Help! DT250 won’t accept more than 1/2 throttle

 

Hello, newbie here.  

Just getting into motorcycles again after a long absense.  I’ve
purchased a couple of old 2-stroke enduros that had been sitting for a
while and were non-running.  One is a 1972 Yamaha DT250 with less than
1600 original miles.  Very good compression, going to be a very nice
bike.  I cleaned the carb, contacts on the points and new plug.
Started up and runs great as long as you don’t give it more than 1/2
throttle.  When riding the bike, it will bog down and sputter once
4500rpms is achieved.   So, bottom line is it runs great unless either
of two conditions are met: (1) more than 1/2 throttle  (2) 4500 or so
RPM’s.

Air filter is not the problem.
New plugs
Adjusted the point gap
cleaned carb (twice)

What am I missing?  What could be causing this?

Stange thing is, the other bike I bought from another person does the
exact same thing.  It’s a 1974 MT250 Elsinore (2-stroke as well).  

I’m stumped but I really want to get these bikes running properly and
feel the 2-stroke power!

Thank you for your time and any solutions provided...

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check the books. some of those enduros have VERY narrow
power bands. but 4500 seems low, 9k is more normal.
check the kets are seated and correct and that ALL the
gaskets on the carbs are sir tight, especialy between the
carb and cylinder.

 



It's a 2 stroke. The exhaust is clogged up. Remove the baffle and see all of
the spooge. Clean it by burning it with a torch. Sometimes you also need to
remove the complete exhaust pie and burn it clean too.

Tom.