Power Options To Upgrade A Honda Xrm125

[i am bob]

Both good answers as well as cheap and easy to accomplish!

[robert k]

Dalidali, I would not worry much about airbox/filter and exhaust, if you don't know what you are doing you can lean out an engine easily by letting it have too much air causing a short engine life. I recommend people run an aircooled engine to the rich side rather than the lean side, as long as you don't go to far and make the plug dirty. An exhaust is unlikely to do anything for you unless you are going fast already. The exhaust is unlikely to help you at speeds encountered around town. Restrictive exhaust actually helps low end torque, also helps drivability, that is why the manufacturer put them on in the first place.

On the other side, with a larger diameter sprocket with more teeth, you are just using a bigger lever. Many people may not believe it but it probably won't hurt top end either, because you can push harder into the wind. It may also help you maintain speed when climbing a steep hill without downshifting. Gearing is linear 10% more gear 10% more power, 10% more fuel burned per given distance. There is always a tradeoff somewhere. I think you can probably go 10% bigger on the rear sprocket and still use the standard chain. It would be quick and cheap at the shop, quick to change back if you didn't like it, if you save the old sprocket. With a small bike wind resistance usually stops you for top speed, that is why even little guys hunker down when trying for top speed, it's possible that you could achieve the same top speed with the larger sprocket, maybe even go faster, albeit at a higher rpm. I think that is your best bang for the buck.

Edited September 1, 2013 by robert k

[dalidali]

Great suggestions and your take on gears/exhaust.

 

I am fully aware of the air/rich/lean mixtures on aircooled bikes.

I have a Harley at home..a 2011 V-twin Super Glide. Fuel injected. (avatar photo)

Damn they are hot!!....after much research, and the subsequent heat issues, I decided to install an electronic devise (resistors actually) that fool the brain into thinking the mix was too lean.....so this device sends the signal to the brain.....more fuel

With that richer mixture, it's just hot....not damn hot. No plug issues so far.

Coupled with an after market, less restrictive exhaust system and an aftermarket frame mounted oil cooler, it's tolerable on the heat and I would say the acceleration performance is improved...not a whole bunch but I can feel it.

 

Now if I could only adjust from 1 down/5 up on the Harley shifting, to the all down on the XRM :bash:

Edited September 1, 2013 by dalidali

[Bruce]

Now if I could only adjust from 1 down/5 up on the Harley shifting, to the all down on the XRM

 

You are not alone! I have mis shifted more than I care to admit. Most of my bikes are 1 down and 3-4-5 up in the US but then in Phils it was 4 down up to recently when I bought the Yamaha (India) 153 and back to 1 down and 4 up. Damn confusing to reprogram by brain.  

Another issue I have is that my US bike is a Suzuki Bergman 400 which is an centrifugal belt driven. No gears at all and what is the real issue is that the engine will not start unless the kick stand is UP. But in Phils, the bike starts with the stand down... so many times I drive off with locals yelling STAND at me to remind me to raise the stand.  

[joeatmanila]

Lets take it down to pure engineering.

You can do the heck of modifications on such a small engine and non complicated system. What you will get on the end is something less in some part that the original manufacturer made it.

You can get higher torque, you will loose somewhere else and so on for whatever you want to take you will have to give up something else.

[gapotwo]

Dalidali, I would not worry much about airbox/filter and exhaust, if you don't know what you are doing you can lean out an engine easily by letting it have too much air causing a short engine life. I recommend people run an aircooled engine to the rich side rather than the lean side, as long as you don't go to far and make the plug dirty. An exhaust is unlikely to do anything for you unless you are going fast already. The exhaust is unlikely to help you at speeds encountered around town. Restrictive exhaust actually helps low end torque, also helps drivability, that is why the manufacturer put them on in the first place.

On the other side, with a larger diameter sprocket with more teeth, you are just using a bigger lever. Many people may not believe it but it probably won't hurt top end either, because you can push harder into the wind. It may also help you maintain speed when climbing a steep hill without downshifting. Gearing is linear 10% more gear 10% more power, 10% more fuel burned per given distance. There is always a tradeoff somewhere. I think you can probably go 10% bigger on the rear sprocket and still use the standard chain. It would be quick and cheap at the shop, quick to change back if you didn't like it, if you save the old sprocket. With a small bike wind resistance usually stops you for top speed, that is why even little guys hunker down when trying for top speed, it's possible that you could achieve the same top speed with the larger sprocket, maybe even go faster, albeit at a higher rpm. I think that is your best bang for the buck.

Go to your local dragstrip here in the philippines, You can find one at any country road. check out the mods. on the 125 xrm drag bikes. you will find that there aint a one without a crossflow  crankcase breather.equals maximum engine cooling which reduces lean out.Ive never ran one in TEXAS but i know it is possible in the Philippines. Ever seen a 18 secound XRM 125 running on The bottle?  (NOX) ? it lives in Sta Rosa Laguna   VROOOM  EJ.