Hi Mozella,
Here's another link showing lots of smoke from a TriStar's RB211's engine.
https://www.youtube.com/watch?v=F8dezbfQC4I
"Because of a very weak APU, numerous engine starts were attempted and most resulted in "hung" starts, except for this one. After this engine (number 1) was started, they were then able to crossbleed to the other 2 engines which were then able to start normally. This start was almost a hung start as well, creating extra smoke, but then the engine does start to pick up RPM and is able to complete its start cycle. Any L10 lover will enjoy seeing this sight and hearing the sounds once again....Enjoy!!!"
If the APU was weak, the engine would not accelerate properly and to help it accelerate an "Enrich" setting was selectable. It was permissable to "blip" the Enrich on and off during engine start, between certain N3 RPMs. This introduced more fuel than normally scheduled and produced clouds of un- burned fuel. If Enrich was still on when N3 was above 35%, then to avoid starter motor damage, it had to remain on until start valve closed. If the APU was particularly weak, then this could mean a long time with Enrich on whilst the engine accelerated slowly. I suspect that is the reason for the smoke in the first video.
