need help out of ideas

[big mac]

after buying a k reg 301 all seemed fine thought I only needed to swap a split inlet manifold . after trying to set the carb for about a month and cleaning it god knows how many times im out of ideas . I've changed the chock bung and fitted a new slider also ive had the needle in 3 different heights . sprayed carb cleaner round the manifold inlet to check for leaks all seem good and the plug colour looks fine.
the symptoms are it wont tick over there's no adjustment it go's from no tick over to revving its nuts of when trying to adjust an when riding it accelerates fine but when in top at about 60mph it dies but if I let the revs of it picks up again if I keep the throttle open it back fires and pops .
the tank is clean and the fuel seems to flow ok I've decoked the exhaust and the fuel cap breather is fine
its a bing 84 carb
any idea's would be very much appreciated

[DAVID THOMPSON]

try gas with no ethanol
my rt125 runs like crap on the junk
if the 301 has a reed valve is it ok
not that familiar with the 2 stroke mz bikes
dave

[MZCountryRider]

Bad crankshaft seals?

[big mac]

next job is crank seal
cheers for that ordering as we speak
one more thing are they hard to fit

[therealche]

Do you want to try another carb before you start ripping the motor apart? Ive got a 301 Bing here and I'll send it to you for the postage for you to try out, If it makes a difference I'll arm wrestle you for a price to keep it

[big mac]

that would be great
have sent you pm

[neddyo]

Has anyone swapped the ES 250/2 carby for a Bing, is it a good idea?
I'm getting a bit bored with my original carb ( I have an arthritic hip), it's not a good starter but ok when
it's finally going.
Nick.