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MG MGB Technical - Intermittent fuel delivery problem?

I think I have a fuel starvation problem that is driving me nuts. The car is a 1967 MGB-GT. When I first drive away when the car is cold, the engine sounds like it is running out of gas. When the car warms up after a few miles, everything is OK, but, on the highway, at 65mph or so, I get an intermittent fuel starvation problem again. The problems comes and goes, as if the float bowls aren't being filled fast enough.
Here is what I have done to the car recently:
1. New carbs, AUD 325 I think
2. Richer needles from Joe Curto, to correct a lean fuel condition from the K&N's
3. New fuel pump and filter
The car starts on the first try and will rev easily to 4000-4500 rpm when the problem is not there.
Can anyone offer any clues?
Thanks in advance,
Steve
Steve Brooks

The basic question: have you considered a fuel venting problem? If air can't get into the tank, fuel can't get out. Some people have a vented filler cap. Others have a vent system that leads to a canister in front of the right-side firewall. In either case, if the vent become totally/partially clogged, you will encounter the symptoms you mention.

Check the vents or take the filler cap off for a test drive and see if that has any effect on operations.
Dan

As fuel starvation is quite rare an airleak somewhere is much more likely and will produce the same symptoms. The intermittance may just be down to the warming up of the joints or the increased vacuum effect at high speed. I would instantly suspect something to do with the work you've just had done -especially the manifold seal around your new carbs. You would have to be very unlucky to get a problem like this after fitting new parts from something you hadn't changed I had a similar problem and after a lot of digging around found an air leak on the intake manifold.Get a can of WD40 and spray it on every join between the carb and the cylinder head if the WD40 is sucked into the fuel sytem at that point you will get smoke and a misfire - this will be the source of the air leak
Toby

Steve,
What is the condition/age of the fuel tank and lines? Rust and crud in an old tank and lines can cause the same type of problem. Does pulling out the choke help? Is there any debris in the float bowls? I have had a old rusty gas tank cause problems before.

HTH

Ron
Ron Smith

Ron...The gas tank was replaced with a new one from Moss 4 or 5 years ago. Fuel lines are original, even though this is an Arizona car, they could be corroded internally.
Toby...I will try your suggestion today and see what happens.
Thanks, all.
Steve
Steve Brooks

All of the above, and I would also check the floats and needle valves.

Any teeny, tiny, piece of loose debris having come from the new carb installation can hang things up.
A thorough backflushing with a blast of aerosol carb cleaner (the ones that come with a long, thin nozzle) and compressed air usually gets rid of the junk. Wear goggles while doing this. I would also
remove the rubber fuel lines (especially the ones downriver from the fuel filter) and flush them, too.

While you have things apart - check the float level. Since they are new carbs, the float level might
have not been set to factory specs. It wouldn't hurt to check and confirm this. The Robert Bentley
manual (The Complete MGB) outlines this simple but important procedure.

Look down inside the fuel bowls, themselves. See any finely powdered orange-rust deposits in
there? If so, you gotta get it out. Swishing a parts pickup magnet in the fuel bowl will grab most of the
rust, but you'll still will have to drain out and clean the bowl in order to get all of it. Use the carb cleaner
spray to blast out any stubborn rust and flush the bowl fuel feed hoses.

If there was any rust in the float bowls, chances are that some of it may have worked it way into the carb
needles. Remove the dashpots and pistons and blast out the needle orifice with carb cleaner. Check
the float bowls, again, to see if any junk was flushed in there and remove them.
Daniel Wong

You might want to make sure that your fuel pump is grounded properly. I had a problem with my fuel pump on my 67 roadster cutting in and out while going down the road. Turned out to be a loose connection on it's ground wire. The fuel pump's ground wire (at least on my roadster) is terminated on one of the studs holding the rear licence plate on. Worth a check. -Rod
Rod in NC

I had similar problems with my 67GT. NOw cured! Multiple problems! The needles and seats in the float bowls were slightly worn, (cheap easy fix). I had an unvented fuel cap instead of a vented cap (they look the same)
I replaced the fuel filter
and the condensor on the distributor (cheap and easy)
Oh, and I topped up the dampers on the dashpots.
Good luck....

Brad French

If the hoses on your car are old, sometimes they can crack along their length, the crack actually going all the way through! In this circumstance, the vacuum applied by the fuel pump will suck air as well as fuel. It is the same as when you have broken a soda straw and it leaks. This doesn't happen often, but sometimes a hose closest to the tank (if there is one there on your car) can cause this. Also, loose steel fuel line connections anywhere between the tank and pump can also behave like the broken straw and suck air. FWIW.
Bob Muenchausen

Steve, I've had the same problem for the last year or so -- never have found a remedy, though. I've gone through everything I can think of, and the advice of some of the knowledgable posters on this site. In my situation, I was able to eliminate fuel supply starvation from the equation by running the car on a long uphill gind on the interstate until the starvation symptoms began. At this point I immediately shifted to neutral, shut off the engine and electrics completely, hit the four way flashers, and coasted to the side of the road (with a generous shoulder). I immediately removed the float bowl covers to find a healthy supply of fuel present in each. Back at home, I also found that mixture adjustment was impossible to equalize -- the front carburetor would invariaby run lean (this with airflow balanced with the Unisyn). I've run the car for about a year now taking care to keep below 65 on the interstate. What a pain. Possibly a little more diagnostic will help pinpointwhat exactly is wrong -- I have found fuel and ignition problems to be discouragingly hard to distinguish at times...

Best of luck

Mike
Mike Lord

Mike. Have you checked you floats to see if they may have fuel inside them?
I'm wiating for a big brown truck to deliver me a pair of floats. I've had
trouble trying to balance the carbs since I boughts my 68 GT six months ago.
I got around to looking at the floats last week and the front float was about 1/3 full
of fuel. Clifton
Clifton Gordon

Thanks everyone for the input on my situation!
Mike Lord, Even though there are no real hills here in Phoenix, I do remember last year on run up north, I was waiting in traffic on a steep hill and when I went to move ahead, I had zero power, and just made it to the top of the grade. Once at the top and the car was level, everything was OK. But, this was before I bought new carbs.
Bob M. I will check for leaks and cracks on the steel fuel lines and check all threaded fuel line connections.
Steve
Steve Brooks

A corroded connection, broken wire, dirty ground clamp --- to the fuel pump?
Dan

This thread was discussed between 05/01/2002 and 08/01/2002

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