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My 94' RM80 was faster than that 93' YZ. They were terrible.

I had one on a yz250. Couldn't tell the difference between the maps or from stock. Long time ago, was a beginner back then!

This one has porting, head work, reeds, exhaust, aftermarket ignition and stic block fitted, and revs to the moon! Love this bike and great fun to ride, but no comparison to my 2019 TC125 with the same mods, and the gearbox is a real weak point on it. If I was to do it again I’d have kept the RM stock and built up a steel frame YZ125 with modern SSS suspension, they’re the best mix of old-school feel with good performance and parts availability

Have you done a leak down test (either before or after the rebuild)? That's where I'd start (assuming it's not a mis-routed throttle cable or something like that). Sure sounds a lot like an air leak. What does your plug look like after you've ridden it?

+1 on the leakdown test, I have had RM125”s that leak air right through the cases due to porosity….. search 2t leak down test on Utube…this should be done after any rebuild….other things to check, as stated: throttle cable routing, carb slide hanging up due to wear, partially clogged jets, worn carb orings/ gaskets.

Dude, the STIC Super X PWK 38/40mm carb is magic for small bores. The fuel uptake right off idle is very aggressive and it creates a cooled vaporous mix. I know 125 riders that have removed the less potent meter block version. The power delivery character is linear, but it is abrupt and will pull like a ported big-bore kit with more over-rev. The peak HP has a broader RPM range, so the shift point is much less critical. On trails it can be short shifted and not sign off, just keeps pulling without clutch input. No problem running a...

I raced RM's back then and remember the 01' being way "funner" stock to ride than my 99' because it was pipey and made to be revved to the moon. Saying that, can't go wrong with TMR, but i'd talk with Lynks Racing. He arguably builds the best small bore engines in the amateur scene. On top of that, was with Bills Pipe/Primal Impulse back in the day and learned those engines from Jeff Springman.

As mentioned, talk to someone like TMR. When rebuilding my 98 RM125, at first I was set on leaving it as a 125 but he informed me going to 134 or 144 setup would be at least 5hp more. Secondly, I had a few early 2000s CR 125s which people love to bag on as having 3hp. My point of bringing those up is if you find where the meat of the power is on your particular bike (even if it isn't that MEATY) and shift close to perfectly, they rip ok and can still be a blast on basically...

The G2 quick turn for two strokes will reduce the amount of turn on the throttle slightly. I have them on all of my 2 strokes and swear by them. It is basically a modified domino throttle (like the older KTM's and 90's CR's), with a larger aluminum throttle tube/cam. sort of like putting a zip tie around a stock throttle cam. But if you can make something for less money, i'm all for it.

Tom Morgan will make that engine as good as it can be….but never be as good as a newer 125…if you want an impressive older 125, pick up a 93-97 CR125, those HPP engines were dam good…I love riding my 93 Cr125, not much bottom but mid range & top end are strong…

There's one solution to make the 2000 RM faster than a YZ125...

Nothing that you can bolt onto it will make it as fast as a newer YZ125. The 2000 YZ125 had a better motor than the 2000 RM, and Yamaha has made slow but steady improvements since. There are things you can do to help it though. Checking the squish clearance would be a good start. Make sure the powervalve is functioning properly, and advance the ignition timing slightly. And of course jetting - if the main jet is too rich, it will kill top end power. Beyond that, if you are looking for more mid and top end - head...

Will do! Looking to get out on the bike and have a proper 'ride test' in the next 2 weeks. I know it works fitted in the workshop, but I want to prove it in actual use before I potentially offer it up to people. I'm confident it will be a nice little gain though. The only real/easy option is the G2 'Quick Turn' throttle, but I don't think that system reduces the amount of turn, it just speeds up the cable travel in the initial throttle opening. Which will help a little, but at a very steep price $$$

My friends and I all love the results we got from the STIC metering block, both in 150sx and YZ250 - I'm pretty confident it would help an RM125 too! Throttle cam sounds interesting Russ, nice work.