Bike pops and won't start.runs good a month ago but won't start now

SOURCE: yamaha 2003 wrf 250 start

hey m8,, sounds like u have a bit **** in the carb floating arround the jets m8,, wen its warm and bein used the dirt will flow round the carb untill left overnight to settle ,,that will block the fast idle jet,, need to take the bottom of the carb off,,ie the float bowl wip out the jet that the needle sits in to,, this will have about 4 little holes threw the stem of the jet, poke a pin or needle threw them and the main jet,, untill u see light threw the holes,, clean out the float bowl,, that should sort it,,

SOURCE: while riding my yz 125 it just died and won,t kick up again

• If a hole in the piston then install new piston and rings. Next, clean the carbon off the head and install a new head gasket.
• If cylinder wall is scared the piston has seized up. Pull the cylinder off and take it to the dealer. Have them bore the cylinder and return it along with a new oversize piston and rings.
• While at the parts counter, get a new stock spark plug and a supply of Yamalube Two Stroke Motor Oil. You need to add 4 ounces per gallon when filling up. This will be a 32/1 gas to oil ratio. NEVER ride the bike without at least the needed 32/1 mix.

SOURCE: no idle &bacfires on deceleration

hi mate on the carb you will find 2 screw 1 is for the idle and the over is for mixture the idle one will be the furthest out screw it in 1/4of a turns will the engine is running this will take the idle up on the engine and the backfiring is fuel in the exhaust not being burnt so on the over screw on the carb screw that in 1/4 of turns this will decrease the amount of fuel going into the engine if it still backfires screw it in 1/4 of turns again and see what difference it makes good luck

SOURCE: 2006 yamaha straoliner, engine code 37 comes up

Displayed Fault Codes For The ‘Liners

• 12 - Crankshaft Position Sensor <<Dead Engine>>
• 13 - Cyl #1 Intake Air Pressure sensor (open or shorted)
• 14 - Cyl #1 Intake Air Pressure Sensor (hose system) - Clogged or detached
• 15 - Throttle Position Sensor (open or shorted)
• 17 - EXUP Servo Motor Ckt. (open or shorted)
• 18 - EXUP Motor Locked Up – Frozen
• 19 - Blue/Black ECU wire broken or disconnected <<Dead Engine>>
• 22 - Air Temp Sensor (in headlight) (open or shorted)
• 24 - O2 Sensor – No Normal Signal Received
• 25 - Cyl #2 Intake Air Pressure Sensor (open or shorted)
• 26 - Cyl #2 Intake Air Pressure Sensor (hose system) - Clogged or detached
• 28 - Engine Temp. Sensor (open or shorted)
• 30 - Lean Angle Sensor Latched Up (Bike Laid Down) <<Dead Engine>>
• 33 - Cyl #1 L. or R. Faulty Ignition Coil << May Run >>
• 34 - Cyl #2 L. or R. Faulty Ignition Coil << May Run >>
• 35 - Cyl #1 L. or R. Faulty Ignition coil << May Run >>
• 36 - Cyl #2 L. or R. Faulty Ignition Coil << May Run >>
• 37 - ESC Valve Stuck Open (Engine Speed Control / High Idle Speed)
• 41 - Lean Angle Sensor (open or shorted) <<Dead Engine>>
• 42 - Speed Sensor – No Normal Signals Received OR Neutral Switch (open or shorted)
• 43 - Fuel System Voltage (ECU Unable to Monitor Batt. Voltage)
• 44 - Error In Writing Amount Of CO Adjustment To EEPROM
• 46 - Voltage To F.I. System Not Normal
• 50 - ECU Internal Failure – Memory Check <<Dead Engine>>
• 70 - Engine Idling Stop – After 20 Minutes Of Idling

gavin jones

• 1508 Answers
• Posted on May 24, 2010

SOURCE: I have a real hard time getting the bike started. ...

Many of those CRF have problems with the valves, check the valve clearances, as well as all the general maintenance items, clean carb, clean air filter, new plug.
If the clearances need more than one number smaller on the shims, it may be the start of valve regression.