I have no spark on a sunl 250 4 wheeler i have replaced coil,voltage regulator,and cdi box?

If you have no signal from the crank, you will have no drive to the CDI and no spark.

noo 448results for yamaha 250 cdi box
its a voltage rectifier(regulator),
1971 Yamaha RD250 RD 250 71 Voltage Rectifier

There are three items that are connected together needed to create spark on your 1997 Honda 4-wheeler, regardless of which model it is.
Before we go through a checklist of these three important parts, look for a black wire with a white stripe that runs to the ignition switch and kill button from the CDI box. Disconnect this wire before it gets to the ignition switch and kill button, then check for spark. The most likely cause is a broken kill switch on the handlebar, or shorted ignition switch. Such a condition grounds this wire and kills the spark.
If this test did not restore the spark, continue reading...
Here is what is required to create a spark.

First, the alternator has one coil which generates a high voltage--about 125 Volts AC for the CDI ignitor box.

Second, there is a pulse voltage generated once every revolution of the engine that goes to the CDI box. This pulse causes the CDI to dump its stored energy from the 125 volt line into the primary of the ignition coil.

Third, If the two connections of the wire that runs from the CDI to the Coil are BOTH SHINY clean, the ignition coil will generate a spark.

If any one of these 3 don't happen, the spark will go away. Of these three, item 3 -- one or two tarnished and/or dirty connectors -- is the most likely cause. Just an added resistance of 0.3 Ohms or more in the CDI to Coil connections will cause the ignition to fail. No other wires have to be this clean.

possibly the rectifier faulty or stator coil

the things i would check are the pickup coil, the ignition coil, cdi box, the ignition switch and the kill switch. I just purchased a 4 wheeler that they changed everything electrical on it. come to find out the kill switch was melted onto the muffler causing it to be always activated. if you get a repair manual or look hard on the internet you can get the proper readings to ohm test your pickup coil, ignition coil and cdi box. the ignition switch can be tested with a test light and the kill switch should not be grounded unless activated. (hook a test light up to the positive side of the battery and then touch the kill switch wire. if it lights up there when not in the kill position you have a problem)

The Voltage From The Stator To The CDI Should Be Around 40 Volts(AC) At Cranking Speed. Be Sure Your Meter Is Set For (AC) Not (DC). The CDI Changes The (AC) Input Voltage To (DC) Output Voltage To The Primary Terminal At The Coil. An Electrical Shock Hazard Exist If Stator Voltage Is Checked With Engine Running. Always Perform This Test At Cranking Speed (R.P.M.) For SAFETY. 120 Volts (AC) Can Be Present With Engine Running.

Chances are it is a grounded kill switch on the handlebars or a side-stand / center-stand kill switch that has gone bad or is out of position.
Stick in a new spark plug also.

There are a # of things that can take your spark out, first I would see if you have power to your ignition coil (100V+). If none there you need to isolate your ignition switch (unplug it or take it out of the equation) and jump your starter solenoid manually or try pushstarting the bike. If still nothing check for voltage going into your CDI box, if none check for voltage out of your stator (over 100V) and your trigger or pulse coil (over 3V). If you find voltage at the stator and not the trigger replace the trigger and vice versa. If there is voltage for both replace CDI box (but be cautious to verify good ground for CDI box and ignition coil). If you find voltage out of your CDI box (over 100V) replace your ignition coil. Good luck!

see if you have ac voltage from the stator coil when cranking motor.if you do,try swiching cdi box out.also check for power to ign. coil.

The Sunl's are notorious for the stator going out. Check with your dealer for specs on testing the stator. It could also be the CDI unit too! I hope this helps