YZ 125 D specs & adjustments re:servicing

[enzo906]

Hi Guys
Anyone still have a manual with things like how much oil in the forks, engine etc
and chain adjustment, standard sprokets (12,51 from memory but I am old now)
any other stuff that comes in handy for servicing bike.

Also Float height might come in handy too.

Thanks again

[IT400C]

Forks:  15 weight, 181mm from top, 14psi recommended
gearbox:  650cc
sprockets:  12/51

Jetting:
main   270
needle jet   P-8
Needle/position   GF22-3
cutaway   3.0
pilot   60
air jet   2.0
starter jet   80
air screw   3/4 of a turn out
float level   24mm

Chain length   100 links

Plug   Champion N-59G/0.6mm
Timing  1.2 +- 0.15mm BTDC

[enzo906]

IT 400C
your a legend....no pun intended.

Thanks

Any idea on porting other than raise the curve 1.5mm on top of exhaust, clean / smooth botom of inlet tract, open scavenging ports at base of barrell to meet crancases, thinner Head gasket.

That is all I can remeber from 1977, I am sure you can do more without making the bike less rideable like the 34mm Carby from the 76 X model did.

Got Any info?

[IT400C]

Yup, from the YMUS factory support wrench report..

36mm carb from the X
main jet   300-310
needle jet   Q2
Needle   6F15-2
slide   3.0
Pilot   40
air jet   2.0
air screw   1 1/4 turns out

raise exhaust port 1.5mm  - but not 1.5 mm over entire width of exhaust port:
0mm at outer edges, 1.5mm at middle - in a smooth arc.

Lower bottom edge of inlet port 2mm for entire width - match back into area around lower reed.

Mill 0.2mm off head, but make sure you still have 0.7mm clearance to piston at outer edge of squish..

This is all supposedly worth 2hp and another 1000 rpm..   

Oh, and also make sure you match your exhaust gasket apparently..   

[Nathan S]

Exhaust port is plenty high enough already - too high, even... Don't touch it!

The 125E exhaust pipe gives it a bit more midrange with no apparent downsides. Pretty sure a larger diameter stinger would be a help on either pipe (been a while since I paid attention to D/E stuff).
The  E head is also an improvement, but is not legal for Pre-78. A modern combustion chamber shape would be a big improvement to either head.

A modern ignition would be a big help, preferably one with an external rotor ignition. Mid-90s KX125 looks like it would go in easily with a custom stator plate.

Modern reed petals couldn't hurt.

I don't think the 34mm carb was the source of the 125X's peakiness - my X has a ported C barrel & the stock 34mm carb, and is beautiful to ride.

Don't forget the suspension! A re-oil/regas on the shock will make a huge improvement, and is only the tip of the iceberg... Based on how much nicer an E handles, I figure an alloy DG swingarm is well worthwhile (I own a DG swingarm for my D - but haven't fitted it yet).

[IT400C]

Hey enzo906,

Shoot me your email address and I'll send you the relevent PDF's.  A couple of Yamaha Motor Technical Bulletins (gearshift, and chain guide/chain tensioner), a Technical Update, and a couple of Yamaha Motors US wrench report letters to Yamaha Factory Support Riders.

Tony.

[Ozadvntr]

Hi Tony,
Please send them to me.

Mick