ytm200 runs better when cool outside?

[kawaboy-zx12r]

I have a strange issue with my ytm200. i have noticed over the years that it only runs good and strong when the temp outside is 65 degrees or less. can anyone think of what the issue could be? i put all new stock size jets in the carb, changed ignition coil, spark plugs, checked for bad wires and nothing i tried makes it run better when above 65 degrees. its a bummer because i cant enjoy it much in the summer, but in spring, fall, winter and cooler nights it runs REAL strong. when i bought it the stock air filter was trashed so i got an aftermarket air filter made by moose, it appears to be the same foam as the stock air filter was. but its yellow instead of grey/black. any suggestions appreciated. Thanks

[muthey]

sounds like temps above 65 it is running rich so you can do plug chops to get it to the right jetting, or maybe there is an issue with electrical that when it is hot it is shorting in the cdi or stator. start with jetting first, reason being cooler temps cause a more lean condition on motors.

[kawaboy-zx12r]

thank you for the reply. the stock size main jet is 112.5 so i should buy a 110 main jet and leave the needle in the stock position (middle clip slot)? Thanks

[kawaboy-zx12r]

let me know if i am on the right track here by ordering a 110 main jet, maybe the moose air filter is more restrictive than the stock filter, i also used K&N oil filter oil on it like i do all my foam filters.

[muthey]

you can try a 110, but also check to see if there is a blockage in the breathing part of the frame with the airbox, any thing that might restrict airflow. Is it oem carb or china aftermarket? also where did you get the new jets from some of the chinese ones are not the right sizes that they are stamped.

[Racer-X]

I don't think the air filter is causing any problem. Have you tried adjusting the air/fuel screw on the carb at all? Also when you switched to the new jet size was there any difference at all?

[kawaboy-zx12r]

i checked for air blockage several times over the years. its the oem mikuni carb, i bought the stock size jets from the local yamaha shop, but i dont know if they are genuine mikuni, it runs the same as it did before i put new jets in (same size). i have tried adjusting the air/fuel screw 100's of times. i havent bought a new 110 jet yet, i was just making sure 110 would be the one to get. thats the next size down mikuni has listed from the stock 112.5