lacks power/cuts out when engine is warmed up

[beaterelite]

i have an 01 sa50p. high miles-7000 when engine warms up it starts cutting out at half throttle or more. i can feather throttle to maintain engine speed but full throttle will stall it. here's what I have done so far..


disassembled carb and thoroghly cleaned twice, replaced intake and reed gaskets, removed head and cylinder for decarbonizing-lots of carbon in exhaust port hardly anything in combustion chamber, replaced rings and gaskets, filled and flushed muffler w/ovencleaner then bbq on grill for at least an hour, new plug installed.

this improved condition but still cuts out when temp goes up. on first run got sparks out of muffler and now has minor "backfire" noises but runs perfect at less then half throttle good to about 15-20mph not near the 30-35 it used to do


need your help to save this little beater!! wife says figure it out or ditch it. taking too much time to get right.

[tucker]

couple of things I would look for that are cheap. Check the air filter, looks like you cleaned/changed most everything else. I am not familiar with this model but it is an internal combustion engine and with those I am familiar. It will need a rich mixture when cold and starting. Does it run wide open, max rpm, when cold if you give it throttle? And is it capable of doing that til the engine warms up? If so, then I would suspect that at operating temp the mixture is too rich because the air flow is restricted. Check the plug after running it for about ten minutes before you clean the air filter. Is it tan or is it black. Tan is good. Tan to whiteish tan is getting bad and it is running too lean which might be caused by an air leak which would happen when the eginge gets up to operating temp and parts expand in areas where you do not want air being ingested. If the plug is black then the ratio of fuel to air is too great for that rpm and operating temp. If the operating temp is going up and the fuel supply remains constant but the air supply is restricted by a dirty filter then you will end up with a richer mixture and thus the restricted rpm. Or it could be that the carb is not as clean as you imagine, they never are, and you still have a restricted fuel flow. Has the gas tank been cleaned, you mentioned it was high mileage and that means tank trash. Does it have a fuel filter and has it been changed. How is the compression? Some of the specifications for engine rebuild are very important, some are less so, but the overall average needs to be on the higher side. Sticking new rings and gaskets into and on a cylinder that is out of tolerance will get you the equivelant of a loose fart for power. Did you check the resistence on the plug wire? It may be too high as it get warm from the engine heat.
Check the primary and cheap stuff first. Fuel, fire, compression, and air supply.
And beware of free advice!!!