OK I have tried almost everything to solve a problem that has come up on my 1968 3.4 S type but now hit a wall apart from a couple of further thing I will look at tomorrow (listed at the bottom) but any advice or suggestions would be appreciated.
Problem.
I was having a bit of a lumpy engine, almost felt like it was not firing on all cylinders under load and at speed. Tick over was fine. Started to work on the car yesterday and she started up straight away ran for 30 seconds and then stopped on me. Would not start again and the battery drained. Battery put on charge over night. This morning she started ran for 10 seconds and stopped. Would not start again. Can't remember which fuel tank was switched on.
My attempts at a solution.
Last year I had a set of carbs professionally cleaned and rebuilt which I fitted and the engine had been running on these just fine up until recently when the problem started.
New alternator fitted only last year.
Checked for a spark on all cylinders and changed the plugs for new. HT leads are silicon and only a couple of years old but I swapped them around with a spare set I had but no change.
Fitted a new coil, no change.
Electronic ignition in the Dizzy which has been checked and shown to be working fine.
Fuel pumps both checked and fuel getting to the fuel bowl although one fuel pump appears weaker than the other. Will come to that later.
Pulled the float bowl lids and both contained fuel at the right level.
So four hours later after the battery had been charging, turned the key and she started straight away. Ran for 30 mins and got nice and warm. At this time she was running on the right hand tank. Swapped over to the left tank and within a minute the engine died and would not start again. I turned back to the right hand tank thinking a fuel pump issue but she would still not start. Battery ran out of juice again trying to start her so put the tools away and will wait for the morning again.
So the fuel pumps. The right hand tank has an original SU with points. Initially ticks away to fill the float bowls and works fine. Left hand tank has an original SU that has been converted to an electronic setup ( not by me) so no points. Does not tick but you can hear and feel the diaphragm banging away when you first turn it on. This is the one I described as feeling weak. To rule out a vacuum stopping the fuel from drawing the filler caps were both removed. Only a couple of weeks ago I filled both tanks with fresh fuel so it not a case of stale fuel in the tank.
Still to do.
In the morning I will release the fuel lines on the fuel pump out lines to make sure that the pumps are pulling fuel from the tanks and sending it up to the engine although I am pretty sure this is the case as the glass filter bowl is full and there is fuel in the float bowls. I have ordered a new fuel filter for the glass bowl but I have also tried running it without the filter in just in case it was blocked. I still have the old SU carbs in the garage so when I was checking the fuel levels in the float bowls I swapped the float bowl lids over for the original ones along with the float valves.
My mate Steve came to have a look and decided to blow down the fuel line on the left tank and rather than create bubbles in the tank he just pressurised the fuel in the pipe and when he tried remove the pipe from his mouth he got the contents of the pipe thrown all over him. (I did laugh). I don't think this should have happened so my concern is the left tank might be a cause. Either a blocked internal filter or ????? I am running out of guesses but I will have to pull the plug on the bottom of the tank and check the gauze filter. Just don't know where to put the 6 gallons of fuel that are in the tank at the moment that I know will come out of the plug at the bottom.
Any suggestions in the meantime would be greatly appreciated.

 

Could be a plugged filter in the tank. I'm wondering if there is some water in the bottom of the left tank and that's why the car stops running soon after selecting that tank? Other thought is the disk valves in the right pump are not seating correctly, so the left pump is pumping to the right tank, instead of to the carbs?

You can get a 30L pail at B&Q for £7, that might be a temporary place to put the fuel while you siphon it out of the tank? I'd probably siphon most of the fuel out and put it in a safe place, then put a tray under the tank and drain the last gallon or so from the drain plug, and then you can see if there is any contamination.

I'd replace the drain plug gasket once you've removed the plug, I've had trouble getting them to seal again once disturbed. Same with the glass bowl filter seal. Tank gasket part number is C26310, glass bowl sealing ring is 7298.

