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1979 RM100/125 https://vintagedirtbikeforums.alp-sys.com/viewtopic.php?f=29&t=2616	Page 1 of 1

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Author:	mbwarhorse [ Fri Mar 12, 2010 7:51 pm ]
Post subject:	1979 RM100/125
Hi, all..... I'm new to the forum so I'm sure this question gets asked ALOT!!!! My son & I are restoring a 1979 RM100 for him to ride. I've dug around a tad & am wondering of the differences between the 100 & the 125. From what I've been able to learn is the only difference is the bore.... I assume the carb was rejetted or even different but I cant find any reference to that. Can any of you verify or add to what I've found? Can the 100 cylinder be punched out to accept the 125 piston? My son is pushing 130lbs & I would like to get as much from this sweet old machine as possible. Ive never been on one so I have no idea of how it performed. I'd hate to have him work so hard on a restoration & be unhappy with its performance. Thanks guys!! Craig

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Author:	Loydee [ Sun Mar 21, 2010 4:06 pm ]
Post subject:	Re: 1979 RM100/125
Hi I have an Rm100/125 hybrid. The main physical differences are the 125 has an alloy swingarm,longer shocks,longer/thicker diameter forks and larger front brake. I have all these fitted on my RM100 N/T model. The engines are not a simple overbore. The 100 has 50mm bore and stroke, the 125 54mm bore & stroke. So to upgrade to 125 you need the crank,barrel piston and head. On the 79/80 models the 125 crank fits in the 100 cases, but not on the 77/78 . This has been covered in more detail on the ozvmx forum. From 79 to 80 the carb went up from 30 to 32mm. I have a 32mm on my 79 engine and seems fine. For a few more ccs you could maybe put a 125 piston in the 100 jug as there seems plenty of material there to bore. Attachments: File comment: Low cost racer £300/$500 ! 101_0659_800x600.jpg [ 75.51 KiB | Viewed 6195 times ]

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