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Hello to anyone who reads this. I am Jon and I own J&M Outdoor Power, a very small, small engine repair shop. I was approached by Coleman about 6 months ago to become one of their Warranty Centers. I recently received 3 different UT400's and a UT500 all with similar issues. These units range from 2 months to 2 years old. Customers state that the unit(s) was/were running fine, then heard a pop and a loss of power, two would no longer start. The two that would run would not achieve normal operating speed (around 20mph I would say) without redlining the RPMs. I quickly found that the Valve lash on each unit had become too large on some(both intake and exhaust) and too tight on one(just intake). After setting the gaps to .005(I found multiple different people suggesting bigger and smaller gaps, but no definitive Coleman Spec number yet) every unit starts, runs, and achieves top speed without issue. I don't know how many others have come across these issues, and I wanted to get something out on the web for others in the same predicament. Please let me know if you have had similar issues. Edit: I realize that this will not be a fix all solution for this issue, as the oil level and condition should be verified before moving to the valves. Many times improper oil conditions will cause valve lash to change. These units all have good oil and proper oil changes.