I have had this bike(1973 rv125) for about 10 year and have been tinkering with it for years. The bike starts, idles and revs fine without a load but when riding the bike it falls on its face when you rev them motor, It does not mater where I have the needle jet or if I try to choke it when it is having the problem. What can I try next? I have also checked the intake and exhaust and everything is clean. I have had the carb apart and cleaned may times and never any different results. Could it be something in the ignition? Perhaps a bad 6v battery, condenser, coil? The point gap seems fine.
Engine missing and bogging when revving, Idles fine
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Hello,
it sounds like the Main Jet is too smal.
You need a 105 Main Jet
And a new Jet needle!
Both Parts Mikuni. Don´t use replica Parts, only original!
And replace your Air filter.
This is how the Engine should run.
Good Luck
Peter
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Thanks for the reply. That is what I was thinking also. I cleaned the carb more than once and it seems to make no difference. I have also changed the air filter and verified no restrictions in the exhaust. The jet is correct and regardless of the needle position I have the same problem. I have also tried messing with the choke while driving and it makes no difference. Is there anything in the ignition that might have the same symptoms??