912ULS cold start impossible

Have you definitely got spark and is fuel getting to the cylinders? I know that the Ignitech units have a 12V supply to aid starting, is that definitely wired correctly and working? Could the trigger coil gaps be on the limit?

Hi Tjeerd

First, try to start using a battery booster to be sure that the crank is turning fast enough.  You must have at least 225 to 250 crank speed to get spark.  if you have a low battery and are only getting a 90% of that speed you will have no spark.  As we know the temperature can be an issue. 

Also check your positive wires to the starter from the battery and be sure that the connections are tight and no loose parts.  

Check to be sure you also have some fresh fuel, old fuel may not flash correctly in the cold. If you are using Avgas then you may need to warm the engine (hanger or warming devices on the oil and especially the cylinder heads) Avgas has low vapor pressure and is always hard to start in cold weather. 

Cheers

Thanks guys,

Starting with a booster improved starting but is seems still difficult to get the engine through compression. It is still cold here, that doesn’t help.

We loose some 1,5Volt during starting from the battery in the back of the plane to the starter motor, that is to much. So we started building the battery back to the original position at the engine side of the bulkhead.

Today we found out we have a black starter motor, normally used on a 80HP engine; we have 100HP. Another Rotax owner pointed out we should be looking at a silver/gold coloured one as he has, on his indeed quicker rotating engine.

Is this correct, has the silver/gold one more torque and/or power to get a better starting behaviour?

Nice to hear from you!

You’ll be better served using the stronger starter for your engine, that’s for sure.

Besides, the ignitech modules produce a spark on the separate 12V (superb feature) wire or without it but they do not really require the minimum rev as the rotax modules do. A good battery status and wiring play a role, particularly during cold times, but you should try the larger starter for 100 horses.

Tjeerd wrote:

Thanks guys,

Starting with a booster improved starting but is seems still difficult to get the engine through compression. It is still cold here, that doesn’t help.

We loose some 1,5Volt during starting from the battery in the back of the plane to the starter motor, that is to much. So we started building the battery back to the original position at the engine side of the bulkhead.

Today we found out we have a black starter motor, normally used on a 80HP engine; we have 100HP. Another Rotax owner pointed out we should be looking at a silver/gold coloured one as he has, on his indeed quicker rotating engine.

Is this correct, has the silver/gold one more torque and/or power to get a better starting behaviour?

Nice to hear from you!

I had this same issue many years ago. The old black colored starter, too small a battery that was too far away that needed larger wiring. So I replaced the starter, installed a more powerful battery and larger wire. Problem solved. It would fire right up every time after that.