Did you burn up your brakes? Sometimes if the brakes are applied continuously while the quad is driven a long ways the brak pads get glazed and don't grab anymore. You'd know this if it were true. Youd be wondering for miles why the quad doesn't have power, then when you finally stop the smoke rolling off the brakes could not be ignored.

I'm actually much beter at electronics rather than the mechanical stuff. Don't get me wrong... I'm mechanically inclined. I have a machine shop in my garage. I just don't have as much experience as some others when it comes to quad engines. My quad doen't break that much.

10W-40 is what I use. That doesn't seem too thick to me. These air cooled engines can get hot, and thicker oil won't get too thin at high temps.

Are your back brakes hydraulic (like my quad) or a mechanical cable link? If hydraulic then they should be self adjusting unless air is in the system. In that case the brakes will have to be bled. If it is a mechanical cable link then I have never seen one of these, but I would guess there is a mechanical adjustment at the lever that lengthens the effective cable housing. Usually you loosen a lock nut, then rotate a hollow screw like fitting till the brakes grab tight when applied.