I always assumed the 1975 RD350 was the most technologically advanced and peak of development before RD400 introduced. Maybe I was just biased by how much I like the Orange/Black color scheme 
I do know stock main jets are smaller on the 1975 and assumed it was forced to run leaner due to USA smog BS or something- but don't know if Yamaha did that with performance in mind?
Sometime ago I was told by a former local (in SoCal) Yamaha Service Manager I knew through VMX racing that the 1974 RD350 was actually the best of the 3 years performance wise stock. Any verifiable truth behind his opinion? If true what are the differences that make the 1974 superior?
I do know stock main jets are smaller on the 1975 and assumed it was forced to run leaner due to USA smog BS or something- but don't know if Yamaha did that with performance in mind? Sometime ago I was told by a former local (in SoCal) Yamaha Service Manager I knew through VMX racing that the 1974 RD350 was actually the best of the 3 years performance wise stock. Any verifiable truth behind his opinion? If true what are the differences that make the 1974 superior?