Is it a VX engine? I have a 180vx and a 220ex. On the 180vx, I had lots of trouble during starts. It was primarily due to me using a 3S Lipo. At the time of the 180vx, the factory supplied pack was a throw away item - no good at all. I 'upgraded' to a 3S Lipo - didn't help.
But when I put in a 4S LiFE, all my problems went away.
These engines need a LiFE 4 cell pack to have reliable starting.
All new engines from Evojet are now LiFE pack supplied.
If you're looking to buy a pack, just get a 4s LiFE pack and be done with it. Don't bother with a 3S Lipo.
Hope this helps.