well my 300ex is dead
I can't get the thing to run..
A few days ago my exectric start wouldn't work but i found the problem (loose flywheel) I tightend it up ... checked everything , spark, gas the works took the carb apart .. cleaned and adjusted it ... STILL won't fire ... I sat there for a few mins today and it just won't work .... It let out a huge backfire and that was it.

 

Well if your flywheel was loose U may have damaged your stator.

How good is the spark?Is it weak?

an engine needs 3 things to run.

Fuel
spark
compression


U just have to find which one or combonation of the 3.U said it back fired.Which may mean it is running rich.I have heard of a bike doing a similar thing to yours because they didn't have the carb slide in right and it was running WOT all the time.Have U changed the jets?IF so how big did U go.It would be your pilot jet not your main.



86 trx250r
97 300ex

 

Its got perfect spark .. it just won't fire... I know this because i got about 5 shocks trying to check the spark.

 

If the flywheel was loose then you prob spun the flywheel key and after tightening it down the timing is off. Take the flywheel off completly and replace the key with a new one then bolt it all back together. Bet it fires right up.