Possible intake leak - Honda CBR 125 2004

[MR_W]

My sister's 2004 CBR 125R did havoc in a similar way on idle with a buggered throttle cable. I believe it was replaced and re-routed a bit.

[jamessk98]

Yeah but a leak could still cause the idle to fluctuate? The two issues might be unrelated, which is why I suggest it may be sticking open once it’s been opened up.

 

I should have mentioned but it has been sat for a few months.

However it spits flames so surely an air leak will cause it to run lean right?

The problem wasnt there before christmas, but is now and i havent even touched the carb

 

It will spit flames if its running RICH, it's the un burnt fuel that's igniting.

 

Yeah I know, hence the diaphragm being broken and stuck open, pouring LOADS of fuel in.

[jamessk98]

My sister's 2004 CBR 125R did havoc in a similar way on idle with a buggered throttle cable. I believe it was replaced and re-routed a bit.

 

I was thinking possibly, but the then it returns fine and is smooth. The idle was smooth at the start of the day and the throttle hadn't been touched or barely even moved

[Via]

Really don't think fuel would cause this... you'd more likely find it bogging down on acceleration and having difficulty starting (dumping too much fuel in while sitting there and then hydro locking).

Air is what makes an engine go, hence turbos & superchargers are all about getting more air in quicker.

If air leak is ruled out and you're positive cable is not jamming then I'd look at carb, is throttle body closing correctly?

[Tango]

If it's been stood for a while try some fresh fuel.....but drain the tank first....

[jamessk98]

Really don't think fuel would cause this... you'd more likely find it bogging down on acceleration and having difficulty starting (dumping too much fuel in while sitting there and then hydro locking).

Air is what makes an engine go, hence turbos & superchargers are all about getting more air in quicker.

If air leak is ruled out and you're positive cable is not jamming then I'd look at carb, is throttle body closing correctly?

 

yes the throttle is closing properly, and i know for a fact the diaphragm is broken as all of a sudden petrol pisses out of the tap unlike how a tiny bit would dribble out and that would be all.

i assume its dumping loads of fuel but not too much to stop the running of the engine and enough to just have a high idle. It stopped running well all of a sudden after the lines had been put on the wrong pipes. I went to a garage and explained it to them and they agreed it would be the tap diaphragm.

I do also know how an engine works btw.

[jamessk98]

If it's been stood for a while try some fresh fuel.....but drain the tank first....

 

well the tank was empty till the other day, i put in 5L of fresh fuel on monday. there was maybe 150ml left in the tank over christmas and whatever was left in the carb too.

[fastbob]

I should have mentioned but it has been sat for a few months.

However it spits flames so surely an air leak will cause it to run lean right?

The problem wasnt there before christmas, but is now and i havent even touched the carb

 

It will spit flames if its running RICH, it's the un burnt fuel that's igniting.

 

Yeah I know, hence the diaphragm being broken and stuck open, pouring LOADS of fuel in.

 

NO . There is a fuel metering device in the carb ( assuming this bike even has a carb and its not fuel injection ) consisting of a float and needle valve . A diaphragm in a fuel tap is operated by a vacuum from the carb intake . If a fuel tap diaphragm is damaged i.e it has a hole in it then it will not operate and you will get NO fuel. I'll tell you what , may i respectfully suggest that you get a Haynes manual called Motorcycle Basics and have a good read on what things are called, what they do and how they work . Once you understand the basic principles of things it will be easier to see what's wrong and put it right. I'm going to look at a parts list for this bike to see if it even has a petrol tap because there isn't one in your picture. There must be reserve function on this bike so it has to have a petrol tap .

.

[jamessk98]

It will spit flames if its running RICH, it's the un burnt fuel that's igniting.

 

Yeah I know, hence the diaphragm being broken and stuck open, pouring LOADS of fuel in.

 

NO . There is a fuel metering device in the carb ( assuming this bike even has a carb and its not fuel injection ) consisting of a float and needle valve . A diaphragm in a fuel tap is operated by a vacuum from the carb intake . If a fuel tap diaphragm is damaged i.e it has a hole in it then it will not operate and you will get NO fuel. I'll tell you what , may i respectfully suggest that you get a Haynes manual called Motorcycle Basics and have a good read on what things are called, what they do and how they work . Once you understand the basic principles of things it will be easier to see what's wrong and put it right. I'm going to look at a parts list for this bike to see if it even has a petrol tap because there isn't one in your picture. There must be reserve function on this bike so it has to have a petrol tap .

.

 

Then why would 2 people from the motorcycle garage both have said it?

I'm quoting from what they said, which was that one of the pipes go directly to the cylinder.

And if its broken and no fuel should be coming out, why is it pissing out more than ever?

[jamessk98]

It will spit flames if its running RICH, it's the un burnt fuel that's igniting.

