What weight engine oil for a ttr 80 - 2002 Yamaha TT-R 125

do you mean trans gear oil if so you can use 80 weight oil or automatic transmission oil in a standard trans, since its getting to colder weather and will help with easier sifting in the cold weather.

you use 10w40 or 20w50 motor oil in this if you talking about engine if your talking about differential oil then its 80 weight oil.

The manual for Honda fr700 does not mention anything about gear oil as an 80/140 weight! It does say to use engine oil 10/30 or heavier 20/40-20/50 according to temp during heavy service.
see page 8 of its manual.

This is a good question. Normally, the bike calls for 80/90 weight oil but the newer HD performance engines, transmissions and primaries use a good 40 weight in all three areas. I know of quite a few people that use 40W and they all say the bikes run cooler, shift easier, better performance and better mileage.

30 weigh oiltdetergent (if available,if not regular 30 weight oil will perform also), as for the gearbox.transaxle for the tines use 80-90 weight gear lube

Yamalube or equivalent10\40,

SAE 10/40W

Hi
have your oil replace with new and make sure it is the proper weight. In cold weather old oil gells up making thiker once it warms up the pressure will go down but is not protecting you engine.

Engine Oil SE Class SAE 10W40, 10W50, 20W40, 20W50
w/Filter Change 4.0 liter
No Filter Change 3.5 liter
Level On center stand, wait 5 min, middle of window Left side of engine case cover

Final Gear Case Oil
Above 5°C API GL-5 SAE 90
Below 5°C API GL-5 SAE 80
Capacity 0.2 liter
Level Mcy vertical, to bottom thread of filler cap hole left side of rear wheel

Engine oil and trans oil are the same

80/90 wt Hypoid gear oil is used in Transfer cases and final drives