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CG 125 tuning

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Zygotic
L Plate Warrior



Joined: 24 May 2004
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PostPosted: 23:25 - 24 May 2004    Post subject: CG 125 tuning Reply with quote

i ride a 1989 CG125 (brazilian model) i`d like to know what i can do to make it faster i`m not really mechanically minded so its gotta be quite simply to do

at the moment i can get to 65mph at a push on a flat road with no wind

cleaned the air filter at the week end and seems to respond better

anything else i can do?
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craigT19
Jolly Green Giant



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PostPosted: 23:35 - 24 May 2004    Post subject: Reply with quote

errmmmm tow it Laughing


seriously tho...thats all your gunna get, the honda 124cc 4stroke dohc engine is pretty....ermm weak to say the least.

regards
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jimbo
Borekit Bruiser



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PostPosted: 11:55 - 25 May 2004    Post subject: Reply with quote

Heehee, the venerable cg125 Thumbs Up Like most bikes, someone, somewhere in the world, tunes and races them. I looked into them a while a ago. They are raced in the US and Japan, but have never been able to find off-the-shelf tuning parts for them.
Problem is, it's mostly machine-shop work to modify the engine bore, stroke, port size, cam profile. Nothing simple like you're looking for.
Basically the CG125 is designed to be a rock-solid commuter, and is very good at it's job. The trade-off is that it's pretty detuned and won't take much tuning.

Putting a larger front chain sprocket (1 or 2 teeth) or smaller rear sprocket (less 3 or 4 teeth) might give you a bit more top speed. It depends where the power is on the rev range.

There might be a K&N filter that would fit your airbox or could be trimmed to fit. Usually gives a better feel but not much more power. Carb jet might have to go up a size with this. A sock filter isn't an option as there is no protection from the elements on the CG.

Getting complicated:
There is a big brother of the cg125, the cg150, not sold in Europe as far as i know. I'm sure the barrel would bolt straight on to a 125 engine.

There are plenty of 4-stroke motocross 125s around, so an engine tuner who tunes these will probably be able to give you an idea what can be done. For example, there might be exhausts that can be altered to fit (at a price).

The cg125 can easily be adapted for nitrous oxide injection, though i saw this in a bike mag and the engine blew after a few miles. On the other hand, it was a clapped out banger of a bike. I'm sure it would be ok if installed properly on an newer engine.

A simple way for silly thrills is to run the engine on damp-start (comes in a can from any motor shop, mainly methanol and expensive). Saw this on a GS125, and it wheelied like crazy for a few miles until the head gasket blew. Not great for long term modification, as the methanol attacks some plastic parts (and little details like jetting and the lack of valve lubrication)

On the bright side, the CG125 puts out a stonking 11hp, which is equal to the new CBR125! So you can find a CBR to play with Very Happy
Some tuning parts may appear if the CBR gets established.

Hope this doesn't dissappoint too much. Let me know if you do find anything that can be done to the CG. I'm always interested Thumbs Up Karma
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badlydamaged
Spanner Monkey



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PostPosted: 12:06 - 25 May 2004    Post subject: Reply with quote

My friend has a brazillian CG 125 with a "racing exhaust" apparantly, we found it on an old CB125 field bike. I would guess its given him 2 hp more than he had, hes a big bloke (19 stone) with the aerodynamics of a 19 stone bloke in a waterproof coat that resembles a snowman suit whenever he goes above 40mph, and his CG will do about 70 - 75 mph on the flat now (suprised me with the difference considering its a 4 stroke), and I belive it had standard gearing. It may be worth trying it without that baffles, as its not too loud (quite quiet unless the throttle is wound right up, although it may be relitive to the shockingly loud exhuat less two strokes we have run in the past). Other than that like jimbo says, put a bigger diameter carb on, and try a performance airfilter. Hope you have some luck with it, and enjoy it!
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mr.z
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PostPosted: 15:34 - 26 May 2004    Post subject: Reply with quote

The only way you will get the cg to go any faster (legaly) is to loose some weight off it and yourself, even that won't make a tremendous difference, even if you did make it go any faster it would explode in a short time. apart from that trust me you don't want to go any faster than that, 73mph (indicated) on a cg125 is NOT something you'd want to make a habit of.

So - either go and buy an nsr 125 (which will cost you allot less than a cg wich will explode within 2/3 miles)
or just live with the snarling beast that you have, it will keep you going till you can move up to something biger, appreciate it for what it is... cheap, easy to live with and relyable, if you want expensive fast and not quite so easy to live with there are allot of 2stroke 125s out there waiting to scare the liveing **** out of new riders and old.

Trust me, been there done that, as many here have, the cost and difficulty not to mention explodeing engines is simply not worth considering.

Ride for half a year, book test, do test, pass test, buy new bike.
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Robby
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PostPosted: 18:23 - 26 May 2004    Post subject: Reply with quote

Tuning a CG is something i'd love to do.

First thing though - Craig, its not a DOHC single, its an OHV (pushrod) single.

