Tuning A 125cc 4-Stroke

[Fozzie]

Hi, i'm looking at buying a nice little 4-stroke for my first bike just to act as a commuter and to get my experience up. The problem is that if I were to get a 125cc 4-stroke it would be barely kicking out more power than my old Aprilia RS50, which was tuned to the point it did 80mph.

The bike i'm looking at has a Yamaha TTR engine. Does anyone know how to tune these engines so that its giving hp thats in the mid- 20's. Ive got plenty of money to spend and I DONT WANT A BIGGER BIKE.

Is there anyway to change the timing of the valves? Sorry i'm a noob with 4-strokes because i've lived with 2-strokes all my life.

[Bill_on_a_bike]

Nitrous Oxide?

I've never heard of a 125 4 stroke putting out more than about 15 horse.

[Guest]

Ok personally I would save your money, pass your test and buy a bigger bike. Without big boring a TTR125 you could get a racing can and a air filter ( such as a K&N ) and upjet it obv. You could also change the sprocket size but you will loose acceleration power but gain top end.

You can buy big bore kits for the TTR 125 from here:

http://www.powroll.com/P_YAMAHA_TTR125.htm

I must add unless you know what your doing from back to front don’t even try to attempt to bore it yourself. You can bore it to a 150cc for example which includes: sleeve, forged piston, pin, rings, circlips, headgasket, basegasket but as that website said it will also require resleeving and boring your stock cylinder and rejetting which ive already mentioned doing anyway.

http://www.motorcycle.co.uk/lists/EngineWork.html

[Bill_on_a_bike]

Altohugh if you're on L plates after your CBT, big bore will make it illegal, and void your insurance. Although that does require the insurance company to bother pulling your engine apart.

[Guest]

Yep

And theres help here:

http://books.google.co.uk/books?hl=en&i ... Ng#PPA1,M1

[Fozzie]

I was talking to my uncle, who has a cbr600 and he said if I gave him a 125cc 4-stroke engine he could change the power output from 15 to 25 hp if i gave him 3 hours and £50 using nothing but tools.

I asked how and he just said two words "valve timing". Can anyone validate that this may be possible? lol

[Guest]

head skimmed and gas flowed, then reprofile the cam gave my XJR

another 18bhp then carbs and exhaust took it to extra 35bhp although it

is a big engine it is still 1/3 extra power, (105 standard)

[Fozzie]

Its so damn complicated to give a 125cc 4-stroke more power. A 2-stroke, you just put a new exhaust, carb, air filter and race reeds and the power doubles. I'm probably going to sack the idea of a 4-stroke.

[Guest]

you can get an exhaust, fit K&N filters and get some extra power but you

may need to adjust th carb mixture a bit 2

[Christophe g]

Does anybody know where I can get a 350 cc registered as a 125?

[Tinkicker]

Holy thread ressurection batman.....

Are these bots digging up all these old and well dusty threads?  I think yes.

Edited July 14, 2024 by Tinkicker

[RideWithStyles]

.

mods do you need to have a look/chat/poke?

[Tiggie]

@RideWithStyles I approved the post solely for the entertainment it will bring 

[Hairsy]

15 hours ago, Christophe g said:

Does anybody know where I can get a 350 cc registered as a 125?

 

You can register engine changes with DVLA. It's not uncommon.

 

If you want a slower bike though, it's probably cheaper to just buy a 125.

 

Good luck, whatever you decide.

[S-Westerly]

1 hour ago, Hairsy said:

 

You can register engine changes with DVLA. It's not uncommon.

 

If you want a slower bike though, it's probably cheaper to just buy a 125.

 

Good luck, whatever you decide.

I don't think the OP wanted to change engine size just work the system.  Might be wrong though. 

[RideWithStyles]

Six reasons:

1 they wanted to see if they could fug the system of having a 350 engine in while it’s reg’d as a 125 - this is most likely!

2 they wanted to see if a 350 could be learner legal as a 350 by detune.

3 they want to put a 125 into a 350 frame.

4 arse hoose are filling the members list.

5 bots.

6 Tiggie is trying to mentally screw us over.

Edited July 15, 2024 by RideWithStyles
For laughs

[Mississippi Bullfrog]

I think that in our modern age any 350 has the right to self identify as a 125. 

[Fozzie]

Blimey. I was 17 when I made this post. A couple of months shy of 18. Had never owned a 4-stroke before and found the valve train a bit like black magic at the time. 

 

I was buying this at the time: 

Cheap little Spanish made bike that had Yamaha mechanicals from an old off-road bike. There was a off the shelf high performance cam/cylinder kit that took them to something like 180cc that were dirt cheap. 

Most people told me to buy a bigger bike, and I couldn't even fathom the extra insurance costs, so was getting frustrated with that being touted as the main option. I gave up on the plan as I bought a car to do the getting around duties.

 

I moved to London that November, and bought a GPX400 for a few hundred quid. Didn't like it, so essentially traded it for a CBR125, which I did like and I spent many a night in the garage doing various services it didn't need, but I wanted to learn. And is why I have a little CBR125 project in my garage now.

[m0tion]

On 31/05/2008 at 13:20, Fozzie said:

Hi, i'm looking at buying a nice little 4-stroke for my first bike just to act as a commuter and to get my experience up. The problem is that if I were to get a 125cc 4-stroke it would be barely kicking out more power than my old Aprilia RS50, which was tuned to the point it did 80mph.

 

The bike i'm looking at has a Yamaha TTR engine. Does anyone know how to tune these engines so that its giving hp thats in the mid- 20's. Ive got plenty of money to spend and I DONT WANT A BIGGER BIKE.

 

Is there anyway to change the timing of the valves? Sorry i'm a noob with 4-strokes because i've lived with 2-strokes all my life.

Hi, was just wondering how the hell you got your rs50 to go 80mph

[skyrider]

6 hours ago, m0tion said:

Hi, was just wondering how the hell you got your rs50 to go 80mph

yes neve got my fs1e to go that fast

[Tiggie]

The old rs50's were 2 stroke and produced 11bhp when unrestricted. I always wanted one but wasn't confident I could keep it running for long 

[bud]

They even do 80-90cc cylinder kits for the RS50. As they used to race them.

But 80mph on the speedo, is probably 60 real speed.

Edited February 2 by bud

[RideWithStyles]

On 02/02/2025 at 08:59, skyrider said:

yes neve got my fs1e to go that fast

When it was in the van.

[RideWithStyles]

On 02/02/2025 at 02:17, m0tion said:

Hi, was just wondering how the hell you got your rs50 to go 80mph

When it was in the van

Edited February 3 by RideWithStyles

[Grumpy Old Git]

On 16/07/2024 at 09:52, Fozzie said:

Blimey. I was 17 when I made this post. A couple of months shy of 18. Had never owned a 4-stroke before and found the valve train a bit like black magic at the time. 

 

I was buying this at the time: 

Cheap little Spanish made bike that had Yamaha mechanicals from an old off-road bike. There was a off the shelf high performance cam/cylinder kit that took them to something like 180cc that were dirt cheap. 

Most people told me to buy a bigger bike, and I couldn't even fathom the extra insurance costs, so was getting frustrated with that being touted as the main option. I gave up on the plan as I bought a car to do the getting around duties.

 

I moved to London that November, and bought a GPX400 for a few hundred quid. Didn't like it, so essentially traded it for a CBR125, which I did like and I spent many a night in the garage doing various services it didn't need, but I wanted to learn. And is why I have a little CBR125 project in my garage now.

I once got over 60 on a Honda 50 (down-hill wind behind). The engine seized just after that!