I know there have been threads about this before, but thought a reminder to avoid a fire would be a good idea.

When I put my 500F to bed for the winter, I noticed some petrol in the carburettor drip tray and the engine compartment had the smell of petrol. I had a good look around, but couldn't see anything obvious. I made a note to myself to check the float height before putting the car back on the road.

Yesterday, I removed the carburettor cover and checked and reset the float height. On reassembly, I noticed that the hose to the brass fuel inlet pipe appeared to be loose. However, on further investigation, I discovered that the brass inlet pipe was loose in the carb cover. I tapped the pipe back into place, but will be refitting the pipe with Loctite 620 or 640. As an additional safe guard, I will do what some VW owners do, and will wire the hose clips to the carb to ensure that there is positive force holding the brass inlet pipe in position. I will also be doing the same with the inlet and outlet pipes on the fuel pump. One solution would be to tap a thread and fit some threaded inlet pipes, but I don't want to risk trashing a carburettor.

The carburettor on my car looks to be reasonably new, so I wouldn't have much faith in a new one being any better and I'd still be concerned about it coming loose! It's alarming to know that a car could go up in flames because of a poor design that could have been done properly for a couple of cents!

Had the same problem on my 26, loctite is the way. Thanks for the warning.

Is it normal for the inlet pipe to be loose? In the sense that I can rotate it easily....

^^^ No! You should not be able to rotate it with your fingers.

I've encountered loose brass stubs in carbs a few times over the years. Same with the fuel return pipe on cars so equipped. So well worth checking.

I think much thanks are owed to Hobo1960 for bringing this risk to the attention of those who weren't aware of it and also the practical solutions he has offered. Well done

AL.

Some of these brass stubs seem to locked into the carb top cover by a ring of metal being swaged inwards - imagine the stub fitted into position and then placing a close fitting tube over the brass tube against the carb body and hitting it , leaving a circular depression around the brass stub.

Others have 3 swage marks in the alloy around the brass stub, yet others have none of these marks.

I've also encountered these brass stubs with what looks like a ring of epoxy adhesive around it - so presumably others have found a loose pipe and tried to fix it (successfully I'm happy to report ), but a suitable Loctite product would probably be a better choice.

AL.

Another "interesting" fuel pump issue, that I experienced with my Giardiniera and may or may not apply to sedans: On the G the fuel pump is situated at the bottom of the crankcase, and when the membrane becomes perforated (as it must one day), the fuel line forms a syphon that will over time drain the entire content of the fuel tank into the crankcase through the perforation in the membrane.
I've had this happen to me, wondering one morning why the engine wouldn't start or crank properly, when in fact the crankcase was filled to the filler neck with oil/gas mixture. I've since fitted an electric shutoff fuel valve coupled to the ignition coil feed terminal.
It might be worth comparing the levels of the gas tank and fuel pump on the sedan to ensure this cannot happen !

I had a similar problem with a Willy's MB Jeep. Fortunately, I noticed that the oil pressure had dropped by 10 psi, but the engine ran as normal with no signs of the bearings being worn. I pulled the dip stick and could smell petrol so I installed a new petrol pump and the oil pressure returned to normal. I mentioned this to a retired mechanic and he told me that he'd known engines to explode in flames when the fumes in the crankcase ignited. I'm not sure if he was exaggerating, but I could imagine it happening. I think that most of the modern pumps have a small drainage hole to allow any petrol leaking through the diaphragm to drip to the ground.

Your fuel cut off valve sounds like a good idea. I was thinking of fitting one as an anti-theft device and it would also be a safety feature for cutting off the fuel supply if I ever have a fire.

Hobo1960 said:

he told me that he'd known engines to explode in flames when the fumes in the crankcase ignited.

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You can't help the thought crossing your mind, it would really be what you'd call "going with a bang" !

Seen this on a Saab 95 (Ford V4 engine) I saw it stopped with bonnet up and guy in a Tux, so having had one. I did a U turn at a roundabout and stopped just as the cranked it and it went up in flames! I grabbed a extinguisher, put the fire out and then used some Loctite to stick the stub pipe back in. apparently Reliant Scimitar GTE's used to do the same thing, normally at traffic lights and being GRP it was pretty final for the car.
The pipes are normally cast in place. and eventually seem to fall out due to vibration.


Robert G8RPI.

Here's a link to a story on the U.k Fiat 500 Owners Club site. In this case the brass inlet pipe came loose from the fuel pump. The photo's show how lucky the occupants were, Just as well the hood was down!

http://www.fiat500club.org.uk/home/hood-down/

Ok, so best thing would be to put some loctite on the end of the pipe, and then slide it back into place? Should I not worry about the loctite getting into the carb?

