25 replies to this topic

[[email protected]]

Hi folks.

 

I have an SU carb that floods my motor.

 

Carb was recently rebuilt by someone who knows his stuff....but why is it flooding my motor? It was not flooding prior to the rebuild.....

 

My apologies but I have been battling to upload pics to the site.

 

My question is simple....the needle from the bottom of the slide does not sit square on the collar. Is this normal??

 

See very bad pics attached. Surely the needle should sit flush with the collar?????

 

Surely the lip on the collar is a factory thing? and why do I just get fuel leaking straight into the manifold?? Been struggling with this foe weeks and am at my wits end and very grumpy. 

 

Any carb experts out there?

 

I will take better pics if someone can help.

 

Thankis

Andrew

 

 

 

Attached Files

•  a1.jpg   20.41K   1 downloads
•  a2.jpg   24.98K   1 downloads
•  a3.jpg   34.96K   1 downloads

[Stevie W]

Hi,

 

If it's a later carb, the needle is "biased" when installed, i.e. its always in contact with the jet bore and will appear to be bent or off centre.

 

If fuel is literally pouring into the inlet manifold, I'd say you have a float bowl issue where the float isn't shutting off the fuel supply and overfilling the float chamber.

 

You need to check the float valve is shutting off the fuel flow. If the float is punctured in some way and isn't floating, this will cause your issue. Too high a fuel pump pressure will also flood the carb.

 

Hope this helps!

 

Regards, Steve.

[MiniMadRacer]

Thats a biased needle, and I think, maybe someone else will correct me but it needs to be fitted biased towards the engine. if its fitted the wrong way round it will over fuel .

[nicklouse]

Pick the correct carb and read the info on your carb.

https://sucarb.co.uk/technical/

[MiniMadRacer]

As per Stevie, we were obviously typing at the same time and he types faster than me.. his advice is a good starting point .

[Shooter63]

This may seem like a silly question, but you have attached the fuel hose to the right ferrule not the vent tube?

Shooter

[timmy850]

The fuel should fill up in the fuel bowl to a certain level. This level should be a few mm short of the top of the jet. The fuel bowl is not under fuel pressure, it should be vented to atmospheric pressure

The fuel is not pushed out of the bowl into the jet and into the engine. It is sucked out of the jet by the air flowing through the throat of the carb.

If the fuel is coming out when the engine isn’t running then either the fuel hoses are incorrectly installed or the valve is stuck and allowing fuel pressure into the bowl and overflowing it

[[email protected]]

Thanks for all your input. 

 

I did have a problem with the needle and seat previously, and the fuel overflowed through the vent/overflow. We replaced needle and seat and this does not happen anymore.

 

The fact that motor is getting flooded (plugs get soaked) means too much fuel? I tried winding in the richness adjuster all the way in and that did not solve the problem.

 

As this was not happening before the expert overhauled the carb for me, I am suspecting that something has not been replaced correctly? Hence I was suspicious of the fit on the collar and needle.

 

My suspicion is either the main jet and needle are very worn and are not sealing, (seating) and too much fuel is being sucked through. 

 

Excuse me sounding like an idiot but this is the first time I have ever looked at an SU carb.

[Stevie W]

You don't sound like an idiot, that's why this great forum is here, to try and help like minded Mini owners out 

 

Might be worth checking the choke mechanism is working correctly as on the SU carb, the jet is moved downwards when you pull out the choke control. If the jet doesn't return fully as you push the choke control in, the engine will flood with excess fuel.

 

Cheers, Steve.

[KTS]

You don't sound like an idiot, that's why this great forum is here, to try and help like minded Mini owners out 

 

Might be worth checking the choke mechanism is working correctly as on the SU carb, the jet is moved downwards when you pull out the choke control. If the jet doesn't return fully as you push the choke control in, the engine will flood with excess fuel.

 

Cheers, Steve.

 

unless it's an HIF type carb in which case the choke mechanism/operation is different, but the point is still well made

 

some detail on what type of carb it is would help

[Ethel]

What type of SU is it? HS with a separate float bowl connected by an external line to the jet, or HIF where the float is in the bottom of the main body & encloses the jet?

 

What sort of fuel pump to you have, mechanical, or electric?

