I have a 25 kawi twin vertical. It has about 2000 hours, but has been maintained. It starts and runs great. When I go to shut it down I bring the throttle down then shut the key off as always. Lately though about 3 seconds after shutting off it will pop once. If I let it idle for 2-3 minutes it won't. This has been for about the last week. I checked replaced the filter and prefilter, when the filter was off I tried it a couple times and could not get it to pop, but a new filter did not make a difference after a longer run. Choke is open, and as far as I can tell the throttle is all the way down, though tomorrow I am going to check the idle speed then run it and take the cable off and then shut it down to see what happens. Any ideas?