the need for speed

A question i'm sure every 125 owner asks: how to i get more speed out of my machine?

I've got a lexmoto lsm125, not a bad bike by any means but the top end is a bit lacking. As far as i'm aware the best way to get more power is an aftermarket exhaust, bigger front sprocket (top end but lack of acceleration), new air box and a bigger jet for the carb.

I've got a new exhaust in the post so that's one ticked off the list. Now i'm not an idiot but not a genius when it comes to mechanics so i'm not too sure what i need to be looking for concerning the airbox and carb jet. Starting with the airbox how much of a difference does this make? Should i be looking for a bigger or smaller airbox? and what shape?
The bigger jet also stumps me a bit. what size should i be aiming for (bearing in mind the aftermarket can, airbox and sprocket i'll hopefully be fitting)? and is it difficult fitting a new jet?
Potentially i'd like to swap the flat piston for a crowned one, but i'm not sure if this would be worth the effort/money.

Obviously i'm not expecting a step by step guide but any help would be very appreciated! and before someone suggests i bore the thing out, i'm trying to do as many reversible upgrades as possible out of fear of any mistakes (not to mention the legality and voiding of my warranty).

Ta very much for any help!!! :icon10:

All these mods are mostly nonsense other than a bigger rear sprocket will give you quicker acceleration at expense of a top end, on a 125 I wouldn't want to peak out at less than 65 mph anyhow. You'll probably rob your bike of some or even all of its torque 99% of the time. If you really know your stuff you can get more hp but then you'd likely be a mechanical engineer with access to a dyno. Certainly the bike will sound faster, but it's nearly always psychological. Done all this about 10 times, never again without a dyno.

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Originally Posted by ZMC888

All these mods are mostly nonsense other than a bigger rear sprocket will give you quicker acceleration at expense of a top end, on a 125 I wouldn't want to peak out at less than 65 mph anyhow. You'll probably rob your bike of some or even all of its torque 99% of the time. If you really know your stuff you can get more hp but then you'd likely be a mechanical engineer with access to a dyno. Certainly the bike will sound faster, but it's nearly always psychological. Done all this about 10 times, never again without a dyno.

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I'm just going by what I've read or been told. In theory these mods combined should work but I really don't know.
Any one else agree with this guy?

Just put 57.4mm kit http://item.taobao.com/item.htm?id=14125240600 on it.

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Originally Posted by humanbeing

Just put 57.4mm kit http://item.taobao.com/item.htm?id=14125240600 on it.

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According to Google that costs £1.38. Surely that can't be right? Is ¥201.00 two hundred or twenty thousand?
Also, are these as easy to fit as they appear or would I need specialist tools and knowledge?

the kit: 201 + domestic shipping: 20 (CNY to GBP ~ £23.??) | agent: 10% of (Item Cost+Domestic shipping fees) CNY35 minimum + Int'l shpping (weights 1.? kg to 2.? kg )

There's some cheaper shipping option in market. Ask the agent for details.
For example: http://www.sendfromchina.com/pages/i...tle/uroexpress (frowarder ships to UK 1st. Royal mail 's rate can't beated up. )

I wasn't complaining that its too expensive! Its incredibly cheap, too cheap to trust almost. I understand china can pump out some cheap products but surely just the metal (let alone actually making the thing) costs more than £1.38. I'm presuming you can vouch for the quality, I'd hate to replace such an important part of my bike with something which has been badly made.

Speedy honestly trying to make a bike faster without a dyno is like trying to ride through a city center at exactly 30mph without a speedo, possible, but unlikely you'll get it right. So you're probably wondering 'how/why does it go wrong?' What happens is that after you have re-jetted and changed the air box or put on a clip-on air filter to get more air out of the bike you need to change the muffler, this is where it is easy to fail without a dyno. The temptation is to run the exhaust straight through but on a dyno it has been proven that if you are lucky you maybe gain a tad of horsepower but could lose huge chunks of torque, OK if you are a track racer and nail the throttle open constantly maybe it's OK, however on a real road with real traffic you need your torque band for those times when you are riding at less than 100% such as coming off the lights and coming out of slower corners. Basically all street bikes need some kind of exhaust restriction to keep their torque band, however when you change the fueling elsewhere on the bike you need a bespoke exhaust muffler exactly for the needs of your bike.

If gaining that bit more speed would result in a major loss of torque it'd not be worth it. I haven't got much torque as it is and enjoy testing my road tyres off road where I can, so I think I'd end up being dissatisfied with the results.
As I said I've got a new can in the post but its a 35mm pit bike exhaust seemingly made for Chinese 125s/PEDs so I don't think it'll make a major difference. I was considering replacing the flat piston for a crowned one, you think I'd get a noticeable change (and not at the cost of that beloved torque)?
While we're at it, is there any changes I could make for more power? I don't really want to increase the bore (at least not for a while) and everything else I'd considered seems to lose more than I'd gain.

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Originally Posted by speedyspeedyboy

...costs more than £1.38...

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http://en.wikipedia.org/wiki/%C2%A5 CNY & JPY shares the SAME currency sign!!!

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Originally Posted by humanbeing

http://en.wikipedia.org/wiki/%C2%A5 CNY & JPY shares the SAME currency sign!!!

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Haha that explains it! I'll keep that site saved for now, have a proper look when I'm ready to make such as drastic change. Thanks.

I have installed a 150cc bore kit, and top up the max speed to 110kph (GPS tested).
more cc is what you need.

Speedy, try reading up or finding some youtube videos where there are proven results, there may be something out there where someone has dyno tested a 125 and possibly made it more powerful by changing the fueling and proven it on a dyno, if you then replicated those procedures it might work for you. There is a particularly interesting video with some guys trying different pipes on a Harley connected to a dyno. Basically they found that by putting on the very popular 'drag pipes' which are straight-thru the bike lost some power and nearly all it's torque, then welding in a coin into the pipes to make a little restriction boosted the torque back up to nearly half a stock pipe.

I've never looked into changing a piston before, not sure about that one.

My logic would be that by increasing the airflow and fuel mix by a certain percentage you would need a muffler to be less restrictive by that amount too. At the end of the day don't worry about this stuff too much riding bikes is all about having fun and playing about with the way your bike runs can teach you a lot.

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Originally Posted by td_ref

I have installed a 150cc bore kit, and top up the max speed to 110kph (GPS tested).
more cc is what you need.

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Well that's rubbish because mine sits at 62mph, head down on flat 70mph, and I've had 85mph down a massive hill. People seem to always claim top ends are s bit lower that what they are.

And zmc888: you seem to love dynos. Ta for the advice though. Riding is and always will be the best bit about having a bike, but as I improve how I ride I want to spend some time and money and improve what my bikes capable of.

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Originally Posted by speedyspeedyboy

Well that's rubbish because mine sits at 62mph, head down on flat 70mph, and I've had 85mph down a massive hill. People seem to always claim top ends are s bit lower that what they are.

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If those figure read from speedometer, the actual speed should be 10-20% lower.

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Originally Posted by td_ref

If those figure read from speedometer, the actual speed should be 10-20% lower.

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If that's true it makes me sad. Why does it show at 10% increase?

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Originally Posted by speedyspeedyboy

If that's true it makes me sad. Why does it show at 10% increase?

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Welcome to the forum.

One thing you can look at doing is porting the head. Along with re jeting or milling out the jets (For people like me who cannot get jet kits for my Chinese knock off carb). Proper carb adjustment will do wonders, in my experience. Always need to remember if your going to increase the airflow in and out of your engine you need to increase the amount of fuel. I've had rather good success with the mods I've done to my Baja DR125. Messing around with the sprockets is definitely something worth looking into, my bike from factory is geared extremely low. Figure in the range of 3.73ish final drive. I believe I had a 15 tooth on the front and a 56 on the rear, changed out the rear 56 tooth sprocket for a 43 did wonders for my top end (yes you do loose torque). However in my case I didn't loose a ton of low end power because the bike was geared extremely low anyways. Part of the reason the factory did this was to limit the top speed. You'll have to mess around with the sprockets to find out which setup works best for your driving conditions. Just remember not to go too low, otherwise you'll end up going slower in 5th gear than in 4th, and say goodbye to any torque lol.


Total mods I've done:

FMF slip on muffler
High Flow Air filter
Ported Intake and Exhaust (Maybe 1.25 to1.75mm at most)
High performance coil (Its hot orange, so it must be badass)
Performance CDI
Adjustment & Re jetted carb
Changed final drive gear from 3.73 to 2.86

ive fitted a performance exhaust, swounds go and cars move out the way more the filtering tho trafic. i fitted cone air filter sounded faster but wasnt it just hit the rev limiter sooner than normal(rev counter brocken) so i fitted bigger jets (100) now it runs too rich and adjusting the card dosent seeem to work at all. so im going to just keep the exhaust now a fuck the rest off.

Attachment 13277
Just an update.
So far I've fitted:
Yoshimurra rip off pit bike end can £35
16t front sprocket £9
Renthal fat bars £40

The cheap exhaust is sick. Not a perfect fit, but only 2mm out. Will get some wading soon. The sprocket is OK. I got it to reduce the strain on the beast; sitting at 7400rpm in 5th at 60mph, instead of 8500rpm. But there isn't enough power to back up the higher ratiod 5th gear, unless I'm going downhill or with my head down.