Carb sync?

JOEPILOT · #1 12-06-2015, 01:46 PM

I'm about to do the mechanical carb synchronization. In the Rotax maintenance manual step 6 says to adjust the idle mixture screws. To me it looks like the only way to accomplish this wold be to remove the carbs. Any thoughts?
Thanks, Joe

Rick_A · #2 12-06-2015, 01:58 PM

You should not need to adjust the Idle Mixture. You will probably have to adjust the Idle Stops - but just a little bit.

The mechanical sync on mine were pretty close right out of the box using Vans install instructions. It was only when I did the Pneumatic sync that I could see that an adjustment was required.

Bill_H · #3 12-06-2015, 06:55 PM

Remember, they rest run the engine pretty thoroughly at the factory.

Phantom30 · #4 12-06-2015, 07:32 PM

Quote:

Originally Posted by Rick_A

You should not need to adjust the Idle Mixture. You will probably have to adjust the Idle Stops - but just a little bit.

The mechanical sync on mine were pretty close right out of the box using Vans install instructions. It was only when I did the Pneumatic sync that I could see that an adjustment was required.

Mixture screws should be checked to ensure they are opened 1 1/2 turns...beyond that, they should be fine.

Dave12 · #5 12-07-2015, 04:54 AM

Joe, the engine in my first 12 ran flawlessly out of the box. It ran so well, I did not touch the carbs for 10 or 15 hours. My current mount ripped and snorted, had to be purged 3 times and took hours to calm it down. It now runs smoother than the first one, so be prepared for anything. The 912 is a great engine. I think you are going to like it.

Sink · #6 12-11-2015, 07:06 AM

Once the mixture screw is set on the bottom of the carb at 1.5 turns out it usually never changes. It is spring loaded with an "O" ring so it keeps its set.
Adjusting these screws as written in the manual also includes times when the carbs have been disassembled for maint. so if you are just checking a sync and this was done beforehand it isn't necessary to keep doing it.

Rotax engines can sound okay when running, but can be a ways off for a carb sync. The human ear can not tell the difference unless it is way off.
Always do your carb sync. Cables stretch, parts wear in, pulleys settle in, ect.... carbs can and will get out of sync as a new aircraft breaks in. If you do a full mechanical and pneumatic sync at 25 hrs. then you only need to do the pneumatic sync at the 100 hr. / Annual.
I'm sure Vans has already done a mechanical sync during their aircraft setup which can be checked instantly when you hook up a set of gauges.

I had one 30 year A&P said he didn't need gauges to set a carb sync and he could do it by ear. He was 6" of vacuum off. Use the gauges.

Dave12 · #7 12-11-2015, 03:03 PM

Quote:

Originally Posted by Sink

I had one 30 year A&P said he didn't need gauges to set a carb sync and he could do it by ear. He was 6" of vacuum off. Use the gauges.

Now that's funny! Reminds me of a mechanic I used to work with about 40 years ago that said he did not need to use a dwell meter to set breaker points, he set them by ear.

DaleB · #8 12-11-2015, 03:46 PM

Quote:

Originally Posted by Dave12

Now that's funny! Reminds me of a mechanic I used to work with about 40 years ago that said he did not need to use a dwell meter to set breaker points, he set them by ear.

Just his way of making sure he always had repeat business... From people with poor judgment. :-)