Well it all depends if this is a project or your day to day ride, but here are the things I'd do if i had one to play with. Bear in mind the aim would be to get it to go as fast as... a rover metro.. until the engine blows.

In no particular order.

1. Get the head and base gaskets out. Make sure the surfaces are good and clean, and mate well. Use silicon sealant on reassembly. Or araldite. Should be a laugh.

2. See about getting some roller bearings into the bottom end. I'm sure some kind of size would fit, and cut down on friction a bit.

3. Skim the flywheel down a bit. Might help, or least make it vibrate more and feel faster.

4. Get a racier cam. Or attack the standard one with sandpaper, see what profile you end up with.

5. Bigger valves. Its such a simple head, I'm sure you could squeeze some bigger ones in. Clean up and polish the ports while the valves are out.

6. Colder plug, just go up by one number and see.

7. 8 inch long exhaust pipe. Point it at the road, no baffles.

8. Rip out the airbox. Run an open carb with a metal mesh over the mouth.

9. Bigger jet. Maybe bigger carb, but you may have to spend money here.


That should give you an engine gauranteed to fail quickly.

Shave some weight off the rest of the bike too. Ditch the indicators, battery, starter motor if it has one. Try a smaller headlight. Ditch the side panels - No need for them if you remove the airbox and battery. Cut the foam out of the back of the seat, remove the rear pillion footpegs and hangers.


That would be cool. Well it appeals to me.
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Kickstart
The Oracle



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PostPosted: 23:23 - 26 May 2004    Post subject: Reply with quote

Hi

65 isn't bad for a CG125. The engine is in a fairly low state of tune, and it would not be easy to get a serious amount of extra power out for it. For example the engine only has a single cam (no I don't mean cam shaft, I mean cam), with 2 rockers operating on different parts of the cam to open the inlet and exhaust valves. That greatly limits what you can do with the cam.

Probably the best thing to do would be to remove the air filter (which will dramatically shorten engine life), jet the engine to suit, play with the exhaust, increase the compression and maybe clean the ports up.

Or far easier would be to buy an XL185 engine and slot that in.

All the best

Keith
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cagiva gezzer
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PostPosted: 01:41 - 27 May 2004    Post subject: Reply with quote

If you're really serious about getting stupid power out of a cg, join the forum on www.macdizzy.com .

The forum is mainly 2 stroke, but there is some SERIOUS cg tuning going on. There areople on that who know which year head to put on due to it having better gas flow and petty things like that.

The 'boxes in various 4 stroke hondas are interchangable aswell

Its $10 to join (i think), but could be well worth it.
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jimbo
Borekit Bruiser



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PostPosted: 11:32 - 27 May 2004    Post subject: Reply with quote

Quote:
1. Get the head and base gaskets out.

Easy to do, but don't forget to adjust the valve clearances. It's a push-rod engine, not OHC.
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stevo as b4
World Chat Champion



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PostPosted: 00:24 - 31 May 2004    Post subject: Reply with quote

I agree with keith, that the XL185 motor should drop in easy enough, or even the XR200 engine (20bhp) thats nearly twice std! Erm for serious tuning, your better with the OHC 125/150 Honda engine as used in the CB and Xl/XR's. The ohc motor can rev higher without the worry of snapping/bending a push rod etc. For any real increase you need to go to 150cc or more as you wont get much extra power of the ohv 125 otherwise. The area you want to concentrate on is the head, it should be skimmed slightly and gasflowed. wouldnt bother fitting bigger valves or going to alot of trouble unless you have the OHC engine. its a simpler job then to swap the cam, and if you can get a CB125J cam or else an aftermarket performance XR125 cam, that would make a difference. to increase the Compression ratio on a 4 stroke like this you need a different piston with a bigger crown, and valve cut outs. Other than a head job, id use a sports silencer or a small megaphone (awesome sound) on the std downpipe, and fit a clamp on filter. The carb is only worth changing if you have a big valved modified OHC head with larger ports to suit. A Mikuni TM24 or VM26 would be a good carb to use then. The CG with the head done and some sort of sports exhaust set up may make another 2bhp, but thats another 5-6mph i would say on a light bike like the CG. The old CB125J similar to the CG, but with a tuned OHC engine made 13-14bhp and could do 75mph. If you went for a 150cc bored out OHC motor with tuning and bigger carb, i reckon you could see 16bhp, which in a CG chassis would be alot of fun. The XL185 has 18bhp, but i dont think id want much more, the CG's brakes are very weak, and the suspension would struggle too.
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Old Thread Alert!

