this may sound really stupid.....but check to see if your spark arrestor is clogged. i bought the r i have now and it would bog and not rev, which is why i got it so cheap. the arrestor was so clogged you couldnt see through the screen
As posted by everyone else; all good starting points for you to check. To recap:
Clean carb, jets, check needle clip, ect...
Clean Pet-Cock & fuel tank
Make sure fuel is flowing to carb easily
Check Reeds for broken pedals or cracks
Clean Muffler, replace packing
Clean all electrical contacts, connectors, wires...
Check compression, should be above 160 lbs
Change spark Plug, gap at .020"
Check vent line at top of tank
What is your current engine, pipe, carb set-up, and what jetting do you have? Fuel type?
I found out my problem by accident. I got slap happy and wanted to start my fresh engine right away so I did without the arrestor on. It ran fine. I shut it off and pit the scilencer/arrestor on and it wouldn't rev at all. I kind of got lucky cause I really would not have thought to look at the arrestor bit from now on I'll always check it if there's a problem
This info came in handy Yesterday. Last year my buddies bike was bogging bad whenever he would rev it up, to the point of almost dying. I figured he needed a new top end or a new CDI. We tore down a few months ago and sent out for a fresh bore and piston, although it didn't look bad. We put back together and it was doing the same thing. Put a new CDI and coil...same. I did a quick search on google and came across this discussion and decided to check out the silencer. We drilled the rivets and pulled apart and there was a huge glob of RTV stuck inside. Put back together and it fixed his issue.