125 Staled At Track And Wont Start It Backfires.

[caleb99]

Hello, i bought a bike 2003 kx125 and did a whole new rebuild on the top end and went throught the whole thing and the thing ran like a champ i was at the motocross track one day (3 months after rebuild) and it had been probably an hour and a half rideing so i took a break and then started up my bike to go ride. on the third lap on the track i came up to this corner really fast trying to pass a guy so at the last secound pulled in my clutch and slammed on my breaks. my bike ended up dieing and so i pushed it off the track to try and start it, after 30 or 40 kicks it wouldnt start so i took it back to the pits to try and push start it with some help and it does nothing but bog and back fire…so i took it home got a new sparkplug, cleaned the carberator,cheack the flywheel key and it was not sheared or spunned it has good compression at least what i can feel from kicking it and im completly stumped at what is wrong im going to look at the reed tomarrow becouse i forgot to when i took the carb off but again it has good compression but ill cheac that just to make sure. so any suggestions on what to do would be great!

 

[truespode]

Sounds like you looked at a lot of things and know your way around the engine so I am hesitant to ask but did you check for a spark? It may be weak.

Could anything be blocking the air flow?

Ivan

 

[High Lord Gomer]

Like you, my first thought is the flywheel key sheared and second to check would be reeds but they don't usually have catastrophic failures.

 

[truespode]

Like you, my first thought is the flywheel key sheared and second to check would be reeds but they don't usually have catastrophic failures.

Reeds are a good thing to look at.

I forgot all about it until you mentioned but in 2001 at the TNT Spodefest I had a set of Vforce Reeds on my YZ250 and the reeds blew to pieces and it had a very similar effect. It wouldn't start and it backfired a little bit when kicking but seemed to just flood the engine.

I put the stock reeds back in and rode the rest of the weekend and fully believe that is why I didn't win that wheelie contest :)

Reeds is definitely worth a check.

Ivan

 

[High Lord Gomer]

You blaming this on reeds?!?

 

[truespode]

That is my story and I am sticking to it :)

 

[caleb99]

yes very strong spark the redd is the only answer so ill have to cheack that

 

[caleb99]

the airflow jet in the carb got a little cloged but when we blew in it some crap blew straight out but when we put it all together it was some problem

 

[truespode]

Did you by chance do anything to the choke that could have it stuck?

 

[caleb99]

no the chock works just fine but it doesnt seem to make a diffrence with it on our off.

 

[truespode]

Have you pulled the head and looked for anything on the piston or if you have a broken ring? Possible air leak?

I am scratching my head... I am not much of a mechanic at all but would think with what you have done something regarding electrical, fuel or air should be presenting itself by now.

Hopefully one of the guru's in this forum can chime in with more questions that may lead you down the right path to a diagnosis.

Ivan