 

Yeah I know, hence the diaphragm being broken and stuck open, pouring LOADS of fuel in.

 

NO . There is a fuel metering device in the carb ( assuming this bike even has a carb and its not fuel injection ) consisting of a float and needle valve . A diaphragm in a fuel tap is operated by a vacuum from the carb intake . If a fuel tap diaphragm is damaged i.e it has a hole in it then it will not operate and you will get NO fuel. I'll tell you what , may i respectfully suggest that you get a Haynes manual called Motorcycle Basics and have a good read on what things are called, what they do and how they work . Once you understand the basic principles of things it will be easier to see what's wrong and put it right. I'm going to look at a parts list for this bike to see if it even has a petrol tap because there isn't one in your picture. There must be reserve function on this bike so it has to have a petrol tap .

.

 

And of course i know its not EFI, and it has no reserve tank.

As you say the diaphragm is vacuum operated, it if it broken then the fuel will go through the carb and also what was the vacuum pipe, meaning more fuel will go in.

Edited January 17, 2018 by jamessk98

[jamessk98]

Yeah I know, hence the diaphragm being broken and stuck open, pouring LOADS of fuel in.

 

NO . There is a fuel metering device in the carb ( assuming this bike even has a carb and its not fuel injection ) consisting of a float and needle valve . A diaphragm in a fuel tap is operated by a vacuum from the carb intake . If a fuel tap diaphragm is damaged i.e it has a hole in it then it will not operate and you will get NO fuel. I'll tell you what , may i respectfully suggest that you get a Haynes manual called Motorcycle Basics and have a good read on what things are called, what they do and how they work . Once you understand the basic principles of things it will be easier to see what's wrong and put it right. I'm going to look at a parts list for this bike to see if it even has a petrol tap because there isn't one in your picture. There must be reserve function on this bike so it has to have a petrol tap .

.

 

Then why would 2 people from the motorcycle garage both have said it?

I'm quoting from what they said, which was that one of the pipes go directly towards the cylinder.

And if its broken and no fuel should be coming out, why is it pissing out more than ever?

[Tango]

Fastbob is right.....If the fuel tap diaphragm was split, then you'd get no fuel to the carb.......maybe the diaphragm the garage was talking about is the CV diaphragm in the carb......no 13 in the diagram.

[jamessk98]

Fastbob is right.....If the fuel tap diaphragm was split, then you'd get no fuel to the carb.......maybe the diaphragm the garage was talking about is the CV diaphragm in the carb......no 13 in the diagram.

honda-cbr125r-2004-4-england-carburetor_bigecpp4e1e__1800_f455.gif

 

But if it is operated by vacuum then surely when its not connected no fuel would come out?

When I take the tank off, fuel pisses out of the top line of diaphragm with no vacuum

[fastbob]

Right then , I've had a look and you are quite right, there is no fuel tap in the normal sense and again you are quite correct in saying that there is no reserve selector either. There is what is described as an Autocock which is the thing you have outlined in red . This device, based on its shape almost certainly contains a diaphragm that switches the fuel on when it is activated by a vacuum from the carburetor. From what I have seen so far, I don't think this thing can be opened up to replace the diaphragm. It seems that it must be replaced as a unit . So , provided you didn't pay too much for the tank and it's got the autocock still in it , that's that sorted then . However, even if this thing is stuck wide open, as I said the carb sill has a float and needle valve that controls the fuel flow into the carburetor float bowl. While I was looking, I was surprised to find that there does not appear to be a choke on the carb , instead there is a Starter Valve so that might be stuck ( see pics ) So anyway what I am basically saying is that a faulty autocock on its own will not cause over revving and spitting flames on it's own . http://i.imgur.com/S8esdqd.png see parts 15 & 7 maybe this thing is stuck . Also as previously mentioned by Tango, have a very good look at part 13 , this is the main diaphragm, check it for holes .http://i.imgur.com/gL3SwDJ.png

Edited January 17, 2018 by fastbob

[fastbob]

Oops , the 7 isn't in the picture, its all the bits above part 15 .

[fastbob]

Fastbob is right.....If the fuel tap diaphragm was split, then you'd get no fuel to the carb.......maybe the diaphragm the garage was talking about is the CV diaphragm in the carb......no 13 in the diagram.

honda-cbr125r-2004-4-england-carburetor_bigecpp4e1e__1800_f455.gif

 

But if it is operated by vacuum then surely when its not connected no fuel would come out?

When I take the tank off, fuel pisses out of the top line of diaphragm with no vacuum

Fuel shouldn't piss out that's true but I still don't see how this alone is causing the running problems .

[fastbob]

Does this look familiar ? http://i.imgur.com/nAILfp0.png maybe you are not alone .

[jamessk98]

Right then , I've had a look and you are quite right, there is no fuel tap in the normal sense and again you are quite correct in saying that there is no reserve selector either. There is what is described as an Autocock which is the thing you have outlined in red . This device, based on its shape almost certainly contains a diaphragm that switches the fuel on when it is activated by a vacuum from the carburetor. From what I have seen so far, I don't think this thing can be opened up to replace the diaphragm. It seems that it must be replaced as a unit . So , provided you didn't pay too much for the tank and it's got the autocock still in it , that's that sorted then . However, even if this thing is stuck wide open, as I said the carb sill has a float and needle valve that controls the fuel flow into the carburetor float bowl. While I was looking, I was surprised to find that there does not appear to be a choke on the carb , instead there is a Starter Valve so that might be stuck ( see pics ) So anyway what I am basically saying is that a faulty autocock on its own will not cause over revving and spitting flames on it's own . http://i.imgur.com/S8esdqd.png see parts 15 & 7 maybe this thing is stuck . Also as previously mentioned by Tango, have a very good look at part 13 , this is the main diaphragm, check it for holes .http://i.imgur.com/gL3SwDJ.png

 

Yeah I only paid £30 for the tank with a new fuel level sensor (my current one is broken too) and the diaphragm valve moboby thing. So not too bad, especially considering a whole new assembly is £60-70.

I plan to replace it and go from there, as the choke moves freely as it always has done and that wasn't touched before the problem occurred. That is why I believe it is the problem and nothing else, but I'll replace it and see.

I'll just have to wait till I'm back from uni and what is what.

[jamessk98]

Does this look familiar ? http://i.imgur.com/nAILfp0.png maybe you are not alone .

 

I will have a read now about this, but my idle is pretty shocking from the start

[jamessk98]

Does this look familiar ? http://i.imgur.com/nAILfp0.png maybe you are not alone .

 

I will have a read now about this, but my idle is pretty shocking from the start

 

I have read it and some does relate.

Only difference is that with mine no matter what it will go back up to 4000rpm, welllll it ranges between 3000-6000rpm.

The choke did also work normally before.

Also if I look down into the carb when I turn the engine off, it is very very wet and i can see fuel evaporate off it

[_amw_]

Autocock is a great word. They are also quite useful on a motorcycle, when they work!

My Honda CB500 also has a form of autocock to shut off the fuel when the bike is stopped, operated by a vacuum diaphragm.

While you are sorting it out and certainly before you ride the thing I would make sure that the petrol that could have been leaking out of the tank hasn't leaked into the sump and filled it up with petrol. If it has you'll need to drain it all out and throw it away and get some new oil.

This is an easy situation to diagnose as your oil shoudln't smell of petrol and the level shouldn't go up by itself...

[jamessk98]

Autocock is a great word. They are also quite useful on a motorcycle, when they work!

My Honda CB500 also has a form of autocock to shut off the fuel when the bike is stopped, operated by a vacuum diaphragm.

While you are sorting it out and certainly before you ride the thing I would make sure that the petrol that could have been leaking out of the tank hasn't leaked into the sump and filled it up with petrol. If it has you'll need to drain it all out and throw it away and get some new oil.

This is an easy situation to diagnose as your oil shoudln't smell of petrol and the level shouldn't go up by itself...

 

The fuel only ever leaked when the tank was being taken off. So, from the time the rubber pipes were taken off to it being upside down. During that time all that fuel just want all over me really and not the bike

[fastbob]

Then the float valve is sticking open and the carburettor is flooding . This is usually caused by the tiniest particle of dirt or a flake of rust that lodges itself just behind the hole that the rubber point of the float valve needle sits in . If this is the case then this will happen regardless of whether the petrol tap is working or not . However, if you are sure that the petrol tap has been sticking open as well then there is a strong possibility that a lot of fuel will have drained into the oil in the crankcase making it dangerously thin . May I suggest that as a precaution you do an oil change before running the engine for any length of time. Finally, I know you have bought a tank and at a good price too but have a look at this , the price is at the bottom of the page , very small.http://i.imgur.com/2vmYIbm.png one of these might be a good idea while your at it . http://i.imgur.com/ITB64Pf.png

[fastbob]

Apologies to AMW I appear to be repeating your excellent advice concerning fuel draining into the oil . I've been through all this grief myself with my ER5, they are notorious for it .

[jamessk98]

Apologies to AMW I appear to be repeating your excellent advice concerning fuel draining into the oil . I've been through all this grief myself with my ER5, they are notorious for it .

 

Yeah the tank coming has that tap. But if it's still not 100% then i will look further into the carb. Or even get a different second hand one, i can see the adjustment screws have been mangled so everything is most likely way off and god knows what else has been done to it or whatever.

In terms of the oil, how does the petrol get to the crankcase? as wouldn't the only way be for it to go past the piston rings?