2005 honda cg125cc with big bore 150cc upgrade, carb advice?

[SKWID]

Hi all,
first time posting on here and hopefully someone can help me out with my bike.

I recently stripped my bike down completely and converted my 125cc engine to a 150cc, I'm having some issues due to this being my first project too.

I believe I need to upgrade my carb and iv not been able to find something because I'm unsure what id need exactly.

The bike is a honda cg125cc 2005

any help would be appreciated

[stinkwheel]

If you haven't ported the head, there's probably not much point fitting a bigger carb. I'd expect you might need to tweak the jetting on the standard carb.

Depends how it's running. How is it running?

Tuning bikes is a can of worms, it's never plug and play. Even if it's sold to you as if it is. Take this from someone who just had to take a rotary burr to part of his crankcases yesterday to increase tappet clearance.
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[WD Forte]

so you've gone from 125 to 150cc
on a stock cg125 that's about 11 to 13 bhp
so nothing that's going to tear up the street.

But as stinkwheel says it's more complex
Just sticking a bigger jet or carb may not automatically boost performance and if you don't get it right it may be worse.

IIRC the ignition timing is fixed on those bikes so you can't alter that
Same head/exhaust? that can have an effect if its not porting the gasses well
valve timing comes to mind as well
CG's were designed to be reliable plodders not racers

What do you weigh?
if you're say 8 stone it may have a noticeable effect
if you is a fat bastard you may not notice much improvement.
Power to weight ratio and all that.

I once put an Xl500 lump in an RS250 and that was a larf
back to the CG in question, if I wanted moar powah and couldn't reasonably expect to at least double its existing 11bhp I wouldn't waste my time faffing about with it

Stick a 250 lump in
____________________
bikers smell of wee

[stinkwheel]

In fairness, there is a fair chance it won't need any changes to the carb at all.

As above, you haven't altered the stroke, porting or the valve and ignition timing, just the bore. Not sure how it would play regarding compression ratio, that would depend on the new barrel and piston profile.

In any case. Going from 125 to 150cc with a simple overbore, I would expect the bike to start and run well enough on the standard jetting to act as a basis for improvement, especially at low revs. If it's not running, I doubt fueling is the problem.

If Virus sees this, I think he had a 150cc CG125 at one point so may be able to give you some pointers. I very much doubt he bought a new carb for it, he was spending most of his money on beer at that stage.
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.