32 replies to this topic

[Tamworthbay]

There isn't much else that can be wrong, the only parts involved are the needle assembly and float. How is the fit of the needle in its hole.,perhaps the hole is very worn and either the needle is sticking or fuel is escaping past the seat (but if you can't blow down it when it's closed I can't see how that could happen). Beyond that it's hard to think what could cause it, if you had recently changed the fuel pump I would suggest pressure could be too high. Do you know anyone who could lend you a float chamber top to try on yours to see if that solves it?

[1984mini25]

Unless the jet in the carb is partially blocked, witch I've had quite a few times before fitting a filter. Easiest way without having to completely dismantle the carb is to remove the dash pot and piston, remove the float valve lid, cover the carb with a clean rag and blow the jet through with compressed air.

 

The mechanical fuel pumps are pretty reliable, they only deliver about 3 psi witch is all you really need with a carb. The only times they fail is when they stop working completely or leak fuel directly into the gearbox/sump and engine oil.

[mkw]

There isn't much else that can be wrong, the only parts involved are the needle assembly and float. How is the fit of the needle in its hole.,perhaps the hole is very worn and either the needle is sticking or fuel is escaping past the seat (but if you can't blow down it when it's closed I can't see how that could happen). Beyond that it's hard to think what could cause it, if you had recently changed the fuel pump I would suggest pressure could be too high. Do you know anyone who could lend you a float chamber top to try on yours to see if that solves it?

 

That's what I can't understand, its such a simple system and i've tried all the obvious stuff but nothing is working

[mkw]

Unless the jet in the carb is partially blocked, witch I've had quite a few times before fitting a filter. Easiest way without having to completely dismantle the carb is to remove the dash pot and piston, remove the float valve lid, cover the carb with a clean rag and blow the jet through with compressed air.

 

The mechanical fuel pumps are pretty reliable, they only deliver about 3 psi witch is all you really need with a carb. The only times they fail is when they stop working completely or leak fuel directly into the gearbox/sump and engine oil.

 

If the jet is blocked why would that cause fuel to leak from the overflow? I don't mean that to sound like i don't trust the advice by the way!

 

I will try that, i've got a compressor so it's worth a shot.

[1984mini25]

 

Unless the jet in the carb is partially blocked, witch I've had quite a few times before fitting a filter. Easiest way without having to completely dismantle the carb is to remove the dash pot and piston, remove the float valve lid, cover the carb with a clean rag and blow the jet through with compressed air.

 

The mechanical fuel pumps are pretty reliable, they only deliver about 3 psi witch is all you really need with a carb. The only times they fail is when they stop working completely or leak fuel directly into the gearbox/sump and engine oil.

 

If the jet is blocked why would that cause fuel to leak from the overflow? I don't mean that to sound like i don't trust the advice by the way!

 

I will try that, i've got a compressor so it's worth a shot.

 

 

If you look at how the fuel system works. You have a mechanical pump on the back of the engine that's driven off the cam, so the faster the engine revs the more fuel is delivered as required. The pump is then connected to the carb via a float bowl, witch has a float valve and needle to prevent the carb overfueling and diverts any excesses that isn't needed.  

 

So if the jet in the carb was even partiality blocked, the engine wouldn't be getting enough for it to run properly (or at all) the float bow would fill lifting the float valve off its seat blocking off the fuel supply to the float bowl/carb.  But that eases fuel has to go somewhere, as the pump will continue to run as long as the engine is. So as the needle valve is lifted off it seat blocking off the fuel supply it then diverts it out of the overflow, until the level in the float bowl is low enough for the float to drop an close the needle valve.

[mkw]

 

 

Unless the jet in the carb is partially blocked, witch I've had quite a few times before fitting a filter. Easiest way without having to completely dismantle the carb is to remove the dash pot and piston, remove the float valve lid, cover the carb with a clean rag and blow the jet through with compressed air.

 

The mechanical fuel pumps are pretty reliable, they only deliver about 3 psi witch is all you really need with a carb. The only times they fail is when they stop working completely or leak fuel directly into the gearbox/sump and engine oil.

