Hard Start of First Try

It has been one week and no reply from Lockwood.

I still am having rough starts. The OP described my situation exactly.  
This week, on my G3X, I downloaded the engine data. What I found was, on the first start of the day (the rough start), the Number One cylinder does not seem to get a good ignition while numbners 2, 3 and 4 all fire and come up to temp at the same time. Number one lags behind and after about ten seconds,  it lights off and comes up to match the others and the engine smooths out. If I shut down and start again, I get a perfectly smooth start with all cylinders firing off at the same time. 

I pulled the top plug and looked at it and it looked fine. I even gave it a cleaning. No change. My next move is to re-install brand new plugs into number 1 and see what I get. While I haven't looked at the bottom plug yet, it seems to me to resemble a fouled plug situation where the initial start burns off some debris. ??? 

Changing a procedure to smooth it out doesn't answer the question, "What has changed?".   

My issue was resolved merely by  changing start  procedure to run higher initial fuel pressure before start. I didn't look at engine data file. 

Was that higher fuel pressure achieved by using two pumps instead of one? 

Robert Carsey wrote:

If it's anything like the 912iS, there is a Start procedure in.the Rotax manual which calls for a specific throttle % when starting depending upon coolant temperature.  Some airplane manufacturers do not reference that chart at all which leads to rough starts.  As well, for the 912iS, you are to keep the starter engaged until seeing a specific RPM.  

Check the 915iS manual for a similar section.

You're right, I hadn't noticed before, but the 915iS OM says the following regarding starter engagement: 

"The connection must persist until the engine speed exceeds 1500 rpm."

I'll make sure I do that on my next start and see if that helps.

T Thompson wrote:

It has been one week and no reply from Lockwood.

I still am having rough starts. The OP described my situation exactly.  
This week, on my G3X, I downloaded the engine data. What I found was, on the first start of the day (the rough start), the Number One cylinder does not seem to get a good ignition while numbners 2, 3 and 4 all fire and come up to temp at the same time. Number one lags behind and after about ten seconds,  it lights off and comes up to match the others and the engine smooths out. If I shut down and start again, I get a perfectly smooth start with all cylinders firing off at the same time. 

I pulled the top plug and looked at it and it looked fine. I even gave it a cleaning. No change. My next move is to re-install brand new plugs into number 1 and see what I get. While I haven't looked at the bottom plug yet, it seems to me to resemble a fouled plug situation where the initial start burns off some debris. ??? 

Changing a procedure to smooth it out doesn't answer the question, "What has changed?".   

Not getting good ignition makes me think that possibly the A generator may not be producing enough power at that low of an RPM to sufficiently supply all spark plugs. My airplane POH says to turn on EMC/ECU backup (battery) power to power the lanes and fuel pumps, but then says to turn it off before the start.

I wonder if it might be better to leave it on until after start. That way the EMC/ECU is getting battery power throughout the start process. I know other airplanes have a "Start Power" momentary toggle switch that the pilot is supposed to hold until the engine is started. My plane doesn't have that, and I'm not sure why my plane's POH says to turn the EMC/ECU backup power off before start. 

If you look in the Rotax 915 OM, it doesn't say to turn off backup battery power until step 11, which is after engine start. Seems like maybe I should follow what Rotax says to do, rather than my airplane's POH in this case.