Fuel Bubbling in Tank No power.

Technical questions and answers
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Parker
Posts: 11
Joined: Fri Nov 21, 2014 5:48 am
Location: Camden Australia

Fuel Bubbling in Tank No power.

Post by Parker »

Long time since my last post.
When I turn on the ignition the fuel pump runs continually (as it probably should) but you can hear fuel in the petrol tank bubbling as the pump is sucking.
The engine has been completely rebuilt, new cam, rebore, pistons, rings, crank reground, new timing chain and gears, new oil pump etc etc.
Problem is it runs like a dog. It starts fine and idles smoothly and quietly, but as soon as you accelerate the engine dies. You can get it mobile but it has no power and dies at every gear change and then finally gets some revs and dies on the next rear change. It has no power up hills and dies even when changing down a gear.
I have taken it to a Land Rover expert and left it there for 2 months to play with but he couldn't get it going properly.
He checked: valve timing, coil, distributor, vacuum and carbies.
The carbies have had new kits put in them and cleaned but we suspect they may be quite worn.
It has a new pump but it works no better than the old one. He did a fuel flow test and said it was OK. I have looked for air leaks but there are no signs.
When I asked how much I owe he said "nothing as I couldn't fix it but now have no hair left".
Any ideas?
Graham

1980 Stage 1
2014 RRS HSE SD V8
1952 Bentley Mk VI
1955 Daimler Century
1971 MG Midget
1971 Norton Commando
1972 Norton Commando
map1275
Posts: 1076
Joined: Mon Jul 21, 2008 2:48 am
Location: Brisbane, Australia

Re: Fuel Bubbling in Tank No power.

Post by map1275 »

If it's 'bubbling' in the tank then you have the pump lines connected back to front. Fittings on the pump are the same thread. It is just as likely that the tank has been converted from non-return item and the return pipe doesn't run to the bottom of the tank, creating splash. You can view pick-up and return through the sender hole. Delivery and return lines should be a different diameter, 5/16 and 1/4.

I assume you haven't created a vacuum in the tank or in the float bowls and that cam timing is correct.
Last edited by map1275 on Wed Sep 27, 2017 6:52 am, edited 1 time in total.
disco2hse
Posts: 1637
Joined: Sun Apr 27, 2008 3:51 am
Location: Auckland NZ

Re: Fuel Bubbling in Tank No power.

Post by disco2hse »

If the pipes were the wrong way around, then surely you would have no start because there would be no fuel getting to the carbs. Is what the OP hearing bubbling or just the return pipe fuel re-entering the tank? Also, is the fuel line crimped somewhere, and have you checked and cleaned the fuel filters?

What you describe reflects a lack of power, which may be due to fuel leakage after the fuel pump or vacuum leakage between the tank and the fuel pump. Otherwise these are other issues that may be implicated:
- Poor compression (if compression is very low then is will be rings and/or valves, otherwise blown head gasket between cylinders)
- Badly seated valves, or the wrong valves
- faulty muffler, block exhaust
- Incorrect timing (I would check this first)
- Faulty spark plugs, or wrong ones
- Faulty coil, condenser, or battery
- Air inlet blocked
Alan

1983 ex-army FFR 109 Stage 1
2005 Disco 2 HSE TD5
map1275
Posts: 1076
Joined: Mon Jul 21, 2008 2:48 am
Location: Brisbane, Australia

Re: Fuel Bubbling in Tank No power.

Post by map1275 »

With a constant fuel return system there's no one way valve at the float bowl exit. Potentially allowing the bowls to be back filled through the return pipe. This would require a proper return pip inside the tank which almost reaches as low as the pickup tube.

I have managed to block the pickup strainer on scale filled tanks. The filter inside the pump is also frequently missed. Though rare, a blocked silencer is frequently missed and the cause of much hair pulling. More often a hard start issue. But as the first box has a flange joint at each end, you only have to take off the three bolts and run noisy. The power difference, if present, will be instantly noticeable. The hydraulic tappets can also hide worn cam lobes. But as usual, start with the basic settings.
disco2hse
Posts: 1637
Joined: Sun Apr 27, 2008 3:51 am
Location: Auckland NZ

Re: Fuel Bubbling in Tank No power.

Post by disco2hse »

Good thinking about the pump. I hadn't thought of that. It wouldn't happen on mine because I have a different system, with two relays (one for pump switching and one for return flow) controlling the flow between front and rear tanks via the two pumps but only one return pipe that is separated at the relay.

