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MG MGB Technical - Fuel Leak in Engine bay

I have asked this before but still totally perplexed after months of trying, now going mad over this. When i drive my 74 gt round right hand bends the fuel pump "clicks" like mad and the i get a smell of fuel in the car. It does not happen on left handers.

I have done the following;

Replaced fuel pump, all fuel lines fixed and flexible, filter, checked the carbs (HIF) for leaks (none), checked fuel lines for leaks (none), cant see any fuel leaks in engine bay lines, no evident fuel leaks or marking anywhere in the engine bay, or around the fuel tank. I cant see a leak as it only happens on right hand bends, and its impossible to look at the engine bay whilst driving round bends (did ask the wife but she refused!).

My question is, why is the fuel pump (electronic pump) clicking faster on right hand bends, and where could the fuel be leaking?
whiskeyfrank

The only thing I can suggest is that you keep driving round in circles e.g. in a supermarket car park out of hours until the leak *does* show. If it is big enough to make the pump click noticeable faster it *must* be significant, and therefore must leave some evidence, especially if the engine bay is relatively cool at the time.
Paul Hunt 2

If you have HS4 carburetors, you could have a float that is dropping during hard turns due to the way it is hinged. It is my understanding that tis is a rather common occurance with the HS 4 carbs. there is a SU carburetor guru here in the US that has a modified float arrangement that is similiar to the floats in the T series cars and MGAs that corrects this problem. the gentleman's name is Joe Curto an his web site is at: http://www.joecurto.com/ It might be that the modification that he carries is something that Burlen Fuel Systems has also, it would be worth dripping Joe a note.

The other possibility is that you have a partially flooded float, which would be much easier to check and correct. Cheers - Dave
David DuBois

with it been a gt there is a poss that it is in the boot area either the filler tube is loose or a problem with the breathr lines in the boot floor
on other is you have holes in the top of your tank and its fuming into the car
ste
Ste Brown

Could be 2 different problems with the same cause.As you go round a right hand bend,the fuel moves to the left side of the tank a]finds hole in tank,leaks and hence the smell b]surge causes pickup starvation hence the pump running fast.I recently had a bad carb leak with no smell in the car, I would therefore suspect a leak other than the engine bay and would be looking at the tank given all the other work you have done.Good Luck, Peter
Peter Jones

I'm interested in this discussion, because I too have some fuel problems. 72B. (I see this got long, as usual - sorry!)

I routinely smell gas in the trunk, whether full or near empty tank. I've tightened clamps on rubber hoses in trunk below filler cap. I've checked hoses on vapor canister in trunk. And cap goes on tight. All appear fine. Yet the smell. Can't keep much in the trunk without it collecting fumes. But some days there's nothing.

The above chain of posts implies there could be small holes in the top of the tank causing the fumes. That should be fun to chase down! Others have raised concern for hoses to vapor canister that may appear intact, but may actually allow vapors to escape.

The other problem, which I thought had gone away, is very bad gas mileage.

I, a month ago completed a valve job (very bad exhaust valves/seats). The car is amazingly improved in performance. And the gas mileage appeared to be quite improved, just based on watching the gauge not dropping as fast as before.

I don't have an exact gas mileage to compare to as I also swapped out speedometers during this time. But the change in gas consumption and reduced rich smell implied my gas mileage was on the mend.

This has been a good 200 miles on a partial tank. So now with new speedometer, checked for accuracy too; I filled the tank yesterday, as gauge was almost on empty. It took a good 10 gallons. Which seemed appropriate.

Last night I changed front brake hoses and took car on a 4 mile test. All seemed fine.

Today I drove about 20 miles and I noticed gas gauge around 3/4 and now 10 -15 miles later I'm reading 1/2 tank. So according to the gauge I'm at 40 miles for 1/2 a tank.

I've gone over tank for smells, signs of leaks on sides and bottom - nothing.

I have car parked on cardboard, routinely - nothing.

I've just gone over hoses underhood, at elec fuel pump, gas filter, carbs, etc. I cannot locate a single spot of stain anywheres (I thoroughly degreased engine when doing valve job, anything would show up.).

Of course tomorrow I'll go to the gas station and refill tank - to see if it is the gauge.

But car appears to run fine, yes it may lope (sp?) or idle unevenly like I have a slightly modified cam in it but it starts fine, accelerates fine. But now I'm wondering if it smells rich again.

Your thoughts please!
R.W.Anderson

Robert,

It's very difficult to consistently fill the tank on the MGB as it is hard to tell when you are filled. The earlier you fill your tank (and the less gas you need), the more inaccurate your readings will seem to be. On the MGB I routinely care for, the fuel milage will vary between 23 and 29 mpg depending on the accuracy of the previous and the current fill.

Make sure your charcoal canister is not flooded out (part of the evaporartive control system) and assure that the level of the fuel is about an 1/8th inch below the bridge in the throat of the carburetor. If not, adjust the float. Adjust the mixture so that lifting the piston 1/32 of an inch increases the engine speed momentarily, and then slows it down.

