New project '73 Yamaha RD250

[Striker1423]

Merry Day-After Christmas!

18 ft lbs on the head won't hurt it. Stock was I think 15.

If the bike is pulling harder in the 80's temp-wise than in the 60's, be aware that a 2T motor in the cold usually runs leaner due to the air density changing.  To check this, when riding in those lower temps, reach down and turn the choke on (safely! lol, don't get hit by Joe Turd-burglar. on his phone). If the bike starts pulling and making power, you are lean on your main jet. If it stumbles and bogs out, then the mixture is rich on the main.

Remember, Lean is Mean, but Rich is Reliable.

My guess is you have a bike running rich. But the change in emulsion tube would for sure mess with things. That's getting closer to jetting voodoo for me and I leave that to the experts on here.

[SoCal250]

Jeff,
Striker is correct. Factory recommended torque is 180 in-lbs (which is 15 ft-lbs.). I have always torqued just a little more. Cylinder nuts should always be retorqued after initial heat cycling.

From the factory Yamaha manual, RD250/RD350 1972-75 (LIT-11613-61-02):
  Cylinder head nuts should be loosened and tightened in a "cross" pattern and in progressive stages with final torque of 180 in-lbs. (2 m-kg).


FYI - I have added factory torque specs for RD model cylinder heads in the Tech Library under "Yamaha Service Data"

[so-cal-sdr200]

Thanks guys. I eventually found the torque table on page 46 of the .pdf Clymer manual.
It showed 8mm = 15-18 Ft/Lb  and 10mm = 25 - 30 Ft/Lb. I was wondering if the
studs were 8mm or 10mm, couldn't remember when it was apart.
I have an old 1/2" drive, spring loaded torque wrench that I am not super confident
in it's accuracy. Will give it a try on a larger bolt / nut set at 18ft/lb and see is it feels
close.

Next step back to the jetting.
When taking off from a stop, adding the choke seemed to improve the stumble.
Easiest would be to raise the needle one more groove. after that.....
I may go back to the 35 pilot and up the main one size more.
Cheers folks and Happy New Years.

[SoCal250]

Thanks guys. I eventually found the torque table on page 46 of the .pdf Clymer manual.
It showed 8mm = 15-18 Ft/Lb  and 10mm = 25 - 30 Ft/Lb. I was wondering if the
studs were 8mm or 10mm, couldn't remember when it was apart.
I have an old 1/2" drive, spring loaded torque wrench that I am not super confident
in it's accuracy. Will give it a try on a larger bolt / nut set at 18ft/lb and see is it feels
close.

That passage from the Clymer manual is an error. I found that too when looking through all my service manuals. That section is actually for the engine mounting bolts and it is listed on pg 15 of the factory manual. I've attached the 2 pages with the torque values.

[so-cal-sdr200]

Just thought I'd toss out the latest picture of my finished project.

Still messing around with the jetting, it ain't quite right yet.
Cheers, Jeff

[jetta90]

That's a great looking RD250!...and with the front drum brake too!
Looks very good indeed.  Hoping my long time 73 RD250 project turns out as nice as yours!
Well done...

[soonerbillz]

Excellent thread.. I learned a few things that will help me in my R5 build.
You built a beautiful bike..