Its not, You should be able to pull the throttle wide open & that thing just keep climbing till it needs a new gear. I cant tell mine falls off when it hits wide open.. nope, it dont. Now, whuts th answer? I dunno, but someone will come along & toss you a bone.

Weak spark or fuel/air issue.    When you hit the throttle, the bike should jump.  But,  if something is wrong in either,  you can get the "BLAH" when you hit the throttle.  

1) Weak spark, check sparkplug and if you haven't put a new one in, do it.  Std plug is cheap $2-$4.   Check wire both the HV wire and the connectors on the 2 low volt wires on the coil.  

2) Fuel/Air,  check air filter.  Check spark-plug color for too rich -too lean. (Black, tan, white???)  .  Check for an air leak in intake manifold or carb.   Is the carb clean???  Like Verslagen said too, does the slide move easily?  Also, a vacuum leak could make slide move slow/weakly.

What size main jet do you have in the carb?  
Too large a main jet will cause the very symptom you describe.

Brad_THMP3R wrote on 08/24/08 at 18:41:38:


I appreciate your enthusiastic support but the other suggestions are just as valid.  I was just adding another idea to the pile.  Checking each item mentioned in a step by step basis is the only way we can be sure what the actual cause... or causes ... are.
When getting an older used bike it is not uncommon to find several issues that need attention.

Hopefully,  Mattdw will be able to isolate his probems and get this fixed without futher problems coming out.