but I've had them apart so many times and they are in sync on the gauges. Prop tracks good and the blade pitch is equal. Gearbox ? errrrrrr

[wypaul 448]

Have you put new floats is the carbs in the last year and a half?  There was a bad batch of floats that made the engine run rich and out of balance but if you get them to sync at low rpm then that probably is not your problem.  I spent a couple of months chasing the same deal only to find out that the new floats were no good.  There is a SB on them.

Edited 3 Jul 2015 by Paul S