Yes, you don't want to get any Loctite inside the carburettor. I've just ordered some Loctite 620 which is designed for interference fit components. I'm going to clean the two surfaces with some acetone. I'll then put a very thin smear of Loctite on the brass inlet tube keeping it well clear of the end that goes deep into the cover, and a thin smear at the top part of drilling. I'm going to keep the glue well clear of the needle valve end of the drilling. I think you'll be fine as long as you're not heavy handed. The tube is an interference fit so a smear of Loctite on a small portion of the tube should give a strong bond. The tube on my carburettor appears to have evidence of sealent being used in the manufacturing process. I've now heard that the new formula of petrol that we use can be detrimental to these sealents. The Loctite 620 is designed to work with unleaded fuel so should hopefully provide a solution to this problem.

Ok, so you're saying to smear some on the outside of the tube, rather then on the end edge, so that when it's slid into the carb, it can adhere to the carb over a larger surface.



Thanks to Chris (bambino) for the awesome carb photos.

Yes I'm going to keep the Loctite as close to your green arrow as possible extending a few millimetres into the drilling. I don't want it anywhere near the float jet. I'll let it reach full strength and test the joint to check it's nice and strong. I may even adopt the belt and braces approach and wire the hose clip to the carb. Apologies, but I'm paranoid about air cooled engines and fires having witnessed two VW's go up in flames!

You had me checking everything because I have never thought of that being a potential problem.
It's obviously more liable to happen if the fuel pipe is putting a strain on the connection. To that end it will probably be worse with the older-style, plastic which goes very hard within a short time.
It will also be best to optimise the lengths of pipe so that any bends are of a reasonable radius.
In my youth I can remember struggling with the removal and re-fitting of the plastic pipes and that aggression probably weakens the joint of the brass. During my time as a lawnmower mechanic (some think I still am one ) I learned that it's easiest to split the ends of the pipe with a sharp blade after removing the clips and to replace with an inexpensive, new piece, using hot water to soften the pipe before sliding onto the brass spigot.
Modern, ethanol-resistant rubber pipes are more flexible and a better option for various other reasons.

I could not help noticing that you say you have a 500F which would originally have been fitted with a Weber 26 IMB 6. It will make no difference but the carb main body in the picture is an earlier possibly IMB 1 or IMB 4. Looks in nice condition though

I found what you were talking about on VW's


https://www.thesamba.com/vw/forum/viewtopic.php?t=525259&postdays=0&postorder=asc&start=0

Where would one attach the safety wire to the carb end? Always on the far screw like the example above?

Where ever you can get the straightest tension without damaging any screws or threads. I may even make up a special angled washer with a second hole to secure a wire.

Peter, I think you're right with your lawn mower hose removal technique. I resorted to a Stanley knife to slit the hose. The removal and pushing on of the fuel hose is definitely a factor in the brass pipes coming loose. I've always been careful pushing the hose on so it's almost touching the carb body as I thought any gap appearing would show that something was loose. This didn't work as the brass inlet must have been moving in and out with each pump stroke!

The carburettor drip tray is a design mystery. I'd like to know how frequently in normal running should petrol find its way there. It's as if Weber accepted that these carbs will flood frequently.

Hobo1960 said:

I had a similar problem with a Willy's MB Jeep. Fortunately, I noticed that the oil pressure had dropped by 10 psi, but the engine ran as normal with no signs of the bearings being worn. I pulled the dip stick and could smell petrol so I installed a new petrol pump and the oil pressure returned to normal. I mentioned this to a retired mechanic and he told me that he'd known engines to explode in flames when the fumes in the crankcase ignited. I'm not sure if he was exaggerating, but I could imagine it happening. I think that most of the modern pumps have a small drainage hole to allow any petrol leaking through the diaphragm to drip to the ground.

Click to expand...

Some of the older 'dismantleable' fuel pumps had twin diaphragms separated by a plastic spacer ring. This spacer ring had a drain hole to the outside of the pump. The thinking was that if the top diaphragm became perforated/split, fuel would leak out through this drain hole, indicating a problem with the pump but that fuel couldn't spill/be pumped into the oil sump. Meanwhile the fuel pump would still function with the remaining diaphragm (minus what would be lost through the drain hole....).

I've seen lots of Mechanics who work on older cars, sniff the dipstick when removed, presumably to check for the presence of fuel in the oil - same as they sniff the auto-transmission dipstick to check for a burnt smell from the trans. fluid.

The crankcase breather pipe that goes to the air cleaner usually has a gauze/wire mesh screen fitted. Some think it's just to seperate out oil from the fumes but it's also a 'flame-trap' (and is often called this in parts lists!). It's function is to prevent a backfire through the carb. from sending a flash of flame back down into the crankcase/sump where it could easily ignite any petrol fumes.

Some petrol can also get into the engine oil due to bypassing the piston rings when the engine runs very rich or on choke. This usually evaporates as the engine heats up and is vented out through the crankcase breather system.

AL.

I also really like what this guy did: