Modding a CG - A Young Fool acts Young and Foolish

[MattShill]

Following on from the 'derestricting an SR125' thread, I've been looking into the practice of 'jetting the carb up'. Now there's usually a fair amount of distain for any project involving the words 'improvement' and '125', but it's gonna be a while before I get it together to do my test, then get the cash together for a better bike, then get the cash together for insurance, so in the meantime I'm going to be riding a 'boring 125'. During that time I'd like it to be the least boring 'boring 125' it can be without resorting to screwing on bits of tat.

From what I've gathered you get a larger main jet and stick it in the carb. Will a larger one fit into the stock jet holder or would I have to replace the whole jet assembly? My manual says that my model has a '85' main jet (I think it reffers to mine, there are a few listed). 85 what? If this is indeed the value which wants increasing, what would be a good value to increase to? I'm assuming too big a jet would drown the engine and I can do that by leaving the choke on. Is it actually worth doing at all?

If that all goes well I'll have an engine running faster because it's getting more fuel. If it revs too highly the whole thing would be a waste, so would a larger front sprocket complement the new jet nicely?

These questions aren't really aimed at anyone, more of a description of the idea and the points which are confusing. I hardly know anything about all this as you can probably see, but there's the plan. Feel free to shoot it down, but give your reasons. Any advice would be great.

Matt.
____________________
Living life in the second overtaking lane!

'98 Kwak ER-5

[EuropeanNC30R...]

If you're putting more fuel in, your gonna need more air to go with it. Got an old snorkel handy for the airbox/filter?

Then you'll be needing to get rid of these extra gases quicker - time to drill the baffles out of your exhaust.

Of course all this will probably cause your bike to run like a pile of shit and use more fuel for the sake of sod all extra performance.

[ts50x0]

yep mate, just leave it alone. some idiot tried making my cg go faster before i bought it by taking the air filter out and putting in bigger jet!!!!!
yes it ran like apile of crap untill the revs got the pint where it was about to explode and it ran more like a 2 stroke with a powerband, and a weak one at that, as soon as i sorted the problems its is much more powerfull and starts and runs soooo much better.
your bike is suposed to be boring as you are alearner, think how i feels ive had my cg for about 2 months with a FULL lisence. just spend your time learning to ride, get through your test and get a bigger bike, i know how you feel but seriusly just leave well alone.

[ZaphodBeeble]

I agree with TS, don't bother doing anything to it. It really won't be worth your while. It's a lot of work for no real gain. On the other hand though, you might enjoy tinkering with it. It's obviously up to you but I wouldn't bother, I'd rather have it run smoothly and be reliable.
____________________
Current bike: VTR1000F Firestorm. Previous: Firestorm (written off) - XJ600 Divvy - NSR125 - DT125 and a load of offroaders.

[Wave2k]

find a fireblade engine off ebay and put that in it
____________________
Ducati 1299 Panigale
2009 Corvette C6 z51
RS125->CBR400->RXS100->GSXR750K2->Ducati749S->CBR600RR5->TL1000R->DRz400->RSVR1000->Honda VTR SP1->CBR400->GSXR1000K6->Honda H100->CBR600RR3->Ducati1299

[G]

Maybe look at getting some spare carbs/air box and an old exhaust to play with.

That way you don't bugger your bike up too much hopefully and still get a chance to 'play'; a cg125 seems to be ideal for such playing and learning about that sort of thing compared to the hassle of changing jets in a big multi.

[Kickstart]

Hi

For more performance you are not looking for more fuel to be burnt, you are looking for more air to go through and the right amount of fuel for the amount of air. Just sticking a larger main jet in will quite possibly loose you power.

Exhausts can help, but the silencer (the bit people change) is not really that important (although a bad design will loose you power. The length is important (and on multicyliner engines, the lengths until pipes from each cylinder join, and in what order they join). As a cooking analogy the silencer is the cherry on the top of the trifle, but it does no good at all if rotten fruit, lumpy custard and off cream was used.

One of the main things to improve an older or low performance 4 stroke would be to change the cam. Unfortunatly the CG uses a single cam for both the inlet and exhaust valve, just with 2 rockers mounted in different positions. Dirt cheap to make but a lousy idea for performance. Probably rather difficult to get any improvement at all, and very easy to loose power.

If you want more power from a CG I would suggest the first thing to do is to dump the standard engine and slot in one from the CB125S or older XL125. These were overhead cam engines and capable of producing rather more power (but also somewhat less reliable and requiring more frequent oil changes).

