Cold weather rough start

Hi Robert

The injected engine starts on the B lane, it is richer than the A.  As soon as it stats you need to bring up the RPM to just over 2500 to excite h A Lane.  A has all the sensors and once it is excited A and B must synchronize.  In the cold this takes a bit longer, don't worry about sync errors, they are somewhat normal.  Try a few different throttle positions on starting.  If your G3X can display the TPS value set it to 60%.  This is important as there is no enrichment circuit, this ensures you have enough fuel and air.  Be sure you are ready to set the RPM as soon as it runs.  

Let us know if that helps.

Cheers

Start simple: Check the main battery voltage. I had similar issue with my 912iS two winters ago. The battery wasn't delivering enough power to the starter. It started but ran rough with heavy vibration until I advanced the throttle beyond ~60% to smooth it out, but the lane lights stayed on. Shutting down and restarting the engine didn't help. I did some research and learned that Rotax 912's have a minimum cranking RPM to start smoothly. I installed a new battery and the issue was resolved. Let us know if that works for you!

Reference: https://www.rotax-owner.com/en/912-914-technical-questions/2806-rotax-912-starting-rpm

I'm the other 912iS owner Rob mentioned in his post.  I have a video of one of the rough starts here:

https://www.youtube.com/watch?v=nGu0HDQ1Yhw

Hopefully you can see the engine instrument display in the video.  I will also note that if I preheat the engine (I have a Reiff preheater) over night, the engine fires up right away.  The video with the rough start was shot at 52F (according to the display).  I've had successful/clean starts down to 25F if I preheat over night.

I have the ECU logs if that would be helpful for diagnosing.

-bob

I agree with the above comments..

1) The IS engine, with a Glass cockpit needs a really good battery in the cold. Eventually I changed to a LFP (Earth X EXT-900) one which held over 13V during cold starts and spun the engine well. The Video sounds very sluggish.

2) the table in the IS Operators manual shows at least 55-60% Throttle for a good start at those temps.

Agree have hand on throttle and look for 2500-3000 rpm on start and then after a few seconds bring back to 2500 rpm.

Robert, and Robert,

What fuel are you using?  If you are using Avgas then starts can be tougher in the winter because of the fuels low vapor pressure (about 6 psi year round).  Winter blend auto gas has a much higher vapor pressure (about 13 psi) which is to ensure cars start easily in cold weather.  High vapor pressure fuel can lead to vapor lock in warm weather so it’s a double edged sword.  But if you are using avgas, mix in 1/2 auto fuel and see if that helps, or just try straight auto gas for cold weather.