RD350 Jugs

[Gene Ungar]

I just checked and the stock gearing appears to be the same on the 250 and 350.  Both 16/40.

But, my 250 feels nearly as strong as the 350.  Both engines are fresh and the jetting is good.  They both have strong urge off the line.  The 350 is a bit more wheelie prone in first gear, but the 250 is not far behind.

I do remember taking a brief ride on a friend's new RD250 in '73.  That bike MOVED.

[m in sc]

primary gearing, crank to clutch is different. the 250 is more aggressive.

[Gene Ungar]

Ahhh, that explains it!  Thanks, Mark. 

That's a good reason not to "upgrade" to RD350 cylinders.  You would still have the short internal gearing.

[m in sc]

ive actually used 250 primary gearing on a 350, then made it up on the sprocket and chain. this slows the clutch down a bit. its nth degree stuff but it helps the motor wind up faster. just .02

[Jspooner]

I run 250 primary gearing on my RD.

[Striker1423]

I do too. Its fast. Just really screams on the highway at 75mph. Like 6600rpm.

[SUPERTUNE]

I just checked and the stock gearing appears to be the same on the 250 and 350.  Both 16/40.

But, my 250 feels nearly as strong as the 350.  Both engines are fresh and the jetting is good.  They both have strong urge off the line.  The 350 is a bit more wheelie prone in first gear, but the 250 is not far behind.

I do remember taking a brief ride on a friend's new RD250 in '73.  That bike MOVED.

Are you sure you counted right?
The stock RD fronts are a 15T sprocket, maybe has been changed from stock?
Chuck

[Gene Ungar]

I looked it up on the partzilla site, Chuck.  It showed the same 16 tooth front sprocket for both.  The website might have been wrong, of course.

[SUPERTUNE]

Must be...because stock is a 15T.
C

[m in sc]

yup. stock is 15.

[John Ritter]

its closer than you might think. just fyi, look at the transfer port duct area 250 vs 350. You can squeeze a lot of power out of a 250.

I did a 250 years ago, it would run dead even with a stock 81 LC. It was ported to death but it was definitely NOT slow. A stock 250 is really good. I wouldn't count it out.

Mark, the BMEP potential of the 250 is far greater than the 350 making them a sweetheart to modify. The 2R8 top end has the outside dimensions of a 400 so cooling is better too.

[SoCal250]

I looked it up on the partzilla site, Chuck.  It showed the same 16 tooth front sprocket for both.  The website might have been wrong, of course.

Partzilla (and other vendor sites) will usually show only the current available or most recent available part, not the original installed part from the factory. To confirm original specs you should look at Service Data from Yamaha or a vintage Yamaha Parts List
THE TECH LIBRARY »Yamaha Factory Specs and Info »Yamaha Service Data
THE TECH LIBRARY »Yamaha Factory Specs and Info »Yamaha Parts Manuals

And yes, 40/15 is stock for the RD250 & RD350

[m in sc]

its closer than you might think. just fyi, look at the transfer port duct area 250 vs 350. You can squeeze a lot of power out of a 250.

I did a 250 years ago, it would run dead even with a stock 81 LC. It was ported to death but it was definitely NOT slow. A stock 250 is really good. I wouldn't count it out.

Mark, the BMEP potential of the 250 is far greater than the 350 making them a sweetheart to modify. The 2R8 top end has the outside dimensions of a 400 so cooling is better too.

exactly, the possibilities IMHO are really (outside racing) sort of overcast by displacement desire.