26mm carb on 125 problem - Honda Rebel Forum
 
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post #1 of 7 Old 11-10-2019, 09:24 PM Thread Starter
 
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26mm carb on 125 problem

Hi

I fitted a 26mm cg type carb to my rebel 125, which works fine(brown plugs) apart from one problem. At about 50 in 4th( no 5th gear, different problem) if i try to open the throttle more to go faster, it slows down or bogs a bit, so will not run with full throttle. What is the problem? needs bigger jets? or what else?

Thanks

Tigger

I love bikes, games, and women, not in any particular order.

1998 honda ca 125S rebel
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post #2 of 7 Old 11-13-2019, 09:38 AM
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I would say...... (your milage may vary)

As long as you are keeping the float bowl filled. Good fuel, flow and filter. I would say buy some jets.
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post #3 of 7 Old 11-13-2019, 07:17 PM
 
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What's the jetting like? Mine is running the original carb with stock settings now (95 main jet, 38 pilot, needle shim on the 3rd slot, air screw at 1 3/4 turns out) and goes up to 60mph without issues.
It's maybe too rich on full throttle if your plugs are brown, my stock settings are quite lean but the bike pulls fine. Took me a while to get there but my carb is sound now.
Check the needle and see where your shim is at and maybe have a play around with that first, probably the increased air flow of the cg carb is messing up the mixture. Other than that the CA125 is awful at getting past 50 even with 5th gear and i think that's just the engine.
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post #4 of 7 Old 11-13-2019, 07:24 PM
 
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Triggerlator - I have an AFR gauge on my 250. You might read the AFR thread, good info. If you are running the stock settings for a 250 on that carb, then it sounds to me like your engine is getting way rich at 50 mph.

If you look at the Rebel AFR thread you'll see a graph of the AFR across a wide range of rpm, but based on speed. In the graph, the AFR is just cruising ... at each speed. The graph makes it clear that at 50 mph the main jet begins to really contribute.

Your situation will differ somewhat based on your smaller displacement. My main point I guess is ... the stock carb can REALLY DELIVER the fuel. That graph also shows WOT AFR, and the AFR at WOT is VERY rich. The 250 engine gulps it down well though. But my guess is your engine is simply getting too much fuel.

2 sizes smaller main jet would be a good place to move to and see if it is better.


7milesout

2016 Honda Rebel 250 - The "Piglet."
AFR sensor equipped and downsized to a 0.105" main jet.
The only changes so far.
Bought on 6/29/19 with 44 miles.
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post #5 of 7 Old 11-14-2019, 04:19 PM
 
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Quote:
Originally Posted by 7milesout View Post
Triggerlator - I have an AFR gauge on my 250. You might read the AFR thread, good info. If you are running the stock settings for a 250 on that carb, then it sounds to me like your engine is getting way rich at 50 mph.

If you look at the Rebel AFR thread you'll see a graph of the AFR across a wide range of rpm, but based on speed. In the graph, the AFR is just cruising ... at each speed. The graph makes it clear that at 50 mph the main jet begins to really contribute.

Your situation will differ somewhat based on your smaller displacement. My main point I guess is ... the stock carb can REALLY DELIVER the fuel. That graph also shows WOT AFR, and the AFR at WOT is VERY rich. The 250 engine gulps it down well though. But my guess is your engine is simply getting too much fuel.

2 sizes smaller main jet would be a good place to move to and see if it is better.


7milesout
The 125 carb is a completely different design to the US 250 model, it's a much cheaper variation. The CG type carburetor is a 125cc also, it's a Mikuni but it is very similar to the CA125 (Rebel) carburetor, it just has a larger venturi.

This is the stock one here for the 125 rebels in the UK, it's a Keihin.
https://www.fowlersparts.co.uk/parts...mkh/carburetor

The advice for the Rebel 250 is therefore not much use to anybody on a 125. I would just advise to use the stock Keihin carburetor with stock settings, it runs beautifully like that.
There is an englishman on youtube advising everybody to get chinese knockoff CG125 carburetors but to be honest the stock carb does the job fine, I can do 60mph which is unheard of for a Rebel 125 hahaha.
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post #6 of 7 Old 11-15-2019, 12:20 PM
 
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I must have misunderstood. I thought the O.P. was saying he put a 250 carb on a 125. If not, just ignore my post.

2016 Honda Rebel 250 - The "Piglet."
AFR sensor equipped and downsized to a 0.105" main jet.
The only changes so far.
Bought on 6/29/19 with 44 miles.
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post #7 of 7 Old 11-18-2019, 12:15 PM
 
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Quote:
Originally Posted by 7milesout View Post
I must have misunderstood. I thought the O.P. was saying he put a 250 carb on a 125. If not, just ignore my post.
Nah.. the CG is a 125cc bike which was the equivalent of your Rebel 250 in the USA, the universal learner bike. The CG's carb won't work well without being re-jetted on a rebel anyway because it's a different bike and different set up, the CG has quite a bit more power and i'd assume more fuel flow.

I have noticed that the Rebel 125 has a bog but i believe it's caused by the throttle needle being set too high from stock (middle shim), you can rev the bike no problems with the choke in but choke out and it seems to cut out when you're at idle or bog when you're on the move. Suggests to me that the bike runs a little rich at 3/4 throttle, could do with the shim raised / needle dropped but i'll see how i get on with that when I get round to it
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