13/50 120 link

Just bought a wr250x it came with a brand new r3 o ring chain (120 link), 13t front and a 50t rear. Will not be using the 50t and looking to either order the stock 42 or go up to a 45. My question is will the r3 120 link chain work with either the 42 or 45 rear? Can it just be cut?

Also with 13/45 will I need a healer?

Thanks guys

* I will be putting the 50t for sale if anyone is interested

A 120 link chain will have to be cut down for any of the combinations you mention. For example, I run 112 links with 13/51 sprockets on my WR250R. Some riders aren't confident in selecting the specific chain length they'll need so they order the longest available for the same price and just cut it down.

With stock gearing the speedometer reads about 7% higher than actual speed. (This is apparently intentional by Yamaha.) The speedometer sensor is in the gearbox, so any sprocket combinations resulting in higher gearing than stock will increase the speedometer error. Tire choices with different circumference than stock tires will also affect speedometer accuracy. All can be corrected with a speedo healer.