glow plugs will eventually burn out and need replacing. if you have trouble starting the motor then always check the glow plug before messing with the needle settings.
if she is spitting fuel out the exhaust then you can surely lean her out.
the trick to tuning any nitro motor is to turn the needles in VERY small amounts. starting with the high-speed 1st. tune that needles untill she sounds good at WOT. you shouldnt see fuel/oil spitting out the muffler, but there should be a stream of visable smoke. if there is no smoke, then it is too lean and you need to add fuel.
after that is set good, tune the low-speed needle so that the buggy accelerates good-without any sputtering or bogging.(bogging means too rich, and sputtering means to lean.)