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Have you ever spoken to the actual engineers from the Yamaha factory that designed the YZ engines about the topic of break in on new YZ 2-strokes? I have. Summary - what you read in an owner's manual is not necessarily there because the people who designed the bike actually think it's required. Ever read some of the ludicrous things like "remove piston after 1 heat cycle, inspect for score marks and remove as needed".
At the end of the day, by your logic we should change the name of this forum to "owner's manual quotes" and just sit here passing owner's manual info back and forth. Or maybe we could split it in two and have an owner's manual quote subforum and a Hillbilly knowledge subforum.
With the KTM 690 engines, KTM would say “break it in gently. Idling is OK, etc”
This would often lead to terrible “Ring seal” - high oil consumption and reduced performance. But guess what? KTM would just declare “insane” oil consumption as “within spec”. (From memory 100ml/1000km was “ok”). So no claim.
The gentle break in was surly better for cams etc, and less likely to cause a warranty claim. Evenif the engine was a bit “marginal” to begin with, but no enthusiast (the only people who buy these bikes) would be happy with the result.
If I was paying for warranty claims on YZ125s, I’d recommend rich jetting and 15:1 for break in. Then rich jetting and 30:1 from the second tank. Plugs and “oiled up” engines aren’t warranty claims.
If I had a YZ125, I’d run it in with the stock jetting and 30:1. I would ride it as intended, and avoid idling at all costs, and constant light loads as much as possible. Then try for the best jetting I could find. (Probably leaner than stock)
It’s your bike - do what you want.
Both have stock jetting and were broke in at the same elevation setting. Using the 15:1 the bikes consumed at least a dozen plugs and seem to continue to do so even a year later on 30:1.
The bike that went straight to 32:1 is running great so far on OEM plug (it's also ridden harder so that could be a lot of the issue).
BUT
Yamalube 2R up to 2018 (I think) has viscosity @40°C - 55 cst @100°C - 8,5 cst @150°C - 3,56 cst @200°C - 2,00 cst
Yamalube 2R from 2018 (maybe ENEOS) has @40°C - 169 cst @100°C - 19,6 cst @150°C - 7,09 cst @200°C - 3,61 cst
So up to 2018 was 2R pre-diluted !!! Now they use pre-mix only - 100% synthetic oil with esters with almost double viscosity and no changes in manual. Link below is for catalogue Yamalube 2019. 2R recommended 50:1 same as Motul 800.
https://www.yamaha-motor.eu/content/dam/fi-esitteet/20-068_2020_YAMALUB…
So for me, if manual say 30:1 and 15:1 - with 100% synth ester base oils you can use it 50:1 and 25:1 for break-in. More viscosity stronger oil film which protect parts.
Average numbers of @100°C @150°C and @200°C OLD 2R 4,686 (30:1) if you want same number with NEW 2R you can mix aorund 60:1 with same result. First number @40°C is not critical in this application because cylinder head temperature is around 200 - 240°C (water cooled).
So why Yamaha do not change manual numbers when change Yamalube 2R supplier?
Now does that count as a break in? No.
Do I break my bikes in per their recommendation? Also no. I’ve done my fair share of them, and two or four stroke I run the fuel and oil I plan on running, do a moto or two at half to 3/4 pace then drop the oil (and filter if applicable) and from there on out run it as you normally would.
Am I an engineer? No, but I’ve done every new bike I’ve owned this way, and sent hundreds if not thousands out with customers and never had an issue. That’s just what this one mechanic has seen.
Why not? Because sometimes what is written in the owner's manual is wrong, and not what 99% of employees of that corporation, including the engineers who designed the product, know to be correct.
Looks the same smells the same and smells the same out the exhaust
Yamalube 2R @40°C 169 @100°C 19,6 @150°C 7,09 @200°C 3,61
Motul 800 Off Road @40°C 120,2 @100°C 15,5 @150°C 5,89 @200°C 3,10
Motul 800 Road @40°C 152 @100°C 18,7 @150°C 6,92 @200°C 3,56
Motul Kart Grand Prix @40°C 135 @100°C 16,9 @150°C 6,33 @200°C 3,29
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