MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB Technical - mgb non starter

have just bought a 1973 mgb gt which had been dry stored for a number of years.i gave her a service and added some fuel but could not get her started.the batteries are fine and the engine turns over.i have a spark.
after removing the air filters i squirted some fuel into the air intake and she fired up but only ran for a couple of secs.when i squirt fuel into the air intake she starts and then i block off the intake with my hand she revs high.take my hand away and she cuts out.
any one got any ideas as it is driving me crazy.
g askew

As you discovered, your engine is seemingly not getting the fuel it needs. The reason it started when you added fuel manually is due to the fact that the fuel your added burned and more fuel was not supplied. You have to trouble shoot why you are not getting fuel. Can you hear your fuel pump working? Besides the noise, another way to check this is to pull the gas line off of the float bowl on your carb and place the end into a jar and see if your pump fills it with fuel. I usually find that it is best to try simple solutions first. Such as: maybe a hose clamp has cut the rubber fuel line and it is sucking in air near the carb, etc. try to examine all rubber fuel line connections (at carbs also at fuel filters) If your fuel lines look dry it is best to replace them anyways. Try to trouble shoot these problems outside. -Jeremy
jeremy

sorry jeremy forgot to say i have got fuel at the float chambers.
g askew

You may have old varnishy fuel in the carburator assemblies depending on how long the car was stored.
Check the carb needle asemblies from the fuel bowls and the needle valves at the bowls.

Was the car running correctly before storage? Did someone fiddle w/ the carb adjustments?
Luigi

what i fail to understand is,why,by blocking off an air intake she will only rev high.take my hand away and she stops.
g askew

If she holds the rev, then shes getting gas. It sounds like you may have an open vacume line. Check all the hoses to the intake and replace any that are cracked or broken.

Luigi
Luigi

The craziest thing that ever happened to me was that the welch plug on the cowl side of my intake manifold popped off. I had myself and two very bright and English car experienced engineers baffled on the roadside. We would dump fuel in, and the car would catch, but then that extra lean condition would just take over. So - Luigi may well be on to something.

While the float bowls are full at the moment - is fuel pumping? I've had to prime the fuel pump a few times on stored MG's.
John Z

good point.iwill check first thing in morning.if there was a leak would there be much suction at the air intake?i have got quite a lot.
g askew

"Much" isn't an exact measure. An IC engine is an air pump by definition - so if you have a *small* leak in a vacuum line or elsewhere, I imagine you'd still feel vacuum.

BTW - When you say you say the car runs at high revs with the intake blocked, that sounds compatible with an air leak - high revs typically are due to a lean condition, and if the intake is blocked - where's the air coming from???
John Z

Wildly out of kilter carbs and ignition could also be the cause if the car hasn't run for a number of years ... the exception to this would be if you put it away and it was working then. As a purchaser of effectively a non-runner there could be any number of things wrong, including missing and incorrect parts. Check for the missing inlet manifold Welch plug by all means as it only takes a moment, but after that I'd set up valves, plugs, points, timing and carbs (in that order) from first principles replacing any manky stuff including cap, rotor and leads as a matter of course. If you are new to setting up twin SUs you are going to need some help, it isn't difficlut but things must be done properly and in the correct order or you will be wasting your time, you can't poke and hope with them. You can read how to set up ignition and carbs at http://www.mgb-stuff.org.uk/ then click on 'Spanners' and 'Ignition', then 'Fuel' and 'SU Carbs'. Other web sites are available.
Paul Hunt 2

John Z,
I had the same thing once, but in my case, the plug only fell halfway out. If you could coax the engine speed up and let the throttle close quickly, it would suck the plug back in and all was well. Then a bump or something with the throttle open and low vacuum would let the plug fall open again. Since the car would not idle with the plug open, it was really hard to diagnose. It would only start with full choke, and of course there was a tendency to snap the throttle open and closed when starting this way. This would suck the plug back in, and with the plug in it was perfect. This went on for several weeks of random failures.
FRM
FR Millmore

excuse my ignorance guys,what and where is the welch plug?
g askew

Welch or core plug, used to block holes from casting/machining. There are two in the manifold balance pipe between carbs, one at each end. About 1" diameter.
FRM
FR Millmore

FYI - The one application for welch plugs that everyone is familiar with are "freeze" plugs in the block.

As FRM states, they are on either end of the intake manifold "log". Naturally, the one that popped off for me was the one towards the driver, and was invisible.

Apparently designed by the same engineer who ensures that wipers first develop a streak on the driver's side, at eye level.
John Z

John Z,
Of course, the rear plug is the only one that ever comes loose. This is becuz the acceleration of the car forces the front one tighter, but loosens the rear one! And the wiper smear is due to the action of lookie rays through the glass impinging on the wiper rubbers, usually much greater on driver side. All perfectly ordinary engineering principles.
FRM
FR Millmore

This thread was discussed between 18/10/2005 and 20/10/2005

MG MGB Technical index

This thread is from the archive. The Live MG MGB Technical BBS is active now.