 

Have the tanks been treated with an internal sealer? Pieces can fall off and cause intermittent blockage of an in-tank filter, the fuel pipe, or pump inlet. Rust and dirt can do the same thing, though not quite as effectively.

I know I always mention it, but it baffled my Dad and me for several months. Check there are no small leaks from the top hose on to the distributor.

 

About 5 years ago I treated both tanks when I replaced them with POR15 so that is what I will check for tomorrow. Thanks for the suggestion. Unlikely to be water as the tanks are well sealed and out of direct water spray but there might have been water in a tank of fuel I have bought so will check for that as well.
​​​​​​​When I remove the feed pipes tomorrow I will run the pumps and see where the fuel flow is going. Once done I will report back.

 

I've been down this road. With fuel in float chambers & filter & the car won't run.

What is your fuel pressure? ~ should be around 3psi minimum, but not much higher than that or you sink the floats.

The other cause of trouble is a rust hole in the pick up tube that goes down inside the tank into the stone catcher/ahem filter. Then the car runs fine on one tank sometimes but not the other. However if the hole is big enough in the one tank pickup the whole system goes down.

Measure your constant fuel pressure to the carbs, preferably with the engine running but if it won't run the check is still valid.

We might have 2 pumps but there is no valving in the lines.

Also check the breather system on both tanks. Removal of both fuel caps is a good start. The caps are not vented if you have genuine ones. The replacements are vented but incorrect so I restored my originals. With vented caps there is a constant smell of fuel at the rear.

I presume both tanks have fuel in them. You are far too smart to make that sort of error.

 

As I have already stated Glyn both tanks were filled last week so plenty of fuel which then creates the problem of having to find somewhere to store the fuel in the tank whilst I strip it out and check it. Don't have a 7 gallon can lying around and both tanks on the car are almost full. Having said that I have spare fuel tanks in the garage so might be able to syphon off the fuel in to a spare if I can find the brass plug and a fresh seal for it.
I mentioned several weeks ago that I was having what I thought was an SU fuel pump failure on one tank but when checked it proved not to be the pump. That fault seem to come and go and now it has come and stayed so I think you guys are right that it is possibly fuel tank related rather than fuel pump, engine electronics or carb problems as I have done everything I can to eliminate those.
So today I will try and empty the left tank and take a look inside.

 

I'll almost put the family jewels on you having an air leak on at least one pick up pipe or a blocked breather. You are lucky you have spare tanks. I had 6 tanks. 3 LHS & 3 RHS. We picked the ones that looked the best and the others ended up crushed. Now I have a LHS tank that wont drain completely. Fixing that pickup pipe is a sod. It's built as part of the tank. So it is degas & cut it out. My first restorer that I fired "lost" my fully coated inside & out tanks (More likely sold them to someone because they looked as new)

Also check all feed pipes but I'm sure you have done that as drips/air leaks in the boot or on the floor are so easily detected.

I envy your nice lift set up. Ideal to sit on a chair & work on the tanks.

 

So yesterday I started to drain the left tank but before completing that I disconnected the output line from the left SU fuel pump and switched it on and the pump merrily pumped half a pint of fuel up the pipe into a container for me. So rather than drain the tank I started the engine on the right tank and it functioned perfectly. I then turned it on to the left tank and it ran but I could tell it was not running as smoothly as it had been on the right tank. A couple of splutters and at one point tried to die on me. Clicked it back to the right tank and it went back to running smoothly.
So I am waiting for some parts from SNG then over the weekend I will drain the left tank completely and try to have a look inside.
The left pump is the electronically converted pump so it might even be that this pump is not producing enough PSI but I have no way of checking this. I would have thought as long as fuel is being pumped to the SU float chambers the PSI should not matter as minimal pressure and gravity would open the float needle to allow fuel in. I did not monitor the fuel level in the glass bowl but I have ordered a new fuel filter element and will check this when I put the new filter in.

 

Yes ~ that was my logic too but I was proven wrong.

