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Discussion Starter · #1 · (Edited)
I have a cg 125cc 10 thousand km driven was bought new kept fully stock. This bike is still in production in Pakistan and one the top selling hot cake despite an 80s-90s design.

Today i cleaned its filter and carb but it keeps running if i fully closes the mixture screw. That is very strange because on stock setting it should be 2 turns out.

If i 2 turs out than it will not ideal perfect and lowers the rpm and dies like if it gets too much rich. It ideals fine at fully closed or half turn out. more than half turn out and i can tell by sound that its getting much richer inside. ?

(A bike on ideal sound heavier like boog ... boog ...boog if its too rich.
on leaner or correct mix it is like bag.bag.bag lighter tone and closer bangs.
just for info.
)

Chock is also working fine. Carb is pz26

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Did you put the round slide back in the correct way? or is it rotated 180 degrees from where it should be
 

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Then I would clean it again, if one screw adjustment on a carburetor does nothing, that implies that fuel or air circuit is plugged.
 

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Today i cleaned its filter and carb but it keeps running if i fully closes the mixture screw. That is very strange because on stock setting it should be 2 turns out.

If i 2 turs out than it will not ideal perfect and lowers the rpm. It ideals fine at fully closed or half tur out ?
By saying the mixture screw are we talking about the screw at the front, center and is low on the underside of the carburetor with the head of the screw about half way up from the bottom of the fuel bowl... Yes? I ask because the screw that is prominent in the pic is the idle speed / slide stop screw on the side of the carburetor.
So, the fuel mixture screw...
I've had some of the smaller, older well used bikes run best (not ideal) when the fuel screw was turned all the way in, or nearly all the way in to it's seat. The (a) theory as to why it ran better with the fuel screw turned in was that a small amount of oil was getting past the rings actually making the mixture richer from oil. Those bikes had an old, weakened ignition system that might have had something to do with the condition, maybe?

If you put a fresh spark plug in it and run it for a while what does that plug come out looking like?.
Does the engine have fresh oil in it?

S F
 

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If the idle SPEED screw shown on side of carb in pic 3 is in too far the slide itself will be high and expose transfer holes to feed fuel even with idel mixture 100% shut. Unscrew that screw on carb side counterclockwise and it will begin to drop idle way down. The idle mixture screw may be the one just barely showing on FRONT of float bowl NOT the bottom which is a simple drain screw.
 

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Just to avoid confusion:
** I'm thinking you probably meant to say idle speed mixture screw.
:)

S F
 

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Would this picture with them numbered help identify which one is actually being changed?
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That's provided I actually got them all to begin with.:whistle:
 

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Discussion Starter · #9 · (Edited)
Sorry for confusion that's the mixture screw. precisely petrol regulator (not air regulator).
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Other thing is that this carb and bike has ASV System.

My post caused some confusion and looks like that i got this problem yesterday after reassembling the carb but in fact it was running like this on just half turn out. Last time by byke was serviced by Honda Center and i regret i dont know what the fk they do with my byke.
 

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Discussion Starter · #10 · (Edited)
By saying the mixture screw are we talking about the screw at the front, center and is low on the underside of the carburetor with the head of the screw about half way up from the bottom of the fuel bowl... Yes? I ask because the screw that is prominent in the pic is the idle speed / slide stop screw on the side of the carburetor.
So, the fuel mixture screw...
I've had some of the smaller, older well used bikes run best (not ideal) when the fuel screw was turned all the way in, or nearly all the way in to it's seat. The (a) theory as to why it ran better with the fuel screw turned in was that a small amount of oil was getting past the rings actually making the mixture richer from oil. Those bikes had an old, weakened ignition system that might have had something to do with the condition, maybe?

If you put a fresh spark plug in it and run it for a while what does that plug come out looking like?.
Does the engine have fresh oil in it?

