Dont use the stock DLE CM 6 plug , use a NGK CM 6 , If engine wont idle down instantly , the engine may be overheating due to a prop thats to small . . A glow engine will do the same thing if over heated. I have been using DLE engines for about 3 years , mostly in warbirds . I usually run them at wide open throttle , no problems at all .... and I also read an article recently about counterfeit DLE engines on the market ,the article depicted several ways to tell the difference . dont remember where I saw it , may have been on the DLE official webb site.