Won't damn well run

[E74]

I had my CR125RZ stop on saturday at the lakes, did 4 laps and when I pulled into the pits it went pop pop, stop. couldnt get it started as it seemed not to have spark so I throw it on the trailer and dashed home to my workshop, found that it did have spark after all, it has a brand spanking new carbie which I cleaned right out, kick kick kick f*kin nothing, what I did find is that there was no fuel on the plug?, so I bunged a shit load of aerostart into the airbox kick kick kick f*kin nothing, still heaps of spark, swaped over stator/coil and CDI in case timing was the issue, still heaps of spark, kick kick kick f*kin nothing, then I pulled the carby back out and put my hand over the manifold, kick kick kick and the damned thing is blowing air back out of the manifold and not sucking, so no fuel-no run, anyone tell me what may be causing this?

[DR]

broken reed petals maybe??

[E74]

Nope, checked that.

[JohnnyO]

Broken woodruff key and the flywheel has spun putting the timing way out?

[E74]

nope, checked that.

[090]

Check air vent in the fuel cap.
Is the bowl full of fuel?
Um, sticking needle and seat
dodgey kill switch .
Spat a crank seal?
Have you thrown a bit of fuel down the plug hole?

[worms]

check that the main get is tight and not sitting in the carby bowl, fuel tap on tanks and as brad said the air bleeder on the cap,

oh well, it's a Honda

[Canam370]

Got compression? Might have run when the revs are up but once the rpm drops the losses are too great to run and you wont get it going again unless you tow it.

[huskibul]

 You didnt say whether you put new plug in it or not? sometimes they show a spark but just cant cut it under load,

[bazza]

spark    compression    fuel      but which one

[E74]

tried several plugs, now working on the compresion theory.

[Lozza]

Rear of the piston skirt cracked/broken off, trapped ring or holed piston? Would be the most obvious

[E74]

Big K was right, spose this'd do it..

[vmx42]

Big K was right, spose this'd do it..

What you left the piston on your desk!!! DoH!! 

[GMC]

Big K was right, spose this'd do it..

What you left the piston on your desk!!! DoH!! 

That reminds me of a tale my older brother once told me. (well, told more than twice actually )
One of his mates had a Austin Healy Sprite (many, many decades ago) and they rebuilt the engine with rings and bearings.
They were rushing to finish it to go for a trip up to the snow at Lake Mountain. When they got it running the oil warning light wouldn’t go out. They fiddled with it for a while and then decided the sensor in the engine must be faulty, it was sure to have good oil pressure as they had just put new bearings in.
They went on the snow trip ignoring the light, a good couple of hours each way. When they returned they drove back into the workshop and it was then they looked over to see the oil pump was still sitting on the work bench.

Couldn’t do that with a Jap car these days.