I hope that you are able to trace your fuel smell, but my advice is to start with the evaporative system. Overfilling the tank is a good way to flood that canister, by the way.

dave
Dave Braun

Nothing new here, but just emphasizing some points already made. Having checked all the lines, my next steps would be:

1. check the carb floats. On one occasion, I had an HIF carb float develop a pin-hole sized leak. It eventually filled with fuel and sank. Now in my case, there was obvious spilled fuel in the engine bay, but even a very small leak can cause a STRONG smell.

2. the braided lines from the tank to the vapor seperator (inside right rear wing) can deteriorate and leak vapor, if nothing else. Of course with the braiding, leaks in these lines are not easily detected. Remember, to get the smell, this system needs only to leak vapors, not necessarily raw fuel.

3. These post '64 fuel tanks are notorious for rusting out on top and leaking. They can leak so slightly that you may never find evidence of actual fuel leaking, but the car will stink like crazy. Maybe if you try Paul's very good suggestion of doing lots of hard right circles in a parking lot, eventually you might find a little fuel near the top of the tank on the left side. If your car has been undercoated, sometimes the old undercoating will absorb some of the leaking fuel such that you might not see it even though it is leaking. You might try Paul's trick with a full tank, and then with only half a tank. If you notice a difference, I think you may have found the problem.

Of course, Robert, part of your problem might be that those hills in Stillwater are way beyond the design parameters of SU carburetors which were not designed to feed correctly when the car is going up or down a 90-degree grade.

Seriously, folks, Stillwater Minnesota has hills that make San Francisco's Lombard Street look like a section of Kansas interstate.

FWIW,
Allen

Allen Bachelder

I'll try the above suggestions, and check out the floasts too.

Just when I thought I could relax inbetween repair jobs for a week or so!

And to the remark about Stillwater having big hills. I would point out that most downhill streets do not have stops signs - its the cross streets, for a good reason. One street is closed off in winter as being too steep to stop on and it intersects another steep hill at the bottom - which makes for some interesting meetings at the intersection. Yeah-what's the big deal about streets in San Fran anyway!
R.W.Anderson

OK tried the carpark turning, and apart from some comments as to why an old car is trying (and failing) to do doughnuts, I still havnt got anywhere.

To clear up the fuel tank possibility, its a new tank and i have looked at the entire systems and its a clean as new. One thing that makes me think its the engine bay is that the smell is worse when ive got the heater on, with the blower its worse.

I could not see any fuel marks, no damp marks or fuel spills in the engine bay. I cleaned the carbs and dusted them with talc (getting desperate now) and they were clean and dry but the smell persists.

Getting to the "haunted car" stage now!

whiskeyfrank

Frank,

Driving the car hard, I used to lose fuel from the filler pipe. I replaced the cap, but ended up replacing the filler tube and cured the problem. A temporary test-fix is to put a double or treble thickness of supermarket carrier bag over the filler tube and replace the cap - that even stopped fuel coming out during autotests...

Fuel will go to the left of the tank during a right hand bend hence the clicking as the pick-up is on the right hand side - and then slosh back to the right as you straighten up and out of the filler pipe. Maybe you should try Paul's test only anticlockwise!

Neil
Neil Lock

Within 30+ years of MG B driving, i have learned why there was the adwise to renew all the rubber parts within 48 month of use. O.K. i never met anybody who followed this adwise and it takes many years until problems beginn, but be sure, they knew what they were talking and thinking about.

It is not a difficult job to renew all the rubber connetions in the fuel system and fit new floats to the carbs too, service the pump with new points and a new diaphragm. There are still some areas at the tank to be checked: corrosion on the top of it, a leaky sender unit and a corroded soldering of the fitting of the fuel line at the side of the tank, hard to see but if the system has been presurized with compressed air, all these falts will be found. On my V8 the problem started 26 years after delivery and is solved now. The roadster had the same falts after 27 years of use. Seems to be quite normal, does it?

Ralph
Ralph

You say you have dusted the carbs with talc, but if you have the correct vent pipes and it *is* the float opening the valve when it shouldn't be, there *won't* be any fuel spillage at the carbs, just leakage from the bottom of the vent pipes. As such it is a relatively simple exercise to tape a little catch bottle to the bottom of the pipes and see if you get any inside.

If it worse with the heater on, particular the blower, that implies the seal at the rear bonnet edge is defective, and you will be getting all sorts fumes potentially coming from the engine compartment.
Paul Hunt 2

Paul, excuse my ignorance, where are the vent pipes on a HIF4 carb?

Also just checked the seal and its looks OK, i will renew it anyway as ive done everything else so may as well.
whiskeyfrank

Can't say specifically for the HIFs on a 4-cylinder as mine has HSs. The V8 does have HIFs, and the vents exit the carb body sideways and in opposite directions, which would equate to forwards on the front carb and backwards on the rear carb for a 4-cylinder. That means two ports on the same side (nearest the front) on the front carb. The front carb should have a 3rd port, on the rearward side, which is the fuel feed from the front carb to the rear carb. The rear carb then has a single port on the other side (i.e. towards the rear of the car) which is its vent pipe. On the front carb the vent pipe is closer to the engine than the fuel feed pipe, and Clausager indicates that on UK cars they turn downwards, so I'd expect them to follow much the same path as the HSs i.e. via a bracket near the front engine mount.
Paul Hunt 2

This thread was discussed between 18/05/2007 and 25/05/2007

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