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Normal top end break in procedure you follow?

Started by RDnuTZ, September 23, 2025, 04:37:50 PM

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RDnuTZ

I do heat cycles with bike stationary. Jetting at normal specs. Start it and don't even expect an idle as top ends are usually tight, gently roll on throttle up to no more than 1/2 throttle and back down for 5 minutes then let it cool down. 2nd cycle start from cool motor and go 10 minutes rolling throttle up and down to about 3/4 throttle while occasionally holding it open at 3/4 turn for several seconds. 3rd cycle start from cool motor exercise throttle for 15 minutes to 3/4 throttle with occasional quick blips above 3/4. Let it cool, look at plug(s) and fire up again and do short test ride going through the gears with no WFO yet. I don't start tuning with jetting until it feels broken in.

What's your process?
1987 TZR250R Restricted Japan Domestic market bike (Project)
1977 RD400 (Project)
1974 RD350 (2) (Projects)
1973 RD250 (Project)
2022 Beta 300 X-Trainer, Yamaha Vintage MX, YZ (18)

m in sc

basically the same. 3 heat cycles, 1-2 short rides. recheck torque, and compression.  if compression is good.. rings are seated and its ready to go. then jet if need be.

quocle603

Do not underestimate the power of a two-stroke.

1975 Yamaha RD350 (modified), 1973 Yamaha RD350 (stock), 1971 Suzuki T500, 1981 Yamaha XS650 HS2, 1982 Honda MB5, 1980 Puch Maxi, 1979 Puch Magnum, 1993 Tomos Bullet, 2003 Malaguti Firefox F15 LC

m in sc

ive killed a motor with bad timing in less than half a mile. new. so, time really means nothing. there's no real bed in procedure w these motors, just the rings. no cam, no flat bearing surfaces, etc. 1-2 hours IMHO is ridiculous.