honda rancher 420

doesnt cold start very well, any ideas?  

change the spark plug and clean out the carb.
change the air filter if you haven't
 also check the stator and magneto for rust or dirt at the pick up points, clean it if necessary.

though normally on honda it's the carb nastied up.
a good cleaning in most cases will make them work right.  
Keep it RUBBER SIDE DOWN!!

i forgot to mention its efi? i did wash air filter and changed plug, nof dif  

I am still not used to the fuel injection being on atv's myself.
I actually prefer the carbureted versions, easier and inexpensive to repair. and you have a choke.

fuel injection is cool until you go to repair it or replace the injectors.  some injectors can cost as much as $300.00 each.

check the stator and magneto for rust, dirt. etc.
also check to be sure the stator is putting out the proper amount of voltage, check the coil for weak spark.

also have the valves checked to see if they are still in "lap"  

make sure you are burning 92 octane or higher fuel, lesser octane fuels will excessively carbon up the valves causing a loss in power and hard starts.  
Keep it RUBBER SIDE DOWN!!

thanks for the advice  

Make sure you keep your thumb OFF the throttle while you're starting it.  

cylinder head sensor was bad  

That'll do it. Glad you got it fixed.