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MG MGB Technical - Fuel starvation up hills

My 70GT (twin SUs) has developed a new problem. Maybe something to do with her passing her 156000 mile birthday.

When I drive hard up hill I think I start starving for fuel. The car starts spluttering. Back off the throttle and she'll recover. I need to do a few more experiments but I am sure it is something to do with not enough fuel going to the carbs when going uphills. It is especially bad if I floor it just before the hill.

This is a worry since I live in Auckland and have to drive over the harbour bridge to get to work. It's one big hill and not the place to conk out!

The car doesn't have an SU fuel pump but rather a little square box type. Seems to be working OK normally. I have a fairly new fuel tank (few months old) and I did fit a filter which I will check when I get home. I am thinking of parking on a hill when I go home and seeing if I can make it happen stationary to get a better idea of what's going on.

Is there anything else I can test out? Any suggestions?

Simon
Simon Jansen

Simon,

Just curious -- did this starvation problem begin after replacing the fuel tank?

Does it happen with a full tank?

Could you be sucking in a bit of air in the connections from the tank to the pump?

Just some thoughts.....
glg

Sorry, forgot to say I do have a full tank of fuel. The problem only started occuring last week. Before that she has been fine. Had the new tank on for months with no signs of trouble. The new tank isn't baffled but since it is full I am sure it is not a pick up problem.

I will check out the fuel lines and the filter and around the pump to see if air could be leaking in somewhere.

Thanks.

Simon
Simon Jansen

Simon,

OK. You might want to check the carb pistons for bits of dirt/grime that might be hanging up their free movement.

Does the present problem resemble low oil level in the carbs? And just another thought, check any air/vacum hoses eg: distributor advance and anything else off your intake manifold.
glg

Simon. You may wish to check to see that the tank has a good vent. I have also seen this problem with fuel pump lines were clogged or twisted. You might also want to remove the fuel line at the pump outlet and the carb and blow some compressed air through it from the carb end to flush out any crud which may be in it. I do not see how the steep angle could affect the ability of the floats to open and allow fuel into the carb, but it might be worth pulling the lids and inspecting them anyway. Sputtering and coughting with loss of power could also be ignition related. What does the tach do when this happens? King lead (coil lead) insulation breaking down and, on a slope, grounding out? Carefully check all of the leads in a dark gargage with the engine running. Keep the garage door open, if possible and keep hands away from the spinning parts. Les
Les Bengtson

How about fuel quality? Water in the system can cause interesting "events".
Doug
D Sjostrom

Simon,

I mention the carb and vacum lines in the context of an over-all trouble shooting -- if there is something there that is just begining to go wrong, eg: dirty carb pistons, it would show up early, when putting a load on the enginge -- asking it to do things like go up a hill.

I'm sure you'll find this is some small problem to fix, which is one of the beauties of owning a simple motor car.

Post your progress.


glg
glg

Simon,

I recently this problem myself driving up the New England highway in Australia. Driving up a long steep incline, the motor died and yet after coasting to a halt I could start and drive away OK. The key hint was the fuel pump still ticking as I coasted to a halt. Even with a full tank, I experienced the same problem on the same hill twice that trip. Could the pump be underpowered? or not getting enough voltage? My auto electrician and I have checked both these out and can't find any reason.

However check the tank vent is venting and changing the filter may help.

Let us know if you solve the problem.

Dirk

71MGB
Dirk Richards

Doug may have a good idea about water in the gas. If the car sits out overnight regularly, especially in high humidity, you can collect water condensate from the atmosphere eventually.

With a recent tank replacement, and if the car is garaged, that my not be likely, but getting a slug of water and crap from a bad lot of contaminated fuel from an old in ground storage tank can do it for you all at one blow, explaining the sudden appearance of this problem. Since the water tends to pool on the bottom of the tank, you would think that it should show up sputtering and coughing and losing power on the level with the fuel pipe in the tank sucking from the lowest point. But if your pickup pipe is not quite where it belongs or the fuel and water move to the pickup as you go up hill, then you could suck some up.

Also, as mentioned, check for air leaks in the fuel line. If you have hoses joining the fuel pipes, they sometimes crack all the way through along their length and this can appear to the suction side of the fuel pump like a broken straw does when we try to take in some soda.
Bob Muenchausen

Sounds like you are runnig out of gas.A good way to check this is to find a spot on the road where you can control the malfuntion without getting hit by another car/truck. The drill is easy, once the car starts spluttering turn the key off and coast to the side of the road take the tops off the float bowls if its a fuel delivery problem one or both bowls will empty or close to it.Assumeing you find low/no fuel your next step is to check your pump for pressure and volume, if not you might want to check your ignition.RIC
R E L Lloyd

Driving home tonight it suddenly occurred to me it is probably nothing to do with uphill. That's just when I do have my foot to the floor usually! Putting a load on it as GLG suggests. I could try revving it for a bit standing still and see if eventually it splutters. I am starting to suspect the filter I put in when I put in the new tank .Won't be able to look properly until the weekend.

Thanks for all the suggestions!

Simon
Simon Jansen

Simon,

I had a similar problem 20 years ago.

It turned out that the pipe from the tank to the pump had become slightly porous due to rust. When the fuel pump had to suck particularly hard going up hill it was drawing air in through the rust.

You should get a quick idea of the state of the pipe from the tank to the pump by looking under the car.

David
David Witham

Well, here's my two cents worth...

First I've had a similar problem with water in the gas. The car ran okay until it was under a 'load' and then it missed badly! (not an MG)

On my '74 MG I was having a missing problem a couple of years ago going up big hills. Turned out to be that the points were shorting out. Ran okay until it was under a load. Point is, don't rule out the electrical possibilities.

