you could try a few things to trouble shoot this:change the needle and go up to a size 100 or even 1100 depending on what the fabric is ie melton wool, heavy coat fabric or curtain with suede backing. If it is denim then change to a denim needle which is blue coated as this helps the needle slide through this very densely woven textile. Always use a new needle for each new project as a needle will go blunt after about 5 hours of sewing or if it strikes anything. If you can hear a squeeking or popping sound, change it.Could you perhaps give some more details on the thread bunching and where it is breaking? is your top tension too tight perhaps. Also don't use that cheap thread that comes in packs of 4 reels in a plastic bag, stick with quality polyester threads like Molynecke, Guttermann or similar. The cheaper thread is not good for the tension device on your machine and will shed fibres, which can gunk up this device and affect the stitch quality.Unthread your machine fully and give the bobbin area a good clean out and oil any marked oiling spots with a drop of good quality clear machine oil. Check out my tip on winding a bobbin,
http://www.fixya.com/support/r10598580-winding_bobbin_correctlyit does make a difference in your stitching if the bobbin is wound unevenly or the thread is stretched, then relaxed as it goes onto the bobbin. If you visit this link
http://www.sewusa.com/Threading_Diagrams/Threading_Pages/Euro_Pro_Sewing_Machine_Threading/euro_pro_7500_threading_diagram.htm they have threading up diagrams for several model EuroPro machines; not yours but one of them could be very similar to yours and its free.Also on Sewusa, check out their "repairs" page and look at vertical hook bobbin tension images, it is important that that bobbin case tension is set correctly so check yours out vs these images; you need to be able to dangle the case by the thread tail and it should hold its own weight if there is enough tension on the spring, but still release thread when pulled gently. Also look at the top thread tension setting, should be on 4 or so, stitch length on 2.5 or 3 for heavy weight thread and you may need to loosen off the pressure on the presser foot if your model has this adjustment available. Hope that some of this maybe helps with your stitching problems.
