Hi folks,
 I was wondering if anyone knows if the DT100 and MX100 of the same era share parts with the RS100? If so it would be great to have those options for aftermarket parts too. What websites do you guys like to use?

Thanks and I should have some more dumb questions before long

Yamaha shared a lot of parts across models... not sure what specific parts you're asking about. You can check part numbers on places like Partzilla and CMSNL to see what is identical.

The USA RT100 from the 1990's might be a source of some parts too... Yamaha stripped down a 100cc street model still sold in other parts of the world and sold it here as an off road trail bike... some RT100 parts are identical to the 74-on DT100 (sometimes with different part numbers though) and probably would work on the RS100.

There really isn't going to be much "aftermarket" in the US for an almost 50 year old 100cc bike... there wasn't much of anything available even when the bike was new! We didn't have restrictive laws or taxes on legal engine size here like they did in other countries so if you wanted to go faster you'd simply buy a bigger bike.

The saving grace may be the small bikes were and are very popular in places like Thailand, Philippines, Singapore, Indonesia, etc and it wouldn't be surprising if Yamaha sold the same basic 100cc bike in parts of the world for decades... so there may be a lot of parts (stock and aftermarket) still available in other parts of the world.

Lt2/3 share parts between the Rt and Dt. Cmsnl is the only place to view 72/73 LT diagrams. I know the kick parts are interchangeable with LT and Rs as there was a guy at barber vintage that had bought couple kick gears off eBay foot Dt. Not the same as LT and Rs. Write your part numbers down and research.

The RT100 is far more similar to the redesigned 74-on DT100 than the earlier design LT2/LT3. 

Looking at the RS100 engine...  it appears Yamaha based it on the earlier LT2/LT3 architecture.  . 



 

The RS100 i'm thinking of is very similar if not the same as my LS3 which is based on the old motor like LT2, or HT1 if you go right back. Motor shape & design changed for some models in "74 like DT100 & MX100. Gets a bit confusing around that time.