S F
yes that screw at front bottom. Nup i dont think oil has do do something here. Fully closing mixture screw means no fuel and oil and air dont produce bang.
A fully closed fuel supply screw and still running engine means its sucking fuel from some other place in carb :)

Yes oil is new in it. The plug color is crisp tan good.

Does those of your bykes had ASV on them and carb. some small diaphragm in carb ?
 

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Discussion Starter · #11 · (Edited)
If the idle SPEED screw shown on side of carb in pic 3 is in too far the slide itself will be high and expose transfer holes to feed fuel even with idel mixture 100% shut. Unscrew that screw on carb side counterclockwise and it will begin to drop idle way down. The idle speed screw may be the one just barely showing on FRONT of float bowl NOT the bottom which is a simple drain screw.
You seems right but ideal screw is not turned in too much it is just barely lifting the slide. it is correct. I tested that.
 

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Discussion Starter · #13 ·
hy guys, im thinking may be asv diaphragm in carb has to do something with it. bec yesterday i saw it and it was worn like a small needle hole in it. Dont know why only at 10 K it is worn out.

I ignored that and now im thinking that fuel is being feed from that tiny hole. I have to inspect it again. The problem is we dont have here carb rebuilt kits. thats why i have to fkin delete the asv system from my bikes. did the same with my other byke
 

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"The problem is we dont have here carb rebuilt kits. thats why i have to fkin delete the asv system from my bikes."
You saying you can't buy a carburetor rebuild kit therefore you need to delete the pollution control measures? That makes no sense and there should be no part of your carburetor worn out at this point.
 

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Thank you post #7 for the correction and I fixed it.

OP show pics of that valve, The other one on other bike you showed only switches AIR, there is no fuel there at all. Trace passages and you will find that out. When you get raw fuel up into an aircut valve it is sign of flooding carb, the fuel got too high. Normal is bone dry at all times.

With that location mixture screw you are adding fuel AND air, not just fuel. Again, trace the passages.
 

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If the mixture screw seat is damaged then it can still leak fuel at screw completely shut. Common with the fine holes Honda uses there and very easy to damage.
 

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Hi there ! .

I occasionally get ATLAS HONDA parts for my 1984 CB125S from Pakistan, are there no Honda dealer there ? .

I'm not familiar with the ASV system but any time you find a crack or hole in a diaphragm it's bad .

PZ26 kits should be available on line, what's the year or production of your bike ? .

Trails : THANK YOU for that PZ service file ! .

I have the PZ27, pictured but not mentioned in the booklet .

Is there perhaps a link to a Pakistani Honda parts place ? .

TIA,
 
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yes that screw at front bottom. Nup i dont think oil has do do something here. Fully closing mixture screw means no fuel and oil and air dont produce bang.
A fully closed fuel supply screw and still running engine means its sucking fuel from some other place in carb :)
Yes oil is new in it. The plug color is crisp tan good.
Does those of your bykes had ASV on them and carb. some small diaphragm in carb ?
OHHH! This is the bike that has plastic and stuff stuffed into the place where there used to be an air cut off valve.
Would have been good to lead off with that little tidbit of information... Just sayin

"
Fully closing mixture screw means no fuel and oil and air dont produce bang.
A fully closed fuel supply screw and still running engine means its sucking fuel from some other place in carb "
Quote - UserXXX

Yes sucking fuel from someplace like the needle jet. (Yep, even at idle). Or maybe from the "rigged" air cut valve stuffing job too?
A leakdown and compression test will give a clue as to the possibility of oil contributing to a richer idle speed mixture but most likely your carburetor just needs to be fixed.

What is an ASV?
What year model bike are we talking about?

S F
 

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There may well be a transfer hole as well at right where the front of slide would touch down at fully closed. Some have them and some don't. If mixture needle screwed shut then fuel pulls from there if slide is high enough and again the needle can dribble a bit to feed fuel too like said. Why I told somebody to completely drop the slide to dead shut, but one has to do it to get any idea of it.
 
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