This could be caused by a lot of different issues.
1. Are your seps good? Have you looked at them on a light table to make sure they register?
2. Are your screens tight? Make sure your screens are over 20 newtons. preferably 25.
3. Are you flashing the yellow before you hit the red? I assume you are but, I'm just listing possible issues.
4. Do you have enough stencil on your screens? An extra coat or two of emulsion will help the red sit on top of the yellow.
5. Excessive print pressure will cause the ink to flatten and spread beyond regular dot gain.
6. Off-contact. If you don't have enough off-contact, your screen will sit on your design and smear.
7. Is there any play in the heads of your machine? You'll never get consistently good prints if your press is sloppy.
The ideal way to print this job would be to use a white base and sep the red and yellow so the yellow is not the base, Base screen 130 to 156. Print the base, and flash. Print the red on a 170, then print the yellow last on a 170. Try to do the red and yellow with one stroke. You don't want to put a lot of ink down. Too much ink causes orange peel and can cause bleeding. Medium squeegee durometer and fairly sharp edge. Lastly, yellows can be a little tricky because they are pretty transparent by nature. If you can cheat a little toward gold it gets a little easier.
Good Luck.