Petrol where oil should be

[Barry]

Out of interest, and to take a very different tack: I've had a number of Guzzi's (leMans, 1100i sport etc) and they run electric fuel taps: ignition on, fuel on, ignition off .... well you can guess the rest.

Anyway, they seemed to be very effective (despite being Italian): a possible solution? Hidden out of the way somewhere of course .

[roy mawbey]

Barry,

If the float valve in one of the carbs fails though wear, the fuel pump working at normal pressure will try to push fuel into the bowl continually and instead of being stopped from doing so by the float rising in the bowl and the needle valve tapered seat sealing the flow, the wear allows fuel to pass the tapered seat overflow the float and send fuel down the the venturi and finally into the oil in the sump.

The fuel pump has a low pressure that if for example is too high could also overide the the needle valve causing the same effect.

It has been said if you fill your tank with petrol, and leave the petcock in the on position and park the car say at 30 degrees up a hill the force of gravity from the fuel tank being full will presumably make enough pressure build up to cause a similar occurance.

I have never had that happen, only read about it. The problem as I see it ( but can of course be corrected ) is the fact petrol overides the fuel valve if its worn when you are actually travelling along in the car, and it probably takes some time for the litres of fuel to get to the oil. How often do you check the oil level?

Maybe someone can clarify it better than me, but thats how I see it.

Roy

[barryb]

Hi

I would have thought that petrol getting into the oil when the car is running ie. hot, it would get burnt off or evaporated. Petrol in the oil I would suspect would occur with a faulty needle valve in the carbs and the petcock not off or a faulty petcock. When stopped residual heat from the engine evaporates the fuel in the carb bowls, that is why there is an insulating block between the manifold and carbs to minimise this. I have never had the problem touch wood. I have however driven off without turning the petcock and come to a sudden and embarrassing stop.

Barry

[roy mawbey]

Barry,

To get "a head" of gravity pressure for a possibly faulty fuel needle valve to allow petrol past the seal, the car would have to be parked up a hill and the petcock in the on position ( Or so everyone says). It wouldn't have helped James if the tank was fully filled but normally the petrol level is not that much above the carbs if at all.

In 39 years of driving without turning off the petcock I never had a problem parking on hills. However for the past 3 years since having the petcock leak and then reconditioning it, I always now turn it off after runs. Barry you might well be correct, possibly extra fuel would just make the engine run rich, and the problem happens somehow when the car is at rest on the level but how? To get litres of fuel and I have seen it for myself when another 356 I had this problem, it must happen over time?

Could the car still run with extra fuel in the cylinder or would it get past the rings direct to the sump?

Anyone know for certain what happens and how?

Roy

[barryb]

Hi

Maybe there is a syphoning effect somewhere, once started it just keeps sucking even with the engine off and on level ground. The sump is lower than the tank.

Barry

[Rustbucket]

I am ashamed to ask but I don't get it.....

why/where would the oil mix with the petrol?

I have always thought that as they are in different circuits all together, for petrol to flow into the oil in that amount, it would have to bypass the pistons or cylinder head?
If too much petrol was flowing in the carbs, wouldn't that only flood the engine?

confused

[roy mawbey]

Don,t be ashamed, it didn't seem logical to me in 1974. I can assure you I could not work out why the 356C I also owned then smelled like a petrol pump. I checked the carbs for external leaks, the fuel pump and all the pipes soft and hard without finding it. Only when seeing the overfilled sump and smelling the dipstick did I get it.

Fuel enters the combustion chamber normally as a fine "mist" its not really in liquid form from the carburetor. This mist is compressed and the engine fires. The mist cannot really get past the rings and down to the sump. However if you were to pour liquid petrol down the venturi of carb it would ( I think? ) travel down the inlet tract and then past the inlet valve that might be open and wash down the cylinder bore past the rings
into the sump?

I suppose its possible if the problem did happen with the engine stationary and the inlet valves were closed the fuel could over time build up in the inlet tract enough to get past the valve set up and into the rocker box. James said his rocker box was also full of oil /petrol.

One guy in the USA said his silencer was half full of petrol to the extent it was drippling out of the exhaust pipe.

Another said he had an hydraulic locked engine becuase fuel had filled the cylinders. Here, I presume?? it must mean there was a very close piston clearance and rings that held the petrol??

I can assure you, my problem was one that took me some time to work out why I had the smell. I was running the car it would start and go.

Surely someone out there can make it clear Could a substancial amount of unmixed with air petrol overflowing a carburetor flow into cylinder and not be burnt and exhausted in the normal way.

Help!!

Roy

[58A - 71E]

Finally got around to sorting this out

Took the carb top off to get to the needle valve and the old one could stick when manipulated, so a new one went in (new one on right, old on left)



Also noticed a distinct wear pattern in the float plate where the valve acts



so polished that out



Time will tell whether this was the cause or not but the findings seem to follow with that thread from the 356 registry - just need to get driving it again

[Dakota]

Hi
did you check the pump pressure and the float height, 356's are quite sensative souls in that respect, that said I had a 356B that seemed to run rather on the rich side and when tested the Snap-on guage indicated eighteen PSI, and it still ran reasonably well...

[john fletcher]

Hi James,
Yes I think you've done the right thing getting rid of the wear mark.
The ball is obviously intended to roll on the the brass plate (wow!).
Someonelse has already mentioned problems with new valves and I can re-iterate that I've had that too and had to revert to the old ones (on a C).
One thing that has not been mentioned is the possibility of the float itself leaking and, well, sinking although if the carb. adjusts OK at idle it's probably not that.

John

[58A - 71E]

One thing that has not been mentioned is the possibility of the float itself leaking and, well, sinking although if the carb John

John you are a star!

I still had problems with petrol in the oil despite a new needle valve so took John's advice and investigated the float - with it in a bucket no obvious pin holes or bubbles, but up against the ear there was a definite sloshing going on inside!

Thankfully I have some old carbs to canibalise for parts so swapped out the floats



The faulty one is the painted gold colour one, the replacement is the black one.

...and I can now report it is finally behaving itself and running great

[hot66]

... and all ready for the yorkshire sunshine & dry roads

[roy mawbey]

James,

So pleased its running okay now. Yes, John is a good engineer, and you were very responsive to his comment by checking the float. Tell me, how much fuel do you reckon was in the float. Good idea to rattle it against your ear as I think it could be very difficult to establish otherwise.

Well done,

Roy

[40 scout]

Good thread - glad it's sorted

Just as an aside - I'm sure there is a definite syphoning effect with these cars -

I leave mine with the petcock off, when I go to start it about a week later, petcock on, turn engine over and it fires straight away but there isn't enough fuel in the carbs for it to run. I assume it evapourates over the week.

I then leave it for 10 minutes or so with the petcock in the on position it will start and run fine then.

Surely this initial turning over of the engine provides enough of a pressure difference to create a syphon effect?

Works for me.

Steve

ps it's amazing how far you can get when you forget to turn the petcock on!

[barryb]

and how embarrasaing when you remember after the initial panic.

Barry