If it idled that long it is either loading up and choking itself or it is too lean and slowly starving itself. If you idle for say 15 seconds and hit the throttle it will buck and stall if its loading up. If it tries to gain rpm but responds slow or stalls after it makes a try its too lean. You want to keep it a touch rich for a while even after break in let the metals temper and form their natural shape so you want that cylinder to be nice n cool and exchange that heat slower. This may require you to have a touch higher idle to keep enough air feeding into the motor. How close are your settings verse what the manufacturer recommends?
Thank you for the quick response! I think it is too lean based off what you said.
It says to turn the needle valve 3 to 3.5 turns before starting. And adjust it like 45 degrees to get the mixture right (if remembering correctly). After breaking it in I adjusted the needle valve to about 2 turns - I got best rpm this way, throttle control, and less smoke.
But it sounds I want it to be a little rich and less max rpm at first, correct? Also, how much smoke should it put out, especially when idling?
I am not really familiar with nitro four strokes as I am two strokes . I know they like a lot of oil when first breaking in so they can be a tad smokey. If this is a four stroke that has valves and a crank case with oil then no top end lube is needed so minimal smoke. If it is the type with the varied openings in the liner for intake and exhaust then you want a fair amount of smoke. Its best judged by temp range and how smooth the engine runs. I Always carried a digital thermometer with me when I ran my cars to help fine tune and ensure I was not over stressing things as I tend to be hard on things that move fast. Keep an eye on temps as per manufacturers specifications and all should be fine. Remember with these types of motors one setting does not cover all. You will have to tweek the tune nearly every run with temp changes and humidity and altitude as well for maximum performance and life span.