 

OK to continue this saga. I have been out and done some driving using the fuel in the right tank so I was able to syphon some of the fuel in the left tank and dump it in the right tank over the last week. Today I knew I only had about eight to ten litres left in the left tank so rather than syphon it out of the filler I went in and disconnected the fuel line from the fuel pump to the carb and put this into a fuel container. I then started up the pump and sent the fuel into the container. Filled one container and dumped this into the right tank. Whilst filling the container for the second time I decided to release the pump from its mounts so I could get to the fuel pipe from the tank to the pump. As I moved the fuel pipe the amount of fuel being pumped into the container doubled in volume. A bit of a eureka moment as I could see that the rubber fuel pipe from the tank to the pump had collapsed slightly on one of the bends which was restricting the amount of fuel being let through.
Superb I had actually found a fault.
Anyway with the tank now completely empty I removed the big brass plug on the bottom and pulled the gauze filter out. Filter was clean and there was no debris that I could feel around the base of the tank. I fitted a long piece of fuel hose to the tank outlet at the top and put my finger over the pipe at the bottom and blew and I was able to completely seal this pipe so there is not an issue with an air hole causing a problem with pickup. Having cleaned the gauze filter and re sealed the brass plug with a new seal (the old one was already cracking up when I removed it). I then replaced both lengths of fuel pipe running to and from the fuel pump and made sure that the pipes had enough length and room not to kink up again.
I am hoping this has solved the problem in that the kink and collapsing pipe was just restricting the amount of fuel being able to flow to the carbs. Later I will have a run out to the fuel station and put some fuel in the left tank, check for leaks and see if the problem has been solved.

 

i would devise tests such that each one removes half of the possibilities. i.e. ...might think of gravity feeding the carb(s) as the first test.

 

The joy of an S Type. Two tanks so if I know it is running off one tank correctly it must be the other tank that is at fault. Breaking that tank down there is the fuel pump which has been tested and working correctly. Debris in the tank with a blockage which has been checked and is ok. A blocked or collapsed fuel pipe or in my case a kink in the pipe which has been found and fixed.
Still not been out to put fuel in yet but will let you know what happens.

 

Today I popped out and put a couple of gallons of fuel in the left tank. When I got home I checked for leaks and primed the left system. Started the car and she runs as she should on both tanks so I am confident that the problem was the kinked fuel hose caused possibly by E10 softening the hose (supposed to be E10 compatible) to a point where it collapsed on a bend from the tank to the pump. This restricted the amount of fuel flow to the engine and could not keep up with the demand from the engine which is why it was cutting out.
New fuel hose fitted on the left tank and I think I will swap out the fuel hose on the right tank just to be sure I don't get the same problem again.

 

SU Carbs seem very pressure sensitive. It's not merely a matter of having fuel there in the float bowls & glass filter.

 

The kink was between the tank and the pump? Not downstream of the pump? I could certainly see that causing problems. Glad you were able to solve it reasonably easily.

 

Yes there is a small fuel rubber hose coming from the top of the tank to the fuel pump which is sat in the rear wing behind the light cluster which is over the top of the fuel tank for those without an S Type. This rubber hose was slightly longer than required and went up slightly higher than the fuel pump inlet then curved down to join it. The rubber hose had become soft (not leaking) and the inside of the curve had folded in on itself restricting the flow. When I was doing all my checks previously I had not noticed it as firstly when I disconnected the fuel pump outlet I was getting fuel. Secondly I then removed the pump from its cubby hole and the rubber hose straightened so all looked fine. It was only when I decided to drain the final litre of fuel from the tank using the fuel pump that I noticed an increase in flow as I removed the pump from its cubby hole whilst the pump was pumping fuel into a fuel can. If I had not removed the fuel pump thereby straightening the rubber hose whilst it was pumping I possibly would still be no wiser now.

 

Is it a classic example of British "cut to fit"? It relies on the care, skill and experience of the mechanical fitter to cut a piece of rubber tube such that it isn't stretched or kinked. Or is it an example of how even the best rubber doesn't resist fuel anything like as well as genuine nylon?