Alright, so this might take a bit to explain but I think someone can answer it for me.  Last year, I didn't know anything about dirtbikes really, and my friend got a 97 RM125, and I'm not sure what mods were done to it except for the fact that I am certain it didn't have the stock carb, and it had a full pro circuit exhaust. Also, the bottom end of the motor on his bike was shaped differently than the one on the other bikes i'm about to describe.  He had what looks like ( I think) a Keihin PWK Airstriker 38mm, which would explain why he fouled a plug almost every ride we went on. I had a 00 XR200. Later that year, my other friend, bought another 97 RM125, which (I think) was completely stock, except for a full FMF exhaust.. The first friend's bike had literally twice as much or MORE bottom end than my other friends new bike. Now that I know quite a bit more about bikes and have ridden a lot of them, I will say the original 97 RM125 had just as much bottom end as a stock 98 KX250. The other thing is that the rm125 that had a ton of power had the stock 125 bore, and the new one had a 134 big bore kit and still did not even compare in bottom end. Gearing was stock on both bikes.  Now, just recently I have picked up an 01 CR125, which has vforce reeds, stock bore, fmf fatty, short silencer, and stock gearing.  My friends bike (the powerful one) is still easily twice as powerful as mine in bottom end, and I would really like to know how he achieved that. My bike has a mikuni 36mm carb (stock)...can a different carb really make THAT much difference? What the hell else could have been done to that bike to make it so powerful in the bottom end? and it didn't lose any top end either, it would easily beat the other rm125 in a drag, top speed and acceleration. Every 125 I have ridden since then has been comparable to mine in power, but I really want to know what to do to get that bottom end like he had. Is it possible that his bike had an entirely different bottom end in it somehow? For example, the water pump was not in the same location as it was on the other 97 125, which we always found to be odd. Anything will help, Thanks! and it's not that my bike doesn't run well, because it does in fact it's absolutely mint as far as i'm concerned and pulls very hard when in the powerband.

If you want more bottom end either get a smaller sprocket on the front or a bigger sprocket on the back, this will affect your top end speed though, also fmf and pro  circuit make pipes and silencers that will increase bottom end

The 01 is known to be slow in the bottom end its something your going to have to accept, but there are some things you can do to improve it. I highly recommend reading this; http://twostrokemoto...01-honda-cr125/

All things being equal your bike with the 36mm carb should have more lowend than your buddies with the 38mm. The problem is, the 01' CR125 is a turd. How do I know they're turds? That's my 01' CR125 in the article.

Wow, you sure do have a story there.  A lot of it sounds to be based on thoughts and feelings.  As far as the engines being shaped different, that means they are different.  (could it have been a 250cc engine?  I know you mentioned it was a stock bore, are you sure?)  There are not any mechanical tricks in the world that will make a stock bore and stroke 125cc make as much power as a stock 250cc.  (considering we are talking about two mass manufactured dirt bikes)

There are a lot of extensive tricks that can be done to make the 125 run much better but short of changing the bore and stroke and some major chemistry in the fuel tank, you are not going to equal the power of a 250, even on the bottom end of the power curve.

Most likely the reason your buddy's bike was fouling plugs was due to improper jetting not just throat size.  With that said there are a lot of good ways to get more HP out of your bike.  I can't remember if your bike is a case reed setup, if it is then you will need to give the entire engine to someone like Pro-Circuit and let them bore it, stroke it, adjust port timing, massage the ports, raise compression ratio, bore the carb. and add a little flywheel weight.  After somewhere around 2 grand you will have a fire breathing missile but it still won't make as much power as a modern KX 250 or any other manufacture's race bike for that matter.

I can only speculate on what may have been done to the one you really liked but if you are ready for more power I suggest you sell the 125 and buy a 250 2 stroke.

Hey guys, and thanks for the reply! that sure is an interesting article.... While I don't have 2 or 3 grand to spend on making my bike faster, I will definitely look into some alternative ways to gain a little power here and there.  Although that RM125 that I really loved has been sold to a friend's friend and is now sitting against a shed with a blown cylinder due to improper care, I think i'm going to ask him and take a look at it so I can see what's been done to it. And there is no way it was a 250 motor, I replaced the piston myself and it was a 54mm. Thanks for all the replies!

If you'll do the mods we did in that article the bike really wakes up.