Got it from a neighbor and cleaned the carb and gas tank and it fired right up, it ran great for about one month, but then at half throttle it started backfiring. I took the carb apart and cleaned it again, set the mixture screw and checked the voltage regulator. Ended up replacing the carb, but then at half throttle it would start bogging down. I could put a rag over the intake and it would run perfectly fine, so it's not getting enough gas, right? So I went through the new carb and set the clip on the needle that goes down through the diaphragm, to the third place from the top. Nothing! The carb is getting plenty of gas it is just not sucking it up. The jets are clean, I think, because its a new carb, right? The spark plug coil is fine, so is the spark plug. Could it be something with the valves? I don't think that the timing is off because it wouldn't run with the rag over the intake. I don't think that there is a compression release on the quad master 500. Don't know if this helps but after running it for a little while backfires out of the muffler. Any suggestions?