I have a honda 5.5 HP engine on my pushmower, it runs about 3 mins. then starts missing out, backfires through the carberator, then dies. I have checked: the gas cap for vaccume, fresh gas, new plug, cleaned carb, I hooked up a spark tester to it, and started the mower, and watched the light on the tester, it never went off at all, even when it started missing out, it was still on, then it backfired through the carb, and died. Could it be a valve sticking, after it warms up, making it backfire through the carb?? because it still has spark after it dies, but it wont start back until it cools off a few minutes later. If it's not a sticking valve, then I'm about out of ideas, any help would be appreciated!!!!!