Good luck!
Jim

Jim Budrow

Had a similar problem on mine about 2 weeks ago.
It just wouldn't accelerate at all well. This was most marked when going up hill while accelerating. It would splutter just like it was starving for fuel as you mentioned. I though it was to do with the hole in my exahaust that still needs fixing.

It turned out the timing had got itself well out of tune. The points gap had closed up and the timing had slipped. When all this was reset it was like driving a different car. Its worth checkig and reseting the timing and then maybe move onto the carbs and possible vacuum advance leaks when this is set.
andrew.horrocks

Simon

To further the melee of answers, my recent *uphill* fuel starvation problems were caused by a holed solid fuel line above the axle and a knackered original fuel pump - car currently also at 150,000 as yours. the fuel pump had been *slow* for sometime but with the holed fuel line it just couldnt suck the fuel through quick enough.

Before you get too fruity with the carb settings if the car is otherwise running fine, i would check that the fuel is getting from the tank properly first.

In the archives is the rate at idele and load which the fuel pump should deliver. Check that before fiddling with carbs IMO too!

GL

~PHIL
Phil

Revving it standing still probably won't do much good, driving it in 4th on the flat with the brakes on will be a better test of load as an alternative to incline. An SU pump should deliver at least 1 imperial pint per minute, check yours is delivering at least that by disconnecting a pipe at the carb and directing it into a container. Seeing as how you have an aftermarket pump do you have a pressure restrictor as well? Another possibility.
Paul Hunt

Simon: Hows that fuel filter you were going to check? Sounds like a classic case of dirt clogging the filter. I would adhere to the KISS principal in your diagnosis process and eliminate the easy things first.
Andrew Blackley

Andrew, I won't have time to check until the weekend but the filter is the first thing I will look at.

Simon
Simon Jansen

OK, just in case anyone who helped was wondering how I got on I pulled the fuel filter out and I think that maybe there was a leak in it. Hard to tell. It didn't seem blocked. I had another handy and have put that on. Just when I was going to go for a test drive up some nice hills I found my brake lights no longer worked. Didn't have time to check that out. Found this morning that it was a bad connection in the fuse block. Have no time right now for the test drive though. Oh, and these things must come in threes because I was winding the window up and the handle broke :)

Simon
Simon Jansen

OK, not the fuel filter. Replaced that and it still splutters. So much for a quick fix. Now all I need is the time to look into things properly! Lots of good suggestions here to try.

Simon
Simon Jansen

I was looking at the bently the other day and noticed something that made reminded me of this thread. I sure this has no merit but.....the mgb float hinges run perpendicular to the length of the car. When going uphill the fuel level in the rear float bowl would be higher near the hinge. Because of the arc of the travel of the float, this might simulate a higher fuel level and raise the float a little more than it should be, thus closing the needle valve too soon.

Then again....maybe not.
Fred H

Simon, I would check the bottom of the bowls in each carb for water or other foreign matter. It could be that when you are on level road the gasoline on top of the water is being burned with no problem. On an angle the water underneath the fuel covers the pick up hole and gets sucked into the fuel circuit. Good luck.
Dann Wade

Fuel level: FWIW I had occasion to run my V8 with the fuel pump on a manual switch for a short time, I found no difference at all in the way the engine ran until immediately before one or both carbs ran out altogether, i.e. it ran perfectly with the fuel pump switched off for half a minute or more at town speeds. Since spluttering on hills is not a common occurrence to all and sundry it cannot be float angle on its own, it has to be a defect.
Paul Hunt

My car has a manual fuel cut off as an anti theft device. I used to sometimes forget to turn it back on and the car would run a good half minute of so before spluttering. The spluttering then is just like I see now.

I just need the time to check it out fully. I am halfway through building little motorcycles and telescopes right now! Not enough hours in the day!
Simon Jansen

Bad Excuse there Simon --You down under folks are about mid-way into Spring and your day-light is getting longer.

Are YOU running out of fuel?!??
glg

Supposed to be spring but Auckland has had crappy weather all week. Had a tropical downpour yesterday! I tell you telescope building is damn frustrating when the weather is so bad you can't see the sky to look at anything!

I was out last night fuelling up on Old Speckled Hen!
Simon Jansen

Did your inability to see the sky come before or after the Old Speckled Hen Fest?
glg

Paul, I understand what you are saying about the level not being a typical problem, but what if the float level is out of adjustment? Might that be enough to cause the valve to close when on a hill, but run normally on the level?
Fred H

Fred - I really do doubt it. I've been up and down 1 in 3 hills without any hint of poor running in either orientation, and even if the float was so badly set that the float chamber was almost completely empty in normal running you would have to be even steeper than that before the jet pipe on one carb (and one carb only) was clear of fuel. I have had a fuel pump cut-off switch on the roadster as well and just like the V8 it runs normally until it runs out. However if the float were loose such that it could rest on the side of the chamber when on an incline and hence held the float valve closed you would get problems, but surely normal vibration would joggle the float down and the valve open.
Paul Hunt

OK, today in between the scope and bike building I had a chance to check out the car. I checked the fuel lines and they seemes a little loose around the carbs. I tightened all of the clips a little. I also checked the oil in the carb dashpots and found the front one was very low. I cleaned them out and put in fresh oil then went for a test drive. Between that and tightening the clips the problem seems to have gone! I will go for a drive tomorrow up a good hill on the motorway near here for a real test.

Simon
Simon Jansen

This thread was discussed between 17/11/2003 and 29/11/2003

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