hi hi have a s254rmck that wont run right after it has been running for about 5mins it dies off and wont respond to the throttel have tryed a new carb still the same wondering if it could be electrial when motor warms up any help would be good

Try closing down S/P gap to @ .015"
Next remove black secondary coil and lightly sand the surface of the brass grounding tab on the one lug, place a daub of dielectric grease on that spot and screw coil back down.

Have you had to relocate the coil? If so, check your ground; run it to someplace on the case. I tried running mine to the starter cap screws and had the same problem. I created a new ground wire, put a new bolt on the case to run it to, and the problem went away. Bruce at Gizmo diagnosed that one. Also, if you're running standard Zen mounts, you need to either shim the starter or mounts. Easier way to tell is to look at the bolts on the case, if any threads show on the back case where the mounts are, or are flush add a shim to the mount, or add them to the starter. Mine are on the starter (I have Top Secret mounts just as a reference). Thanks to Scott for that piece of advice. The starter doesnt move out of the way, and the starter dog WILL eat the starter or do damage to the motor. Other than these pieces of advice the RCMKs run great!

My RCMK ran great for the first 2 tanks and then the problems, just as you describe. Changed out a heap of things no difference. Changed the secondary coil to a Zenoah and ran the ground to the motor and like magic no more issues. try it first and save your self some grief.
Cheers Andym

I have over two gallons of fuel through my RCMK with no problems at all. I did run a extra ground wire from coil ground to case. I used small stainless star washers to make sure its make good contact. I also run my plug @.014.

i have the same problems i think? RCMK run about 2 24oz tanks through it at 25:1 oil ratio then first tank at 40:1 it started fouling plugs and idle drops off? then it became a case of idle ok but blip the throttle it would rev up sluggish then die? you could start it again but blip the throttle again it die?(blowing fuel mist out the carb?) hold it down and it will rev then just starts to choke and then die? ive changed carbs changed pipes plugs wired it up again changed fuels and it still does it? after reading this i may re look at the coil? as every thing ive seen points to fuel but its had me stumped for a week now!!