Hey folks, car's been dumping gas out of the float bowl overflow pipes, tank had lots of rust.

While waiting for all the bits to rectify it all I've had to drive the car, and am concerned about whether any damage to the engine is likely. It would start and run fine, then after shutting it off for some time, upon restarting it would stumble under acceleration for a bit until it cleared up.

I could see fuel coming out of the overflow pipes, and so I tried new needles/seats, new fuel pump (it had an aftermarket pump rated 5-9 lbs., and I thought this was the cause), and looked down tank filler neck and it looked clean, so I (quiet mistakenly) kept thinking since I had a fresh fuel filter, it must be the pump or carbs...

...then when replacing a washer on the tank-side banjo connection on the new SU pump, I saw sediment in the threads...ok now it's clear what's going on.

Upon draining the tank, the mostly destroyed screen on the plug was totally displaced, and looking into the float/sender hole there's lots of rust, dirt and ok, new tank on the way.

So I was told by the seller (retired Jag mechanic) that in this case all the fuel dumps to the ground...is it true, or did the +/- 200 miles of use do no favors to the engine?

Thanks in advance!

 

Make sure your new needles are Viton tipped. If fuel is running out of the plenum chamber drains then one or both carbs are flooding.

It can only be caused by excessive fuel pump pressure or a leaking needle & seat, float/fuel level too high or sinking floats due to a leak allowing them to fill with fuel. Then they sink or partially sink & do not shut the needle & seat leading to flooding.

SU carburettors work well with fuel pressure in the range of 1.5 psi to 3.5 psi at the inlet to the float chamber. Pressure of 5 psi or higher will likely make the fuel overflow. The original SU electric fuel pump has an internal spring on the operating solenoid that effectively limits pressure to the intended range.

The entire system must be spotlessly clean ~ no rust particles or other debris.

Change your oil. It might be diluted by fuel. You are probably just fine if it was only 200 miles.

 

Buy this book. It is cheap.

 

Hey Glyn, thanks for that. All this started after I'd done a complete change of all lubricants, and I've already changed the oil once more about halfway thru this little debacle - costly, yes but in the long run it's likely better than not doing so I reckon.

Upon inspection, the (quite dry inside) quality brass floats, viton-tipped needles and seats appeared to have been very recently changed. There was a small bit of sediment present in the bowls, and the only other thing of note was that one carb's mixture had been set quite rich.

I'd been advised to replace the float needles with "Gross jets", which I now have...they are supposed to be a vast improvement over even the viton-tipped units. Are you familiar with them?

Again, thanks for your prompt reply!

 

The float needle argument goes on and on. I have no particular preference. I am running Viton tipped needles and they seal very well. Zero issues. My Viton tipped needles are made in Australia. Not by Burlen.

 

Jagman, Somerset West, Cape Town (Gerald Williams) imports his SU Rebuild kits (jets, diaphragms & all) from Australia at a price more reasonable than Burlen. Everybody here uses them and he has not had a single complaint. I turfed the boxes in the trash and don't remember the Brand. It's a while back now. They tolerate the 10% Sasol fuel alcohol in our highvelt fuel with no issues. I'm now out of the alcohol fuel area. We have our own refinery in Cape Town from crude & not coal gasification based fuel from the Sasol process.

What doesn't tolerate the alcohol is the pipework sold as "the right stuff" by many (which I suspect is PVC as Peter has mentioned). The genuine original Nylon tubing used by Jaguar tolerates alcohols very well.

My car after 2 weeks of Sasol fuel alcohol.

 

Chris, I'm familiar with Gros Jets, I had them in my 51 Bentley and my 340 Jag.

They seem to work fine for a season, but they later stuck shut or open, they became impossibly sticky where after removal to try and free them up; they would not.
I used brake cleaner, lacquer thinner, acetone, paint thinner... _ nothing worked.

On hot days both cars would flood, and on the Jag, the starting carburetor would over flow especially after sitting _ didn't matter what jets were in there, but worse with the Gros Jets.

The Bentley had this impossibly small breather tube from the fuel tank, and the Jags breather tube wasn't much better.
I enlarged them both and made them shorter, this seemed to allow any fuel expansion to escape through the breather tubes rather then putting pressure on the fuel delivery system.
So my theory was, and it appears to be working.
It still is a little bit of a problem, but no where near what it was.

 

Hey Jeff, thanks...

I'm beginning to wonder if I'm experiencing some of the same issue, re. fuel tank venting...the car came with the original non-vented cap, and I replaced it with a vented one. It wasn't until I removed the tank that I noticed the breather pipe...maybe it's clogged. The new cap should be doing the job now, but this area may be contributing to the fumes in the cabin....who knows.

When I get the new tank, assuming it'll have the vent spigot I reckon I'll run a hose to the ground and replace the non-vented cap...just to start from scratch with everything std. issue.

We'll see ..

 

In July 1960, two changes were made to counter complaints about petrol smells in the car: a breather pipe was fitted to the filler neck, together with a non-vented filler cap. I would clean & enlarge the breather as Jeff suggests and use a non vented cap.
Source ~ Technical Bulletins & scribes.

 

Refresh page for edit.

 

Chris, you want to run the fuel tanks' vent line away from the car, just letting it hang down will allow the fuel vapors to collect in the under carriage of the car.

As Glyn says about the fuel smell in the car.
Someone had added a vented cap on mine and the boot always smelled of fuel, this was made worse as it already had the vented line system, but the line was just hanging there allowing more fumes in the boot and even in the car on hot days.

It took me some time to figure this out and I even had the tank redone as I thought there was a leak, but after the repair, the problem continued until I got rid of the vented cap and increased the size of the vent and its line.
This all happened before this forum or even the internet.

 

Hey Jeff, yeah, makes sense to get the vent hose as far away as possible from the middle of the car.

...and I do remember seeing the dia. of the vent, and thinking it was pretty small.

Thanks!

 

Chris
I use aftermarket facet type pumps in my MK1 and MK2. They are both 2.4 cars which have been fitted with HD6 (13/4 inch) SU carbies.
The pressure from these can be too high and lead to flooding.
Consequently, I use fuel pressure regulators set to 2 PSI after the pumps.
I did experiment around different pressure settings and found 3 psi was getting a bit marginal on the flooding issue. (Occasional flooding)

 

Facet pumps are excellent. I use Hardi Pumps which make the right noise & can't be seen. They are direct fit ~ No mods required. Used by Porsche until EFI. This is on 3.8 XK engine.