Hi Folks,
I own an Eastwood 135 MIG welder and I have had penetration problems when welding anything over 1/8". I turn the heat up to max and turn up the wire speed to almost max and the wire actually hits the steel and pushes back on my gun violently. I have to turn down the wire speed until it stops fighting me and then I don't get penetration.
I will buy a better machine as soon as the budget allows, but when you're not a pro and you have a cheap machine, you're always wondering if it's me or just a crappy machine.
When I weld 1/8" or smaller, i can lay down some awesome welds that penetrate nicely, so i believe it's the machine.
Your welder is rated for 3/16 on mig and 1/4in with gasless flux core. Go back to your settings that worked for 1/8 material and increase slightly for thicker material until the weld is ok again. There should be a chart on the welder to give aprox settings for different metal thickness. For thicker metal and more penetration you could consider switching to flux core wire which is more tolerant of not so clean material and conditions such as breeze. I have seen good things on the forum about Eastwood so it's probably a matter of practice to get where you want to be. Search " flux core welding" and see if that may be an option to get more bang for the buck. 
1/8th is really the practical limit for a 120V MIG welder. If you need to do more, either invest in a bigger MIG or learn how to stick weld and pick up a cheap/used stick welder on Craigs List. Something that does AC and DC and goes up to 200 amps, like a miller thunderbolt.
Multimatic 255