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MG Midget and Sprite Technical - Fuel leak, help please

Hi Guys

I'm looking for some help please as fuel is pooring out and I'm not too keen on driving to a garage in its current situation!

Ok, I have a 1500 midget with twin carbs and for quite some time after a drive I stink of fuel, however I just put that down to it being an old car.

Well today popped the bonnet after a little drive as it was a lot worse and spotted fuel literally pooring out from a cylinder to the right of the dash pot (not sure what its called, 3 screws and a float inside), from what I can see there is a wire wrapped tube coming from the bottom of it to the carbs and I can only imagine its leaking where it connects to the cylinder.

Does this sound about right?

Now I cannot get to it at all, do I have to remove the whole carb assembly from the manifold to inspect and replace it, I can see 4 bolts, 2 at the top but another 2 at the bottom that I think I'd stuggle to get too, so not sure where to go from here?

Any help or advice greatly appreaciated.

Many Thanks
Arron
A Burgess

Arron,
The cylinder with the 3 screw lid is a float chamber which stores fuel before delivering it to the main body of the carb via the spring-covered pipe at the bottom.

The most common cause for leakage is that the needle valve in the lid of the float chamber is not sealing properly when the chamber is full. This may simply be because of dirt on the valve seating. - remove the lid, tilt the float to one side and remove the central part of the needle valve. It will just lift out. Allow a little fuel to wash through to clear any debris. Check the conical end of the needle valve for any visible signs of wear. Reassemble and see if this has stopped any overflow.

The other likelihood is that the little spring covered delivery pipe is leaking where it connects to the bottom of the float chamber. It is a plastic pipe that is a push fit into the bottom of the chamber and then is secured there by a form of compression fitting which is tightened by a brass nut. The "compression fitting" consists of a tiny plastic olive around the pipe and a small washer. Be careful not to loose these small parts. The first thing to do is to slacken the brass nut by a couple of turns, push the pipe firmly into the connection in the bottom of the float chamber and hold it in place whilst you re-tighten the nut. The common mistake is to overtighten the nut which deforms or damages the pipe and causes it to leak, so be careful with this.

Guy
Guy Weller

Cheers Guy that brilliant and detailed advice, just what I was looking for.

I think the second point is probably the most likely as it does seem to be coming from there, its pretty much just pooring out from the bottom of the chamber!

Can you get to this compression fitting whilst the chamber is still in place?

Thanks again
Arron
A Burgess

Arron,

I have in the passed had the same issue an other method of finding out if the valve is closing is to remove the fuel line and with the top of the float pipe removed, blow through the fuel inlet, yes taste that fuel, and then lift the float and see if this prevents air getting in if it does then you know that the float is now sealing before you put it back into the car.

regards

Douglas
df mccabe

Arron,
Yes you can getr at the pipe fitting with the carbs installed although space is very limited and you may need to be working by feel a good deal of the time! Removing the air filter box helps.

The pipe fitting always seemed to me something of a hit and miss sort of a way of making a fuel-tight seal. The brass nut really doesn't have to be over-tightened but as space is limited it is very much easier if you can find a small neat spanner in the proper size. I forget what size it actually is, but have an idea it is something unusual like a whitworth rather than an AF size.

Guy
Guy Weller

a fast little trick that works 80% of the time if its dirt in the valve and not a loose hose

take a platic screw driver handle and rap it on the float chamber with the platic handle several times, many times that will dislodge the debris and save the time to diassemble and clean...a good trick for along the side of a busy high speed traffic road
Prop

Remember, just because you can see the fuel dripping from the bottom of the float chamber, doesn't mean that that is where the leak is. If its the float valve not seating, fuel will flood out of a small "breather" hole higher up the side of the chamber and you will see the sides of the float chamber wet with fuel.( Well, this it what happens on my 1098 with HS2's, not familiar with the 1500)
M J Chapman

further to this

the float overflow hole on top of the float chamber has a thin steel cover that hides it quite successfully from view

Petrol often leaks out of this and drips off underneath the inlet pipe, staying hidden from view

If it is leaking there it's not unknown for the pipe at the bottom to get the blame
bill sdgpm

It is unusual for fuel to leak from the pipe at the bottom unless it has recently been fiddled with, althought it can and certainly does happen.

Try checking the needle valve as described by guy and Douglas and if faulty renew it.

Generally if the pipe connection is leaking at the bottom of the "cylinder" then it will often drain all the fuel from it so that if you remove the lid after the engine has been stopped overnight and the cylinder is empty then it is the pipe that is leaking. If on the otherhand it is full of fuel then chances are your problem is a faulty needle valve.

Hope you have success
Robert (Bob) Midget Turbo

Where in Kent are you ?
A Anstead

Put a pipe on the little thingy that sticks out - and reroute back to the fuel tank - well - if it's like mine ...!
rachmacb

Put a pipe on the little thingy that sticks out - and reroute back to the fuel tank - well - if it's like mine ...!


Rach ...

