I'm looking for some help, because we have run out of ideas. My brother has this 05 YFZ450. Sent the engine of to have race mods. They sent the engine back. Put everything back together and it won't start. We have went through the entire thing using the wiring diagram specs from the dealer. ALL ground wires have continuity. We have replaced the stator, pickup, cdi, spark plug and the battery. The coil tested out good, and all the wires are hooked up according to the diagram. The thing cranks and cranks but wont fire. Does anyone have any other suggestions of things we could try, because we are out of ideas. Any info on this matter would help. Thanks!

 

spark plug? valves? timing? sounds like a dumb one, but is there any gas in the float bowl?

 

crank the motor a couple times and check the plug to see if gas is flowin first.

 

Changed the plug, yes there is gas in the bowl, but the timing is something we need to look at. Thanks. You know you go over these things in your head a hundred times but there always seems to be something you miss. That's why I come to this forum!! Thanks again and if anyone else has any suggestions please feel free to reply.

 

what about checking the fuel/air screw. the pilot screw? or maybe checking the fuel line/filter for a clogg.

 

Have you checked for spark? And do you have spark?

 

NO SPARK!

 

well, that would be the problem then.

 

Boy, you got some work ahead of you. Its a different situation when the motor comes completely out and is reinstalled. There are so many things which can be wrong.
Id start by assuming the motor work was done correctly, and that theres something not hooked up right or unconnected.
So, the motor will turn over with the starter...but no spark? And youre checking for spark , by holding the spark plug against the head, and watching for spark? This eliminates a timing issue for now. We just need to know if theres spark anytime. Gap is correct?
Look over all the connections, fuses, battery charge. Kill switch , throttle switch,carb switch, main switch, clutch switch, neutral switch.
Do you have a wiring diagram? If you dont, pm me with your email address, and i can send a jpg of one.
If all the switches are hooked up and correctly, then Id start ohming the coil, and pick up coil.

 

Found the problem, it was the TP (Throttle Position) sensor or switch was stuck open. Anyway we've fixed that and it's running great now. We'll be racin' in the am. Thanks for all of your suggestions it really helped us go over it with a fine tooth comb without going out of our minds!!! We really appreciate the help!