Old CG125 a little sluggish

[la_lucha]

So I've recently acquired an old CG125 and it underperforms a bit in my opinion. What would you guys do to ensure that it runs at its optimum, bearing in mind that it is quite an old bike.
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Feck Orf

[MarkJ]

Set valve clearances, new air filter if it needs one, check fuel mixture is correct, new spark plug, maybe oil change if needed.

[Rogerborg]

Check the plug colour, condition and gap. Re-gap or replace as required. Oil change. Clean the float bowl and jets, do some plug chops and change the needle position and/or jets accordingly. Fit a fuel filter. Check the strength of the spark, and the condition of the wiring on the ignition circuit and engine earth. Check the valve clearances. Check the ignition timing.

After you've done all that, you'd have been better off buying a newer bike.

hondacg125.awardspace.com is a handy resource.
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Biking is 1/20th as dangerous as horse riding.
GONE: HN125-8, LF-250B, GPz 305, GPZ 500S, Burgman 400 // RIDING: F650GS (800 twin), Royal Enfield Bullet Electra 500 AVL, Ninja 250R because racebike

[la_lucha]

Cheers boys. I had better find me a copy of the old haynes to make sure I do all that stuff right.
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Feck Orf

[hazza]

https://www.mediafire.com/?6824i9hx6zzdmd2

there you go.
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3 Honda NC50's(Sold)-->'72 Puch Maxi S (Sold, want it back!)--> '90 Yamaha RXS 100 (Stolen)--> '87 Honda Cub 90(Sold) --> '95 Kawasaki Eliminator (Sold) --> '98 Bandit 600 (Sold) -->'07 SV650S (Current)

[la_lucha]

I can't get on that site due to work restrictions. What's on there?
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Feck Orf

[hazza]

Its a link to download a haynes manual for the bike, save you buying a paper copy.
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3 Honda NC50's(Sold)-->'72 Puch Maxi S (Sold, want it back!)--> '90 Yamaha RXS 100 (Stolen)--> '87 Honda Cub 90(Sold) --> '95 Kawasaki Eliminator (Sold) --> '98 Bandit 600 (Sold) -->'07 SV650S (Current)

[Walloper]

They DO under-perform...
It is a One Hundred and Twenty Five cubic centimetre engine (Spelling it out makes it seem bigger than it is.)

You should be able to just about touch 68MPH (when tucked in behind the Speedo, on a level straight, 0-5mph headwind). Confirmed by writer using GPS.
It will seem slower to accelerate than most cars but with practiced conservation of energy techniques you can fly through town using inertia and forward planning, full use of available throttle, economic use of the brakes and the power of prayer.

https://hondacg125.awardspace.com/

They are brill for town though.
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W-ireless A-rtificial L-ifeform L-imited to O-bservation P-eacekeeping and E-fficient R-epair

[la_lucha]

[Shinigami]

i'd say there's a problem if it can't hit 50..

when you say it can't reach 50 over what distance is this?

My city fly can hit 50 reasonably easily and I'm lead to believe they're more sluggish than cgs..

[la_lucha]

[tomh]

How level is the road and how windy is it? Realistically if the road is going up hill the top speed is about 50mph or even less. If the road is flat or downhill you should be able to get 70mph top speed. The wind also has a big effect. A headwind will really slow you down and on one stretch of road I go on its always windy on a up hill part and I struggle to keep 35-40mph.

Also what sort of speed are you changing gears at? 5th gear is more like a overdrive gear so you need to get your speed upto at least 50mph for 5th gear to get you upto 70mph on a flat road.

I wouldn't bother changing sprocket sizes as there is a big trade off between acceleration and speed on a little 125cc. You can change the sprocket size for greater speed but then you loose the acceleration to actually get to speed.

If on a flat road with no wind and it still struggles to get you to more than 50mph then there is something wrong and I would suggestion checking compression, spark plug colour and clean the carb etc.

What year is the bike and many miles on the clock does it have?

However if it does get past 50mph you just need to get used to slow speed and learn the best use of the gearing ratio and more effiecent use of your brakes.

[la_lucha]

It'll do 55mph flat out on a flat straight with no wind. It's a 1979 with 20,000 miles. When knocking it up to 5th you can just tell it's not running at full tilt, but it can't be arsed to give anymore either.

With regards acceleration, I don't mind losing a bit as most of my journey is long straight roads so acceleration is not the key factor.
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[janner_10]

Doesn't sound a million miles from where it should be for a 33 year old CG
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Yamaha FZS600 (Now gone to heaven) > CBR600F4i (SOLD) > '99 YZF-R1

[la_lucha]

Yeah but what can I do to make it run better? I know these bikes are pretty simple, so what could be the main contributer to loss of power?

Just because it's old doesn't mean it should underperform.
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[Robby]

Fix the problems you know about before trying to find new ones.

So, if the front sprocket is too small, fit one the right size.

Service it. A dirty air filter makes a big difference, and they don't even need to be all that dirty. Washable foam filters in particular, I have thought they look ok until I soaked them in petrol. So much crap and grit gets caught up in the foam. Remember to re-oil with engine oil before refitting.

Make sure the brakes aren't dragging or binding. Quite common on drums brakes that haven't been serviced, or disc brake calipers that have sat and started binding due to corrosion building up behind the seals.

After servicing, take it out for a very hard ride to clean out all the crap and get it really hot. An Italian tune-up still works wonders on most vehicles.

Tyre pressures too.

In short, get the haynes, give it a really comprehensive service, check that the sprocket sizes are correct, then see how it performs.

[la_lucha]

Cheers Robby. I've ordered a chain and sprocket set and an Air Filter, so will hopefully have them on at the weekend. I'm also going to give it an oil change.

I've put a new spark plug on, so hopefully it'll all come together to give it a bit more oomph.
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[Hobgoblin]

[numpty2]

I had a CG125 for many years and I loved it, but I never managed more than 60mph with the wind behind me. I bottled out at this point because of the drum brakes. A lot depends on your size & weight - I was the equivalent of Jeff Capes riding a Shetland pony. They are really slow, but wonderful. Have pity on the old girl and just enjoy how cheap they are to run. I'd still have one now, but my commute is too far. An old bloke called Simon Gandolfi rode one from Mexico to the bottom of South America and then back again - 46000 miles I think. I sold mine as a runner with 44000 miles on the clock.

Another good source of info is: https://hondacg125.awardspace.com/
You might find something useful here. There are different spark plugs discussed, and the author reckons a windscreen can make a big difference.

If you want something a bit quicker, but just as basic, you could go for a Yamaha YBR125. These are just as easy to work on, lots of spares, and they are quite cheap for the carb models. On balance, I'd probably go for the YBR now over the CG125. Just for little things like better headlight, tubeless tyres etc.

[Walloper]

[la_lucha]

So last night I changed the spark plug, chainged the old strectched chain and changed the air filter. This morning the bike is far smoother and I have 10-15mph top speed gains.

Not bad for 15quid.
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[Walloper]

[Sako]

[Walloper]

[amaro12]