 

If the jet is blocked why would that cause fuel to leak from the overflow? I don't mean that to sound like i don't trust the advice by the way!

 

I will try that, i've got a compressor so it's worth a shot.

 

 

If you look at how the fuel system works. You have a mechanical pump on the back of the engine that's driven off the cam, so the faster the engine revs the more fuel is delivered as required. The pump is then connected to the carb via a float bowl, witch has a float valve and needle to prevent the carb overfueling and diverts any excesses that isn't needed.  

 

So if the jet in the carb was even partiality blocked, the engine wouldn't be getting enough for it to run properly (or at all) the float bow would fill lifting the float valve off its seat blocking off the fuel supply to the float bowl/carb.  But that eases fuel has to go somewhere, as the pump will continue to run as long as the engine is. So as the needle valve is lifted off it seat blocking off the fuel supply it then diverts it out of the overflow, until the level in the float bowl is low enough for the float to drop an close the needle valve.

 

 

So, i've done as you suggested. Got some mucky looking crap out and then kept on blowing till all was clear. Started the car up and again, flooding then stutters to a complete stop.

 

Anything else?

[carbon]

How close did you manage to fit the in-line fuel filter to the carb?

[mkw]

About 6" away.

[Tamworthbay]

I would try and get a spare float bowl top and try that. Best is to borrow that's known to be ok, but HS4s are cheap so ypu could see if you could pick one up.

[1984mini25]

 

 

 

Unless the jet in the carb is partially blocked, witch I've had quite a few times before fitting a filter. Easiest way without having to completely dismantle the carb is to remove the dash pot and piston, remove the float valve lid, cover the carb with a clean rag and blow the jet through with compressed air.

 

The mechanical fuel pumps are pretty reliable, they only deliver about 3 psi witch is all you really need with a carb. The only times they fail is when they stop working completely or leak fuel directly into the gearbox/sump and engine oil.

 

If the jet is blocked why would that cause fuel to leak from the overflow? I don't mean that to sound like i don't trust the advice by the way!

 

I will try that, i've got a compressor so it's worth a shot.

 

 

If you look at how the fuel system works. You have a mechanical pump on the back of the engine that's driven off the cam, so the faster the engine revs the more fuel is delivered as required. The pump is then connected to the carb via a float bowl, witch has a float valve and needle to prevent the carb overfueling and diverts any excesses that isn't needed.  

 

So if the jet in the carb was even partiality blocked, the engine wouldn't be getting enough for it to run properly (or at all) the float bow would fill lifting the float valve off its seat blocking off the fuel supply to the float bowl/carb.  But that eases fuel has to go somewhere, as the pump will continue to run as long as the engine is. So as the needle valve is lifted off it seat blocking off the fuel supply it then diverts it out of the overflow, until the level in the float bowl is low enough for the float to drop an close the needle valve.

 

 

So, i've done as you suggested. Got some mucky looking crap out and then kept on blowing till all was clear. Started the car up and again, flooding then stutters to a complete stop.

 

Anything else?

 

 

If its now over fuelling with the cleared jet, it could need the nut on the bottom adjusting to lean the mixture off.

[Tamworthbay]

Unless the jet in the carb is partially blocked, witch I've had quite a few times before fitting a filter. Easiest way without having to completely dismantle the carb is to remove the dash pot and piston, remove the float valve lid, cover the carb with a clean rag and blow the jet through with compressed air.
 
The mechanical fuel pumps are pretty reliable, they only deliver about 3 psi witch is all you really need with a carb. The only times they fail is when they stop working completely or leak fuel directly into the gearbox/sump and engine oil.

 
If the jet is blocked why would that cause fuel to leak from the overflow? I don't mean that to sound like i don't trust the advice by the way!
 
I will try that, i've got a compressor so it's worth a shot.

 
If you look at how the fuel system works. You have a mechanical pump on the back of the engine that's driven off the cam, so the faster the engine revs the more fuel is delivered as required. The pump is then connected to the carb via a float bowl, witch has a float valve and needle to prevent the carb overfueling and diverts any excesses that isn't needed.  
 