 

The float valve not functioning properly, for whatever reason, is the only way* it'll flood - assuming the carb is anything like horizontal.

 

It could run rich if the jet/needle are worn, mismatched, or badly adjusted, But, you'd likely still be able to adjust it to be right if only at idle.

 

If the dashpot can't rise freely it will run richer under load. Test manually, make sure the communication ports aren't blocked by elbow/filter gasket!

 

*...unless it is a HIF with a leaking choke.

[Stevie W]

 

You don't sound like an idiot, that's why this great forum is here, to try and help like minded Mini owners out 

 

Might be worth checking the choke mechanism is working correctly as on the SU carb, the jet is moved downwards when you pull out the choke control. If the jet doesn't return fully as you push the choke control in, the engine will flood with excess fuel.

 

Cheers, Steve.

 

unless it's an HIF type carb in which case the choke mechanism/operation is different, but the point is still well made

 

some detail on what type of carb it is would help

 

 

Good point, I failed to ask what type of SU carb it was HS or HIF!

 

Cheers, Steve.

[[email protected]]

I tries research on the serial number on the carb but can't find it online.  I also looked at the doc provided by nicklouse above (thanks Nick) but the pics show a a fixed connection between the carb and bowl.

 

This carb has a flexible pipe connecting the bowl to the bottom of the mainjet. Metal casing around the pipe not sure what is inside it. 

 

I have no pump. It is gravity fed from a tank that is situated above the motor. Plastic inline filter. After I tried to fire up the engine the flooding was so bad to the point to where there was a little pool of fuel in the intake manifold. 

 

I am going to reinstall the carb tomorrow and check (from your guys comments above) that the fuel is not just flowing unchecked from the bowl past the mainjet. So If I install the carb without the slide and needle and the fuel does not bubble up through the main jet then thats not the problem? Or does it need the needle in place to restrict fuel flow? I realise that the air flow through to the engine should suck the fuel up and then vaporise it and send through the manifold.

 

If it doesnt bubble through I wiil then assume that the mainjet or needle is so worn that far to much fuel is being let through. Is that a reasonable assumption? Any ideas on how to test that?

 

My problem is that I live in the bush 5 hours from the nearest city where I could have it looked at. ( I couried the carb to the big city and back....cant do that withe whole vehicle

 

Really appreciate the advice and help you folks are giving me....I am getting closer....and hopefully I can share my own advice with someone else further down the line.

 

Cheers

Andrew

[Chris1275gt]

I’ve found this book very useful available on Amazon or EBay

Attached Files

•  BDFA505F-CBE1-457B-ABC7-10E94B0402D0.jpeg   92.72K   1 downloads

[Lplus]

I tries research on the serial number on the carb but can't find it online.  I also looked at the doc provided by nicklouse above (thanks Nick) but the pics show a a fixed connection between the carb and bowl.

 

This carb has a flexible pipe connecting the bowl to the bottom of the mainjet. Metal casing around the pipe not sure what is inside it. 

 

I have no pump. It is gravity fed from a tank that is situated above the motor. Plastic inline filter. After I tried to fire up the engine the flooding was so bad to the point to where there was a little pool of fuel in the intake manifold. 

 

I am going to reinstall the carb tomorrow and check (from your guys comments above) that the fuel is not just flowing unchecked from the bowl past the mainjet. So If I install the carb without the slide and needle and the fuel does not bubble up through the main jet then thats not the problem? Or does it need the needle in place to restrict fuel flow? I realise that the air flow through to the engine should suck the fuel up and then vaporise it and send through the manifold.

 

If it doesnt bubble through I wiil then assume that the mainjet or needle is so worn that far to much fuel is being let through. Is that a reasonable assumption? Any ideas on how to test that?

 

My problem is that I live in the bush 5 hours from the nearest city where I could have it looked at. ( I couried the carb to the big city and back....cant do that withe whole vehicle

 

Really appreciate the advice and help you folks are giving me....I am getting closer....and hopefully I can share my own advice with someone else further down the line.

 

Cheers

Andrew

The float and needle valve should stop the fuel flow before it reaches the level of the top of the jet.  Also the pipe from float bowl to jet is a plastic tube inside the coiled metal sleeve.