added to the above, bad fuel, weak glow plug can also cause this. Also it can be too rich...if its too rich the crank case will load up with fuel, and as soon as you go to WOT, it will throw a bunch of fuel into the cylinder, causing the plug to cool too much or just load the piston. You may also find other answers [link=http://cajungatorairboats.com/v-web/bulletin/bb/viewforum.php?f=9&sid=4d92fb3c8c0a23e38fa505f28976 da97]here[/link]