Misfire problem on 50tlr 2 strk

[Eastexn1]

Have a 50 HP, 50TLR, 2 stroke. Purchased with no history. Engine had been left to sit for a long while. I dumped 15 gal of gasoline and replaced with new fuel, drained the fuel bowls, replaced the fuel hose. Engine ran rough, hitting and missing. I cleaned and installed new kits in all 3 carbs, installed new fuel pump, rebuilt the primer assembly, installed new spark plugs, and installed new prime starter as the original was defective. Reset the pilot screws to 1 1/2 turns out.

Engine will start immediately but will misfire, probably on the #1(top) cylinder ever 4-5 cycles. Misfire seems to be on the compression stroke. When the misfire happens it almost kills the engine as it is firing against the normal turn of the engine. #2&3 plugs look good, light tan and dry. Top plug is black/tan and damp. I suspect the ignition is coming from the CDI but it is too early.

I am at a total loss. Any ideas really appreciated.
Thanks in advance.

[99yam40]

this the same motor that would not start cold before?

sounds like a lean sneeze .
make sure you follow the link and sync procedure any time you put the carbs back on.

make sure the carbs are cleaned properly

[boscoe99]

My data for your model shows 1 & 5/8ths turns outward for the idle mixture screws. Plus or minus 1/4 turn.

The motor was made to run lean. Very lean. So damn lean it can be a problem. If you are using gasoline with ethanol it will only be worse.

Were the carburetors completely taken apart and cleaned in a heated ultrasonic cleaner? Were all of the passages rodded out and verified to be clean and open?

The 50TLR is right behind the number one leanest running Yamaha made. Number one being the dreaded F40 with carburetors.