1972 Suzuki TS 125 Bogs Down

[fatguybp]

I just picked up this bike, and when you shift from first to second it bogs down quite a bit, like its dying and almost does if you dont switch to first again, it seems the RPMs have to be really high in order to switch without bogging.

 

[dirt bike dave]

Do you have fresh gas? A new spark plug? Is the air filter clean and not overly oiled?

Some of the old street/trail bikes had stock sprockets that were very oriented toward the street. How many teeth do are there on the sprockets? A 1 or 2 tooth smaller front sprocket or a 3 or 4 tooth larger rear sprocket would make first and second gear closer together, and might make a big difference for trail riding (you might need a longer chain if you go to a bigger rear sprocket).