$150 is a pretty good deal running or not. even if you have to buy another motor somewhere you can get one for around 150 also. you're probably right, combination of old gas, maybe he messed up the carbs when he cleaned them or just didn't clean them thoroughly. he says it starts but only runs at 4-5k rpm. might be the idle screws are not adjusted properly or he didn't clean the pilot jets. starter motor is probably a broken wire or switch or bad contact somewhere. as far as compression, could be low. but 11,500 is not that many miles. mine has somewhere between 30-40k and I beat the snot out of it. they do kick pretty easily but I've never kicked a twin for comparison.