You said that you put stock jets in. Well from the factory shees are not jetted for everyones conditions. Say you live at 5000ft above sea level stock jets are not going to be the right ones. Also the temp could affect the jetting. I had a problem much like you discribe. I checked everything and it turned out that my pilot jet was way to lean ( I now use a 35) If your compresion is ok try bumping up the pilot jetts a notch or two and that should help with the hard starting.