Possible intake leak - Honda CBR 125 2004

Hi,

I apologise if this has been asked, but I did have a look and couldn't find anything similar (i'm at work so can't be searching too long).

But basically I'm having trouble with my idle at the moment. It started off that my idle was surging +- 500rpm. I was trying to set it at around 1600/700rpm.

I thought it might not have been warm enough yet so I decided to go down the road and back, and after it went over 4000rpm it didn't want to go back down. Even if I let go of the throttle completely it would still be happily pulling me up the hill at 3000rpm. Where, normally it would just continue to slow till I would normally stall.

I decided to go to a motorbike garage on the way to work and ask them what it might be. They mentioned it may be an air leak.

So I thought I would ask on here in case somone has had this before and also just for a second opinion, as I don't have much time before I go back up to uni.

Thanks in advance

James

Have a look here.......

https://www.revzilla.com/common-tread/how-to-diagnose-and-fix-an-intake-leak

Sure your throttle cable isn't snagged? Does it alter the revs when you turn the bars?

Yeah, I already tried turning the bars and it made no difference to the engine speed.

It's only when i raise the engine speed above 4000rpm, then just refuses to go below. Even if I put it in first with the brake on and let the clutch out till it goes to 1500, it just comes right back up after I pull the clutch.

And once it's at 4000/5000rpm the idle screw does nothing.

Still sounds like the cable isn't return correctly - especially if the idle adjustment doesn't work.

What happens if you waggle the cable where it attaches to the carb?

Choke stuck ?

Choke stuck ?

I was thinking possibly that as its a bit f**ked as it is. However im not sure as it always has been f**ked and i had made sure it wasn't being pulled at all.

I will have a second look though and put some wd40 on the cable too.

But if it was the choke stuck open, would that not be all the time? as it only happens when i bring the engine speed above 4000, its a nice idle at 4000. Unlike below where it is all over the place. But obviously i dont want a 4000 rpm idle ahaha

Still sounds like the cable isn't return correctly - especially if the idle adjustment doesn't work.

What happens if you waggle the cable where it attaches to the carb?

I just had a wiggle while it ran and it didnt do anything. And the idle screw does work, but only before it goes above 4000rpm

Check the throttle body for the leak, spray some WD40 where it could leak from to check. Also could the throttle body be sticking open?

I thought it was Easy Start that you sprayed to detect intake leaks . The idea being that if there's a leak the revs go up.

Check the throttle body for the leak, spray some WD40 where it could leak from to check. Also could the throttle body be sticking open?

I sprayed some carb cleaning stuff in the throttle, and as i do that it bogs the engine down, what would this suggest?

Also I just saw on the carb, from the previous owner, the other carb screws have been f**ked. so this may have something to do with the problem.

Although I never had this problem mid december when I ran it last, and nothing has changed since, as far as i can think

I thought it was Easy Start that you sprayed to detect intake leaks . The idea being that if there's a leak the revs go up.

I sprayed carb cleaner, also highly flammable, and it just lowered the rpm

I thought it was Easy Start that you sprayed to detect intake leaks . The idea being that if there's a leak the revs go up.

I sprayed it on the joints of the throttle bodies to see if it bubbled, that’s what I was advised to do when I had a fluctuating idle anyway .

I thought it was Easy Start that you sprayed to detect intake leaks . The idea being that if there's a leak the revs go up.

I sprayed it on the joints of the throttle bodies to see if it bubbled, that’s what I was advised to do when I had a fluctuating idle anyway .

I had also done that, was the first thing i did and nothing.

I then took off the inlet rubbers, no cracks or anything

I thought it was Easy Start that you sprayed to detect intake leaks . The idea being that if there's a leak the revs go up.

I sprayed it on the joints of the throttle bodies to see if it bubbled, that’s what I was advised to do when I had a fluctuating idle anyway .

Ok , but its an intake problem so its sucking IN unwanted air not blowing it out .

I thought it was Easy Start that you sprayed to detect intake leaks . The idea being that if there's a leak the revs go up.

I sprayed it on the joints of the throttle bodies to see if it bubbled, that’s what I was advised to do when I had a fluctuating idle anyway .

 

Ok , but its an intake problem so its sucking IN unwanted air not blowing it out .

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 sprayed some carb cleaning stuff in the throttle, and as i do that it bogs the engine down, what would this suggest?

How do you mean "in the throttle"? If into actual throttle body then all it suggests is you've sprayed carb cleaner into the carb if you spray onto carb and around joints (e.g. All the should be sealed places) and it don't affect it then nothing leaking and being sucked in. Leak would have to be inbetween throttle body and combustion chamber, basically it's allowing more air into combustion chamber as if throttle is open wider, normally that would not be sporadic as engine would just suck in as much air as it can get so would be over revving as soon as it fires up.

It does sound more like a throttle cable sticking issue or choke (does it have cable driven choke on bars or is it on the carb itself?)

I sprayed it on the joints of the throttle bodies to see if it bubbled, that’s what I was advised to do when I had a fluctuating idle anyway .

 

Ok , but its an intake problem so its sucking IN unwanted air not blowing it out .

 

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

I sprayed some carb cleaning stuff in the throttle, and as i do that it bogs the engine down, what would this suggest?

 

How do you mean "in the throttle"? If into actual throttle body then all it suggests is you've sprayed carb cleaner into the carb if you spray onto carb and around joints (e.g. All the should be sealed places) and it don't affect it then nothing leaking and being sucked in. Leak would have to be inbetween throttle body and combustion chamber, basically it's allowing more air into combustion chamber as if throttle is open wider, normally that would not be sporadic as engine would just suck in as much air as it can get so would be over revving as soon as it fires up.

It does sound more like a throttle cable sticking issue or choke (does it have cable driven choke on bars or is it on the carb itself?)

I had first sprayed it on the rubbers where i thought the leak may be, then in the throttle itself to see what it would do.

The throttle used to be on the handle bars, but for whatever reason the previous owner moved it under the seat, so no matter what i do to the handle bars it wont move.

I pushed the choke all the way in so it wasnt on at all and not adding extra fuel.

But if i pull on it, the engine bogs down and runs slower

The throttle used to be on the handle bars, but for whatever reason the previous owner moved it under the seat, so no matter what i do to the handle bars it wont move.

 

Surely the throttle is on the bars, do you mean choke

I had first sprayed it on the rubbers where i thought the leak may be, then in the throttle itself to see what it would do.

The throttle used to be on the handle bars, but for whatever reason the previous owner moved it under the seat, so no matter what i do to the handle bars it wont move.

I pushed the choke all the way in so it wasnt on at all and not adding extra fuel.

But if i pull on it, the engine bogs down and runs slower

Take it you mean choke, having a throttle under the seat would be a pain to ride

How has choke been connected under seat? Could that have been a temp fix to a previous issue? Some photos would help.

The throttle used to be on the handle bars, but for whatever reason the previous owner moved it under the seat, so no matter what i do to the handle bars it wont move.

 

 

Surely the throttle is on the bars, do you mean choke

Sorry i was rushing with the reply ahah, now i look dumb as shite.

I believe i have found what the problem is though, i believe the diaphragm is broken. I may or may not have accidentally swaped the lines the wrong way at one point

See attachment.

What diaphragm do you mean ? The one in the carb or the one in the fuel tap ? The red line is around the fuel filter. Don't worry, it takes a while to learn all the correct terminology.

What diaphragm do you mean ? The one in the carb or the one in the fuel tap ? The red line is around the fuel filter. Don't worry, it takes a while to learn all the correct terminology.

Yeah the diaphragm in the tap is the one that supposedly is broken now.

So I ordered a second hand tank off ebay so i can use the tap off that.

What diaphragm do you mean ? The one in the carb or the one in the fuel tap ? The red line is around the fuel filter. Don't worry, it takes a while to learn all the correct terminology.

 

Yeah the diaphragm in the tap is the one that supposedly is broken now.

So I ordered a second hand tank off ebay so i can use the tap off that.

You bought an entire petrol tank to get a fuel tap diaphragm ? Seriously ? You need to show us exactly what you are talking about. No way can I see how a faulty fuel tap is going to cause any of the symptoms that you described in the original post . By the way , I can't even see a fuel tap in the parts diagram that you have posted. There's a fuel outlet and a filter but no tap, automatic or manual to be seen . You need to help us to help you.

Ok , but its an intake problem so its sucking IN unwanted air not blowing it out .

 

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.