Premiere Rush File Size Larger Than Combined Clips

[TheMcQueen]

I have one video, in 720p, of the MP4 file format. It's 4.6 MB.
I have a second similar video, also in 720, MP4 - but this one is 11.9 MB.

In Premier Rush, I simply combined them together. I separated the Audio Track from them both, and deleted them. I then added a single, Wipe Left transition between the two clips. 

The exported file size to MP4, is now 143 MB. 

What has caused this to happen?

Additional info: 
I tried again just adding the two clips, and it also returns a similar file size. This is without the removed audio files, and transition.

[cheryld86444304]

I have a similar problem - I'm importing a 2-hour video, cutting it down to 1 hour, and the result is a file 6x larger than the original. I finally got that to render, but I cannot get it to upload to youtube. It's not the first time I've edited a video to be shorter and ended up with a larger file. I don't understand that.

[MrTrainee]

same problem, a 1.33GB mp4 file with a few pieces cut out became a 13GB file...

[cheryld86444304]

I ended up using theWindows 10 Photos app. It took me less than half the time to cut the parts I didn't want and I had no issue exporting and then uploading to youtube. And, the final file size was just under the original. I'm done with Rush.