Are you refering to the brass vent tube on top of the float chamber?

HHhhmmmm if thats correct, You Mean You have those 2 Brass vent tubes on top of the float chamber bowls being tubed/hosed back to the gas tank?

Im not sure ive seen or heard of that before....

Id certianly try removing the tubes from the brass vent pipes as Id think that can cause a restriction on the "pressure" inside the float chamber thus keeping the float valve and float ball from rising up and down vary well....could be part of your carb problems you were experiancing several weeks back

To understand I where Im going...block those brass vent tubes off completely with the engine running...you will see what I mean.

What a great BMC idea.... having all that fuel shooting out all over the super HOY exhaust manifold

Prop
Prop

Prop - there are many things in heaven and earth that you haven't heard of ;)! (yes, another biblical abuse - don't start me!)

However, it is a fairly common "adaption" to prevent the fuel from going all over the exhaust manifold, which, indeed, it does! Not ideal perhaps, but, workable and safe. Or, if you can't be bothered putting it back into the fuel tank - just have it going down onto the ground.
rachmacb

As discussed in another thread, the purpose of the vent tubes in the float chambers is to allow the chamber to vent as the fuel level rises and falls.

Later, it was recognized that fuel vapors venting to the atmosphere was a Bad Thing, and the vents were fitted with hoses leading to charcoal canisters that hold the vapors, drawn through by manifold vacuum.

Unfortunately, in the case of float valve malfunction the chambers fill to the top and raw fuel "vents" from the tubes. The tubes are by no means "overflow" pipes - fuel coming from the tubes is a symptom of insufficient float chamber valving, and must be dealt with.

And besides, owing to the design of the carburetors, too much fuel in the chamber results in an overly rich mixture, which can lead to other issues.

Sorry if I'm stating the obvious here - just thought I'd throw in my tuppence.

-:G:-
Gryf Ketcherside

"Later, it was recognized that fuel vapors venting to the atmosphere was a Bad Thing, and the vents were fitted with hoses leading to charcoal canisters that hold the vapors, drawn through by manifold vacuum"

- Except that is on UK models which were never fitted with charcoal cannisters. In the UK it was thought more appropriate - or more exciting - to allow excess fuel just to pout out - usually over the hot exhaust manifold.
Guy Weller

Rach,

Returning the fuel overflow to the tank sounds a good idea (rather like modern fuel injected engines).

Only drawback that I can see is that you would never be aware that the float chamber was overflowing.

How is it routed back to the tank, in parallel with the supply lines?

Dave
D MATTHEWS

Dave - you can just keep an eye on it, as these things tend to do - there are usually some form of evidence one way or another! It is still a Midget ;)

That's the safest method yes, although, if it is just a little bit of fuel - you can balance out the cost of pipe vs letting it drop to the ground through a shorter length (thereby missing the joy of fuel on the exhaust manifold, which even Prop thinks is slightly dangerous ...!) Me - I ride horses, so have a strange view on danger :)!
rachmacb

<<you can just keep an eye on it>>

How?
Dave O'Neill 2

It's a midget - it'll leak elsewhere - they always do!

It's one of the parts you need to check regularly anyway, so, when you are doing the carbs, then, you'll be able to see what is and isn't leaking.
rachmacb



Gryf is correct, you want to know right away if the valve is working correctly so it can be dealt with right away.

one of the issues I have venting back to tank is if the hose fills completely with fuel it will not allow the float to work properly ...tis could happen if the hose went down ward then rose above the lowest point in the hose aka a sink drain trap...thus not allowing the air to pass

if your conserned about the fuel flowing on the hot exhaust then maybe vent to a vented breatherd catch tank thats close as possiable aka a charcoal canister with vac applied thur the intake manifold

Prop
Prop

A Anstead, I'm in Greenhithe just outside of Dartford.

Looks like its the pipe that is leaking where it connects upto the Float Chamber, called AA homestart out to have a look (was lucky enough to get someone who used to work on Midgets) and he confirmed my suspicions.

I'm sure this is where it is leaking as the chamber is completly dry on the outside, you can only see the fuel coming straight out the bottom and tightening/loosening the nut that holds the pipe on only made it worse.

Disconnected the pipe from float chamber and pulled the jet assembly downwards and it popped straight out of the bottom of the carb leaving the needle on show, I'm hoping the new assembly (ordered from Moss today for 37) will just pop straight back in and I can refit pipe and job done, I think there may be a small bolt that holds it on but could not see one.

Thanks for all the advice, will report back once delivered and I've tried to fit!

A Burgess

Arron,
When they leak there it is usually because they have been overtightened and the end of the plastic pipe has become distorted. Either that or the little plastic olive and washer that slips onto the end of the pipe has gone walkabouts.

Assuming that you have twin carbs, the jet should be attached to the choke linkage arm by a single small screw. If that was missing as well then there is nothing holding the jet firmly against the bottom of the jet adjusting nut. This would really mess up the carburation as the jet would sit too low in relation to the needle and the fuel level in the float chamber, giving an overly rich mixture on that carb.

