Every time I attempt to cold start my LA-135 it has to turn over with or without choke at least 30 seconds or so to start. After it has run even a few minutes it will start instantly after that, the rest of the day. Almost like the gas has drained from the carb. Is there a check valve in the line that may be stuck open so maybe it's feeding back to the tank???? There's no dripping or wet spots under the carb. I have tried starter fluid before turning over and with that it starts instantly. Gas is not getting to the cylinders on cold start. Any suggestions? I keep a trickle charger connected since the hard starting has run down the battery in the past. Also I change the plugs every year along with oil & filter changes every 25 hours. Any suggestions??