There is a gap of 3 years, 88 days between these two posts...

cg_deano
L Plate Warrior



Joined: 27 Aug 2007
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PostPosted: 21:20 - 27 Aug 2007    Post subject: my cg Reply with quote

i have a brazilian cg125 n started customising it my self so far i got lower handle bars, bigger wheels, twin dom headlights, 400cc universal exsorst 200cc carb, and a k&n cone air filter. figuring out more things 2 do aswell!! i have found a 250 cc cg copy that is calld a lifan ghost buldog (pit bike) would slide and bolt with no mods 2 fram needed will let u no how i get on. oh yeah so far i had 90 mph down a very steep hill and 80 with a m8 on the back of me pmsl. any 1 have any questions just pm me
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Jamie S
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PostPosted: 21:30 - 27 Aug 2007    Post subject: Reply with quote

CG125 are not pushrod engines they are cam chain SOHC.
My old one was any way.
Confused
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Jamie S
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PostPosted: 21:39 - 27 Aug 2007    Post subject: Reply with quote

The only way to get a CG , CB, Tl, XR ,XL 125 ect (same engines just different gear boxes) is to fit a sammy miller 150 kit From here. http://www.sammymiller.co.uk/acatalog/TL125.html
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Jamie S
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PostPosted: 21:44 - 27 Aug 2007    Post subject: Reply with quote

Just realised how old this thread is !!! BAD NEWBIE cg_deano.
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Kickstart
The Oracle



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PostPosted: 21:52 - 27 Aug 2007    Post subject: Reply with quote

jamie stokes wrote:
CG125 are not pushrod engines they are cam chain SOHC.
My old one was any way.
Confused


CG is / was a pushrod engine. The OHC ones with a similar engine were the CB125S and the like.

All the best

Keith
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cg_deano
L Plate Warrior



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PostPosted: 17:42 - 28 Aug 2007    Post subject: cg125 Reply with quote

na u all wrong mine a 92 and they are pushrod till the 97 wich came out with the starter motor il send ya pics if ya dont belive me
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cg_deano
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PostPosted: 17:52 - 28 Aug 2007    Post subject: my cg Reply with quote

this is wat i done sofar
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.Chris.
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PostPosted: 18:02 - 28 Aug 2007    Post subject: Reply with quote

The new one is pushrod so I find it slightly unlikely that they'd have gone from a pushrod design to OHC and then back again.

From the CG125 page on the Honda Website (here):

Quote:
Engine Type - Air-cooled 4-stroke OHV single cylinder

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Maxx England
Derestricted Danger



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PostPosted: 15:50 - 31 Jan 2008    Post subject: Reply with quote

We're racing with FAB Racing this year (heirs to the Moped Mayhem series) with an Aprilia frame and CG motor. One point to change before all else is the carb. The standard one is leaner than an anorexic supermodel, a decent carb and jetting transforms the little soul. A cheap cam grind to the XR200 timings is going to be done. The ports are quite big anyway, so only clean up any roughness. Total header pipe length from the exhaust valve head needs to be about 28" (x 2.54 for cm). There will be higher compression pistons available, that will give a bit more shove as it's quite soft on compression as standard (to enable it to run on rum or paraffin etc in SE Asia).

The true CG is a pushrod motor, cleverly arranged so it's not far short of an ohc in terms of max revs possibe before valve float.

Have fun y'all.
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ms51ves3
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PostPosted: 16:53 - 31 Jan 2008    Post subject: Reply with quote

The original post was in 2004, I don't think he/she is here anymore.

Last edited by ms51ves3 on 16:06 - 26 Jan 2009; edited 1 time in total
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Maxx England
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PostPosted: 12:49 - 01 Feb 2008    Post subject: Reply with quote

It's OK, the info is just there for anyone else who wants a sleeper to upset kiddies who think they're fast (funny how we never see that sort on a track).

Moped Mayhem site gives links for a number of tuning places etc, also all are welcome to join us in cheap thrashing & crashing.
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Nigel_NS125F
Derestricted Danger



Joined: 31 Mar 2008
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PostPosted: 12:57 - 26 Jan 2009    Post subject: CG125 Reply with quote

quick question. i'm not particularly interested in making my cg faster, but i wouldn't mind being able to do cruise at 60mph without thrashin the hell out out it...as 60 is somewhere near 9000+rpm on my 4 speed cg...be nice if i could get it nearer 8000rpm.....would a smaller rear sprocket, say about 2 less teeth, work for this???
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lydanial
Brolly Dolly



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PostPosted: 15:57 - 26 Jan 2009    Post subject: Re: CG125 Reply with quote

Nigel_NS125F wrote:
quick question. i'm not particularly interested in making my cg faster, but i wouldn't mind being able to do cruise at 60mph without thrashin the hell out out it...as 60 is somewhere near 9000+rpm on my 4 speed cg...be nice if i could get it nearer 8000rpm.....would a smaller rear sprocket, say about 2 less teeth, work for this???


dont you have another gear?
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Kickstart
The Oracle



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PostPosted: 16:09 - 26 Jan 2009    Post subject: Reply with quote

Hi

It would need about 5 teeth less on the back (or equivalent) to bring the revs down from 9k to 8k (and good chance it wouldn't pull such high gearing).

All the best

Keith
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The last post was made 5 years, 85 days ago. Instead of replying here, would creating a new thread be more useful?
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