This would also also allow fuel to flood out of the jet and run down to drip off the bottom of that little tube. Maybe your problems all arise from just that one little screw having dropped out? If you can find a replacement screw (small self tapper I think) you may not need the parts from Moss.

Guy
Guy Weller

If you do need the parts...you will need to re-center the needle and recalibrate the carbs...its not a big deal...just not a 3 minute job.

prop
Prop

Ok, new jet assembly arrived yesterday so I took off the old one to compare...

I noticed that there was a rubber washer missing from my current assembly so refitted old jet with new rubber washer in place and job done no more leaking, I can only imagine that over 30 years or so the old rubber one had perished and fallen out recently leaving me with a drastic fuel leak

New assembly with rubber washer below, just need to order a new rubber washer so I can send back the new jet assembly and get my 33 back.

So, now no leaking but car is really stuttering when you are moving, revs pretty freely at standstill but under load is near undrivable and just stutters, fuel chamber is filling up and I understand I have HS4 carbs so no jet centering needed, pics of my carbs below and any help would be great.

Thanks
Arron
A Burgess

Hopefully pics this time.



A Burgess

and the jet

A Burgess

Arron,
That rubber washer is the "compression fitting with a tiny olive" that I mentioned in my initial reply.

If you have now cured the leak but are getting erratic running I suspect that the carbs now need setting up properly again. It may be that you have unequal jet heights or sticking choke pistons. There are good detailed instructions on setting the carbs on the Burlen Fuels site: http://www.sucarb.co.uk/Technical

Guy
Guy Weller

Arron

Assuming the engine was running OK before this problem, then effectively the set up of the carbs ought to be the same?

In which case something has changed. It is possible to fit the back plate of your air filter upside down. If it is then the poor running would be the result.

Equally topping up the dashpot of one of the carburettors with different oil to the other will also cause the same issue. If you have topped one up then perhaps ypu could drain them both and use the exact same oil in both of them.
Bob Turbo Midget England

And did you locate the missing screw that secures the choke actuating lever to the jet assembly? That would certainly make it misbehave!

Guy
Guy Weller

Aaron. White de bumpered 1500? I think we have met before.
Are you about during the week. I could pop round and have a look. Can't make this W/e.
A Anstead

The only thing that I did was remove the jet assebly and replace, air filter never came off nor were carbs played with which is why I'm confused, maybe the pipe is blocked and not letting fuel to the carb which caused the leak in the first place, will check that tonight?

As for the little screw, there is not one, the jet assembly has a bracket attached with a hole in but it turns out there is a linkage that comes from the carbs with a ball on the end, the ball sits in the hole on the jet assembly and is held on with a little slide on cover, very clever, would not have worked it out unless If I did not have the back carb to look at!!!

Will report back..

A Burgess

A Anstead, no green rubber bumpered 1500, however if you could still pop round that would be brilliant, am around from 7pm during the week or whenever suits you

Pop me your email address and I'll forward over my address.

Thanks
Arron
A Burgess

Hi Aaron
alandotanstead@btopenworlddotcom
A Anstead

So you only took the hose out of the float bowl ... nothing else?


1st see if the carb is getting fuel in the carb FROM the float chamber

2nd look to see if the hose is spiraled twisted

3rd is the hose clear inside...no setiament/dirt inside the hose

4th when you removed the hose from the the float bowl, did it come out freely OR did you have to tug and pull on it, If so how hard?

5th Is the float bowl still in a perfect vertical position ... not angled in anyway ...straight up and down

6th Did you loosen/remove the fuel line 1st, or clamp it off before you started the carb repair?


Prop
Prop

>>>>>>>>>As for the little screw, there is not one, the jet assembly has a bracket attached with a hole in but it turns out there is a linkage that comes from the carbs with a ball on the end, the ball sits in the hole on the jet assembly and is held on with a little slide on cover, very clever, would not have worked it out unless If I did not have the back carb to look at!!!<<<<<<<<<<<


Differant carbs maybe?

closest I can find in my books are SU HS4C carbs definatly a differant choke linkage from the HS4 carbs, and sounds like Arrons discription above

Look at the Dashpot heads...All The Hs4 I have seen looked just like the Hs2 dashpot heads (flat gear shaped), but his are bulbed, not flat

we dont have SU Hs4 carbs on 1500s here in the states, do the dash pots look corrct, if not would they be aftermarkets or an INDICATION of a DIFFERANT carb set up.
Prop

Alan, just sent you a mail, thanks
A Burgess

All fixed, thanks to everyone for their help and advice.

Turned out a rubber gromet had perished, new one fixed the leak, however then had a stuttery engine until I found part of the decomposed gromet blocking the hole at the bottom of the fuel chamber.

Now running as good as ever.

Thanks again
Arron
A Burgess

This thread was discussed between 30/07/2010 and 09/08/2010

MG Midget and Sprite Technical index

This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.