I thought about the cam (that affected me), but as the OP said it was fully rebuilt, I assumed the cam would be new. Possibly not?

The strainers were what I had in mind, plus the main filter under the air filter.
Alan

1983 ex-army FFR 109 Stage 1
2005 Disco 2 HSE TD5
Parker
Posts: 11
Joined: Fri Nov 21, 2014 5:48 am
Location: Camden Australia

Re: Fuel Bubbling in Tank No power.

Post by Parker »

Thanks for the responses.
It is a new cam and lifters. The heads were reconditioned and it has 130 lbs compression on each cylinder and the timing has been checked both valve and vacuum.
So I have ruled out mechanical problems.
Its a new pump and new filters all round. I have checked them again and not a bit of dirt. It did have a filthy fuel tank originally as it had been sitting for 10 years. Before I cleaned the tank it went just OK but would block the filters after a short drive so that's when I removed the tank and treated it with POR and everything is now clean. I checked the fuel flow yesterday at both the delivery and return and it is flowing strongly. Could there be a blockage in the carbs that blocks fuel just above idle as it seems like fuel is bypassing the carbs and going straight back to the tank? I would love to try a different set of carbies as I am convinced I have missed something in cleaning the old ones. I am pulling them off today and going through the cleaning more thoroughly.

One other confusing thing which may be related. ON my vacuum/ advance there are two pipes, one out of the top going to the left carb and another underneath with no hose off it. Please see attached photo.
Again thanks for all the ideas.
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Graham

1980 Stage 1
2014 RRS HSE SD V8
1952 Bentley Mk VI
1955 Daimler Century
1971 MG Midget
1971 Norton Commando
1972 Norton Commando
disco2hse
Posts: 1637
Joined: Sun Apr 27, 2008 3:51 am
Location: Auckland NZ

Re: Fuel Bubbling in Tank No power.

Post by disco2hse »

Could there be a blockage in the carbs that blocks fuel just above idle as it seems like fuel is bypassing the carbs and going straight back to the tank?
Yes, and the carbs may not have been set/tuned correctly, incorrect needles, ... The vacuum tube is not split I take it.

Does start to point back to fuel supply and electrics. A sideways view of the dizzy might be more useful.

Have you ensured that the vacuum advance is even working on the dizzy? Have run with the vacuum pipe disengaged (it should actually do what you have described in that case).

From page 86-25
The distributor incorporates two automatic ignition advance mechanisms-a vacuum-controlled unit related to carburetter choke depression and a centrifugally-controlled unit related to engine speed. Both units are connected to the contact breaker assembly, and operate independently, progressively moving tbe contact breaker through a small arc about the cam.

A loss of engine performance, particularly a sudden loss could be due to a malfunction of either of the automatic advance mechanisms and where suitable electronic engine tuning and equipment is available, both units can be checked against the figures detailed in Section 05-Engine Tuning Data.

The test should commence at maximum advance conditions and be checked during deceleration.
Alan

1983 ex-army FFR 109 Stage 1
2005 Disco 2 HSE TD5
Parker
Posts: 11
Joined: Fri Nov 21, 2014 5:48 am
Location: Camden Australia

Re: Fuel Bubbling in Tank No power.

Post by Parker »

Hi Alan
The Vacuum line is good with no leaks. The LR mechanic checked the distributor and said the advance was working as it should. The bloke I bought the car from said it had been running good before it blew a valley gasket and that was why he parked it for 10 years!
So I have rebuilt everything except for complete overhaul of the carbs. I think that is my problem. Would love to find a good set or better still NOS.
Graham

1980 Stage 1
2014 RRS HSE SD V8
1952 Bentley Mk VI
1955 Daimler Century
1971 MG Midget
1971 Norton Commando
1972 Norton Commando
disco2hse
Posts: 1637
Joined: Sun Apr 27, 2008 3:51 am
Location: Auckland NZ

Re: Fuel Bubbling in Tank No power.

Post by disco2hse »

OK. Another thought that occurred to me is a leak on the inlet manifold. I had that problem on a six cylinder Austin truck many years ago. It would cause the engine to sputter and die as soon as you put your foot on the accelerator. I assume too that you have checked the fuel mix and that it is not too lean?
Alan

1983 ex-army FFR 109 Stage 1
2005 Disco 2 HSE TD5
map1275
Posts: 1076
Joined: Mon Jul 21, 2008 2:48 am
Location: Brisbane, Australia

Re: Fuel Bubbling in Tank No power.

Post by map1275 »

So your distributor has vacuum advance and retard. Is it the correct distributor for the application and working properly?
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