The most important thing for me to know is what was done between the last time it ran and the time you tried to start it but it wouldn't catch? If nothing, say so.

Motors are fairly simple contraptions. And the bike electrical isn't terribly complicated. So, it's not going to be a 1 in a million problem. To get it to run you need fuel, spark, compression, and air. You say you have all of them. You must be wrong.
Does it catch a little bit ever?
Does it backfire ever while cranking it?

Try this: turn the fuel to OFF. Crank it for a few seconds (like 5). Wait a few minutes. Turn the fuel ON or RES. Roll the throttle between 1/4 to 1/2 open while cranking the starter. You might need to crank it for a bit (7 seconds max.) If it doesn't fire at all, give it a minute and try cranking it one more time. Don't go too crazy on the starter. It is possible to burn it out from too much cranking. Let me know if that worked, or caught at all.
By the way, make sure your battery is FULLY charged!

 

headlight comes on, it already says i've got good readings from electrical, and that we have good gas flow,

stage 2 jet kit and tuned for yoshi, new fuel pump, new rings...great compression, plugs, wires, rec all replaced this year, battery charged and i have cables run to a brand new car battery for extra gusto....basically it wont stay running, you can hear that its running when the starter is going(and feel hot exhaust...so ive got combustion....but it wont sustain....) but it dies out after you let off...

ive rebuilt bike motors from triumph to honda cb's and i REEEEALLY am stumped...

my buddies shop, hes been a harley mechanic for 30? +- years and is VERY reputable around town, i met him while i was ads mgr for thunder roads mag. this place is not some hole in the wall fly by night crap....probably 10k sq ft and slammed with bikes 24/7 so i can't get it in for free work....

i used to be a control systems design eng. for a rig support/compressor supply company....so i know things SHOULD be working....

seriously? im stumped.....and o yeah, heres a pic of my thumb....IVE DEFINATLY GOT SPARK! lol



[IMG]local://upfiles/20875/168071D23FCC4186923114858346235D.jpg[/IMG]

 

one more thing-so i dont sound like an ***-

i really do appreciate the time you ahve taken to reply to my post!

any little bit may help!

 

So, when you shocked yourself...did your arm go flailing all over the place?

Ok...let's see.

Components of ignition [ul][*]Battery[*]Main Fuse[*]Ignition Switch[*]2 more fuses[*]Sidestand indicator light[*]Sidestand switch[*]Engine Stop Switch[*]Ignition Control Module[*]Neutral switch[*]Ignition Pulse generator[*]Ignition Coils[*]Spark plugs[*]Spark plug wires[*]All other wiring between components.[/ul]We know a spark is getting there...is it getting their at the right time? Try unplugging the ignition control module (ICM behind the R/R) and plugging it back it, maybe check all the connections in the harness (page 16-6 in the service manual for what should be tested for each lead. Maybe something is screwed up in one of the wires.

Is everything properly grounded? Reseat the Spark plug wires back onto the spark plugs (take off and put back on). Is it possible that 2 of the wires are on the wrong plugs? You have the spark is it a weak spark? You don't have a CA model bike, right? if so, could be a faulty EVAP purge control valve. Are the cylinders flooded? air cleaner dirty? Good Fuel-air mixture?

 

hmmm me thinks the vacum line is the only thing it could be? dude, im stumped..this thing is going to the shop....

 

Well, you said anytime you take off lines, you have fuel. That means your vacuum line is working, unless there is something wrong with the petcock.

Ok...so you try starting it...how long do you try? On and off for 10 minutes? If you open the gas tank after that, do you hear air rushing in?

 

I had the EXACT same problem, and I cant tell you what fixed it... Why? Because I dont know.

I too was stumped, and very frustrated because you and I probably have the same mechanical aptitude. I rebuilt the carbs, POR15'd the gas tank, replaced fuel and vacuum lines, rebuilt the petcock, replaced spark plugs, checked EVERYTHING and could not get the stupid thing to run unless it sat for a LONG time...

When stone cold it would start up fine with the choke on, but would bog down when it warmed up or if I even touched the throttle.

For some reason it works fine now, but I used to be able to fill my gas tank up to the brim, now if I do this and ride for a bit then park the bike it spits fuel out of the overflow tube.

Wish I could help dude, but my bike just for no reason started to work so I have left it alone...

 

Sounds like your electrical is fine. You are getting gas/combustion. You are definitely getting spark.
You are getting compression.

That leaves 2 things. Timing, Fuel Quality

When you replaced the rings, did you mess with the timing chain at all?

Replace the fuel. Fuel definitely goes bad. I've had engines sound just like you describe yours, seemed to run while the starter was depressed, but would not sustain whatsoever. Everything seemed ok, so after scratching my head for a while I replaced the fuel....it fired right up.

 

If everything you've posted really is true, it can ONLY be 2 things: bad gas or dirty carbs.
When was the last time the bike ran? Was it like you rode it yesterday and everything was fine, and then today it won't start?
Have you tried bump starting it? Do you smell gas when you take a whiff from the tail pipe after trying to start it?
I would go to the gas station, get a gallon of gas in a plastic gas can and try the new gas. Take your tank off, plug the vacuum line, and pour your fresh gas directly into the fuel line.

 

Spurious original post!