..scoot shuts down..

[wordslinger]

...reeds are not cracked...

..plug is medium brown, clean and dry...

[art]

That was my next guess piece of reed plocking port,vaper lock maybe,unscrew gas cap  You made me a hero Ha!Yes hair is falling out and going grey.

[wordslinger]

..now, this is the first time i've ever looked at a reed valve assembly.....


...there is like a black, coating of some sort, that LOOKS like it has been deteriorating from the reed valve assembly...

..the reeds themselves are intact with no cracks or missing sections...i dis-assembled the whole reed valve assembly to check them out..

..and they are made of a fiber material, not stainless steel...and they too, are dry...but i got boo-coo fuel at my carb's intake side...

..even sprayed starting fluid into the carb as i was cranking the starter...

..no fire...

good spark, but no fire...

[art]

You did put fuel in the sparkplug hole and try to fire? The start circuit does bypass the rest of the carb through the choke porting

[wordslinger]

..no, didn't do that...

..shouldn't my plug and combstn chmbr be flooded if fuel was getting from the carb, by the reeds??...


..aannnd what makes the fuel take that path....

[art]

Ya had a good look at mine today same thing,would have to have a large piece of reed to block a port and fiber should get eaten up and spit out if running when it happened,I'd say clean out the choke starting circuit,once again try fuel directly in plug hole,shoud get some sort of fire

[wordslinger]

...i was running about 50 mph when it shut down...

..is there a timing to the spark that i could check out??

still, i'm wondering why everything is so dry...

[art]

It's magic Ha!When you put the choke down it opens another port on to the intake side of the carb bypassing the slide and jets I think it straight fuel the vacume line is next in line on the intake side.Once fired it will draw through the airfilter side,this sound like where your backed up there is not enouph vacume to draw from the rest of the carb without fire.

[wordslinger]

...but why would that cause it to shut down at 50 mph.....

[art]

Didn't relise you were running when it happened.your cdi and flywheel are your only timing there is a spot on the flywheel that triggers the fireing time and don't think you can change without some machine work or special cdi setup.Try your a50 cdi and look at the vacume lines,my guess is a line poped off or the cdi is crapping out(no longer fireing in time)Being dry is still on the start circuit,I would think

[sidthesloth]

Sounds like you are suffering what brings a lot of people to this forum. With regards to what Art is saying about spark timing, there is a thread about that subject in the zx50 section, I think the author was asking about his engine running backwards. With my zx50 it would be a bitch to start when warm, but not shut down. My guess would be cdi, but you have spark. Since having mine set up with this cyl. kit it is now starting ok, so I put the previous hard starts down to worn rings in my old kit. Though it felt to be ok with compression something that Thebatman was told sounded strange to me at first, "good top compression poor bottom compression", to me that sounds like enough compression to run but not good enough vaccuum to pull the fuel through the carb. How was your scoot starting before this happened? Sorry if I am ranting a bit.

[wordslinger]

...it was starting great most of the time, but every once in a while, when it was cold, i wuld have to remover the filter and close off the carb's intake side with a piece of cardboard..take it off, fuel dripping out the carb, then it would fire right up...

..this all began when i snapped the firrst belt...lost some powerr then, and thought it was a split reed...


..this time, i was just running along when it shut down...thot it was another belt, just from the way it reacted...

..opened the cvt, and belt's fine...

..the dryness of the top of the piston and spark plug troubles me..like i'm not gtting fuel into the combustion chamber...

[sidthesloth]

Maybe time to remove the head and have a look at the bore, the good part about two strokes. no cams, chains, push rods, rockers....

[Hoolander2]

Leak in the crankcase somewhere.  No vacuum on the upstroke means no sucking on the carb -- thus the dry spark plug.  Also would account for the hissing, loss of power, etc. You'd still feel compression when turning engine over but maybe not as much.  If it's that, your leak must've gone from small to bigger over time.  A compression check at the spark plug hole would not necessarily diagnose it.  Gotta do a leak down test.  Or it's possible you may find it by looking over the crank case from every possible angle. 

I diagnosed a crank case leak one time by observing tiny fuel/oil bubbles coming out the case gasket just after engine shut off.   

Don't know about yours but some 2 strokes have a check valve somewhere on the crankcase.  They can go bad or get dirty. 

[Hoolander2]

I'd look at the vacuum lines like Art suggests first though.  That would account for all of it.