All the best

Keith
____________________
Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[mr.z]

Been there done that i'm affraid...

Theres NOTHING that can be done to the cg to make it go significantly faster without makeing explode in double quick time and looseing you allot of money in the meantime... it simply isn't sesigned for fast.

If you need to go faster then trade the cg in for a an nsr125, if its still not enough have someone help the restrictors fall out..

Theres aways the doing the test thing people tell you constantly, and i hate to tell ye but they are right

imo

spend money on das (and be a better rider too)
or a 2stroke sporty beast
____________________
>RidingSkills<->Tech Tips<->MyBikes<

[lilredmachine]

You would notice a difference if you managed to get an old cb125 twin motor in it. That might be an idea if I get a bit of spare cash...
____________________
Bikes: too many, too much for one man to maintain anyway.

[EuropeanNC30R...]

I found this story amusing a few years back when I was looking at 125's.

[Kickstart]

Hi

125 Superdream enigne will be barely any more powerful (and the extra weight would compensate for the extra power). The older pre Superdream twin would probably go in and would gain him about 50% more power, but the newest ones are over 20 years old, will have been thrashed to death, and it is hardly cheap when you need to change the carbs, exhausts, coils, etc as well.

XL185 engine might be fun .

All the best

Keith
____________________
Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[mrchips]

As the old saying goes, "if it ain't broke don't fix it"
____________________
Northern Irish? www.nibikers.com

[DM]

Entertaining read, Maurice .

But alas, these guys are right. If you had a 2-stroke then your tuning options would be significantly higher, but a cg wasn't made for it.

[bish777]

whack a spike down the zorst to make it free'r or fit a througher silencer, remove the airbox, slap a pod filter on the carb. move up a jet size and/or shim the needle a bit.

Not a huge power gain but some non the less.
____________________
GSXR1100J

[MattShill]

Right, thanks everyone! I didn't think it would be that viable but I needed something to occupy my mind during study leave. Good story, maurice, and it goes to show I should leave well alone!

Maybe once I've got something else it might be worth having a mess about with, but for the time being I'll keep it roadworthy.

Another edit: This new engine business sounds like a bit of a lark though. I was considering getting a standard CG engine+gearbox anyway because of the wierd configuration of mine, so if I can get a bit more power as the same time without ruining the bike it's probably worth a look. I'll keep an eye open.
____________________
Living life in the second overtaking lane!

'98 Kwak ER-5

[TheShaggyDA]

How much do you weigh? If you've got a few stone you can shed, it'll help the bike enormously.
____________________
Current: CB500 Previous: CB100N, CB250RS, XJ900F, GT550, GPZ750R/1000RX, AJS M16, R100RT, Enfield Bullet

[i:6e3bfc7581]But still I fear and still I dare not laugh at the madman...[/i:6e3bfc7581]

[Milo]

[J.K.R]

The First bike i had was an XL125(rf - disk front brake) Stainless Straight through exhaust Sounded the nuts, went like the clappers (bearing in mind it was the first bike i had driven!) Choke had to be cable tied down (full throttle made it run like poo with the vibration)

Anyway, leave it as it is, clean it, polish it, cherish it, dont modify it (Unless needs be) Sell it buy bigger bike, tastefully modify it, clean it, polish it, cherish it, (keeps going on from here)

hth
____________________
www.oldskoolsuzuki.info

[stevo as b4]

The problem with a CG is that the brakes are pretty crap, and so more power would not be advised or safe really. Even 15bhp would be too much for the brakes to cope with.
As for engine swaps, well, like Keith said, the CB125T is a waste of time, although i like the CB125 twins themselves, especially when tuned to the same 16bhp as the older CB125 twins were.
The CB125J engine which is basically an OHC version of the CG is likely to fit, but its probably a bit taller, and with the hassle of moving/welding engine mounts, its still only 12-13bhp.
The XL185 would be interesting in a CG, but these engines wern't that robust, and are quite rare now i would think.

[mchaggis]

Modifying your CG engine? Mine siezed today. Good luck.
____________________
I must not be a troll...
Mmmm, Guinness
Discovering the delights of Hammerite and a 3/4" brush.

[EuropeanNC30R...]

[Minithugg]

[Darth]

Seriously? 5 year old thread revival? That has to be near a record?? Did enjoy reading the post about the guy who tried modding the cg engine though
____________________
Harold_Shand wrote: I suppose it's like anything, you get your fingers burned when you start out, you learn from it and eventually become a complete arsehole about the whole thing.

[MarJay]

[Kickstart]