So if the jet in the carb was even partiality blocked, the engine wouldn't be getting enough for it to run properly (or at all) the float bow would fill lifting the float valve off its seat blocking off the fuel supply to the float bowl/carb.  But that eases fuel has to go somewhere, as the pump will continue to run as long as the engine is. So as the needle valve is lifted off it seat blocking off the fuel supply it then diverts it out of the overflow, until the level in the float bowl is low enough for the float to drop an close the needle valve.

 
So, i've done as you suggested. Got some mucky looking crap out and then kept on blowing till all was clear. Started the car up and again, flooding then stutters to a complete stop.
 
Anything else?

 
If its now over fuelling with the cleared jet, it could need the nut on the bottom adjusting to lean the mixture off.

wouldn't the excess fuel just go into the engine? So he would see black plugs, rough running, black exhaust etc if that was case. Apologies if I am being ignorant but I can't see how it's linked to the overflow system.

[1984mini25]

 

 

 

 

 

Unless the jet in the carb is partially blocked, witch I've had quite a few times before fitting a filter. Easiest way without having to completely dismantle the carb is to remove the dash pot and piston, remove the float valve lid, cover the carb with a clean rag and blow the jet through with compressed air.
 
The mechanical fuel pumps are pretty reliable, they only deliver about 3 psi witch is all you really need with a carb. The only times they fail is when they stop working completely or leak fuel directly into the gearbox/sump and engine oil.

 
If the jet is blocked why would that cause fuel to leak from the overflow? I don't mean that to sound like i don't trust the advice by the way!
 
I will try that, i've got a compressor so it's worth a shot.

 
If you look at how the fuel system works. You have a mechanical pump on the back of the engine that's driven off the cam, so the faster the engine revs the more fuel is delivered as required. The pump is then connected to the carb via a float bowl, witch has a float valve and needle to prevent the carb overfueling and diverts any excesses that isn't needed.  
 
So if the jet in the carb was even partiality blocked, the engine wouldn't be getting enough for it to run properly (or at all) the float bow would fill lifting the float valve off its seat blocking off the fuel supply to the float bowl/carb.  But that eases fuel has to go somewhere, as the pump will continue to run as long as the engine is. So as the needle valve is lifted off it seat blocking off the fuel supply it then diverts it out of the overflow, until the level in the float bowl is low enough for the float to drop an close the needle valve.

 
So, i've done as you suggested. Got some mucky looking crap out and then kept on blowing till all was clear. Started the car up and again, flooding then stutters to a complete stop.
 
Anything else?

 
If its now over fuelling with the cleared jet, it could need the nut on the bottom adjusting to lean the mixture off.

wouldn't the excess fuel just go into the engine? So he would see black plugs, rough running, black exhaust etc if that was case. Apologies if I am being ignorant but I can't see how it's linked to the overflow system.

 

 

 

The way I'm reading it.

 

Originally it was the carb overflowing, replaced needle valve with same symptoms and an engine being starved of fuel and staling.

 

I've suggested a blocked jet reducing fuel flow and causing the carb to overflow.

 

The jet has now been cleaned and from what I can gather the symptoms are that the carb is no longer overflowing? But its running so rich with the cleared jet its over fuelling (or too much choke) to the point its stalling.

Edited by 1984mini25, 14 January 2015 - 01:40 PM.

[mkw]

No, the car is still pissing fuel out as before

[miniman3003]

Did you renew just the needle valve only or both the valve and the brass seating? They should always be renewed as a pair.

[nicklouse]

It sounds like there is confusion going on here.

The float chamber valve (needle) will stop the fuel from the pump entering the float chamber if it is full such as low revs.

Think of you toilet sane idea the pressure is always there but does not pass.

Hence the pump question earlier as the needle will not stop the fuel at a higher pressure of many electric pumps.

If the carb needle is full of crap etc it will have no bearing on the float overflow passing fuel.

There are only two things. Too much pressure or a faulty (dirty) float chamber valve.

There is a third option. Is this a replacement carb? Are you sure is is a single carb and not one of a pair with fuel take off/inlet for a second carb?

I think we are at a pictures time. Arrows of where fuel is coming out would be excellent.