I'm having a similar issue with my Coleman UT400, but it started after we left it out in the rain over night (we usually keep it in the garage). We were expecting a large delivery, so needed the garage space for a couple days, and got an unexpected rain shower. When I went to bring it back inside, it turned over fine, but would not fire. I ordered/replaced the CDI, voltage regulator, and coil and still would not start. Cleaned the plug, and it fired right up ... this time. After a few short runs, it quit starting again. The plug was wet fouled with fuel. The same NGK DR8EA as mentioned above. I picked up a couple new ones, but now I have to rotate those in about every 3 starts ... either it won't start, or shortly after starting, it will stall and not refire. Also, when a new/clean plug (I clean them with alcohol and then sandblast them real quick) is put in, it will crank in a couple of seconds, but subsequent attempts will take running the starter motor for 10-15 seconds before it fires. Googling brought me to a page that said Hisuns were bad about bad/dirty injectors causing fouling (I have always run premium with stabilizer in it), so I ordered and replaced the injector too but experienced the exact same issue. Seems like the next thing to try would be the ECU, but that's a little pricey, so I'm hoping for other suggestions before I go there. Now, I did try a hotter plug (DR7EA) and it seems to not foul as quickly, but from the get-go it has taken a lot of cranking on the starter to get it to start up, but seems to run better once started.
