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MG MGA - Need Help with a strange problem

I am seeking the combined wisdom of the BBS. My car (1959 1500 roadster) was running perfectly as I took it on a high speed run for about 60 km. with no problem. Two days ago I refilled the tank with gas and now I cannot drive for more than about 1/2 mile before the car stumbles badly to the point where it will completely die. If I wait a minute or two it will start up and then run as normal for a short time.I did switch off the last time this happened and opened both float bowls, expecting to find no fuel, but they were both full.
So I figured fuel starvation maybe due to crud in a 50 year old tank. I removed the fuel filter in the pump and it had no sign of debris. I also blew the fuel pump intake line back with compressed air. I have installed a fuel filter on the firewall before the carbs and it does not look dirty. I would appreciate any ideas you may have.
Regards,
Tom
Tom Heath

It has been said that most fuel problems are electrical related! Your symptoms could be caused by a condenser failure - easy to change over. Good luck!
Cam Cunningham

Disconnect fuel hose from heater shelf to rear carb. Place hose end in a catch vessel, switch on, and observe fuel flow. If you get a gusher, at least one pint per minute, it's not a fuel delivery problem.

Float champers are full and no run, check for spark at the spark plug connectors. Otherwise perhaps water in that new tank of fuel. Open the float chamber and transfer the fuel inside into a clear glass. Fuel will float on top of water. Enough water will separate and go to bottom of float chamber, and the engine will not run on water.

Another possibility, if fuel and spark but no run, the rubber grommets on the banjo bolt mounting the float chamber may be deteriorated and clogging the holes in the banjo bolt.
Barney Gaylord

My coil rubbed against the mount and leaked oil once. It would run fine but as the coil heated up it would crap out and quit.

After a few minutes the coil would cool down and the engine would start again. In a few minutes the coil would heat up again from the lack of oil and the process would repeat. My first thought was a fuel restiction. I blew my fuel lines and cleaned the fuel pump prior to discovering this.

The earlier MGAs have the coil bolted to the top of the generator and if on too tight the mount can eventually wear through the outer metal layer of the coil. I use a bit of inner tube between the coil mount and coil now.

Good luck.
Bill Haglan

Tom. Since the problem is consistent and easily repeatable, hook up a dwell/tach to the coil terminal going to the distributor and run a jumper lead back to the passenger compartment. Either use an assistant or position the tach where it may be easily seen when driving. Take the car out until the engine shows problems and examine the tach. If it drops to zero as the engine dies, it is a low tension ignition circuit problem. If it winds down as the engine is slowing, it is a fuel system or high tension ignition system problem.

Les
Les Bengtson

Bill is likely to have I.D.ed the cause. Also check wires at the fuse-box.
David Werblow

It does sound exactly like my re current fuel problem where a thin wafer of clear silicone sealant was floating about in the fuel filter ( an aftermarket glass in-line type fitted near the fuel tank).
The silicone was invisible in the filter and I only found it when I dismantled the filter to double check it.
The silicone wafer rested on the bottom of the filter until I started the engine and then as fuel was pumped through, it floated with the flow and progressively covered the outlet of the filter.

The symptoms were that 1st the engine began to run on 3 cylinders, then on 2, then on one and then would cut out completely.

Then as when I switched the engine off for a couple of minutes, the pump would stop and the silicone would conveniently float back down to the bottom of the filter and unblock the outlet pipe.

This problem took me months to solve when I first got my car 4 years ago and I vowed to check the filter regularly after that.
Well I didnt keep my promise as the problem came back on a 300 mile run back from Scotland last month.
I found that if I kept my speed below 40mph I could keep the engine running and crawl back home.

It was really embarrassing to be overtaken by EVERYTHING on the A1, caravans, trucks, old ladies in Morris 1000s, a Ford Model T and even on one uphill section- a cyclist!!! I felt like I was a mobile roadblock and I was even mentioned on the traffic news on a North Country Local Radio!

I am going to check the filter every year from now on!

So I would do as Barney suggested and first check the fuel flow with the pump running.

Best of luck

Colyn
Colyn Firth

Thanks to all for your suggestions. I will start with checking the fuel flow (easy) and if that isn't the problem will turn to the electrics. I have a Pertronics unit in the distributor and the coil is mounted on the generator. It gets very hot!
Tom Heath

If you want to avoid a clogged fuel filter, remove it from the car.

MGA did not originally have a fuel filter, and should not need one. There is a screen in the fuel pump inlet, and also screens in the float chamber inlets. These screens should catch any debris large enough to clog a float valve or a main jet. Otherwise SU Carburetors are very tolerant of a substantial amount of dirt in the fuel system. Anything small enough to pass through the screens will also flow right through the carburetor without problem.

If you have enough junk in the fuel tank to clog a screen, then you need to clean the fuel tank. Starting with a clean tank and clean fuel, if you drive the car regularly the fuel flow will constantly cleans the whole fuel system, and you will never have a clogged filter.

If you don't drive the car much, or store the car for several months with half a tank of fuel, then it can eventually get rust in the tank. Either of these habits is a case of bad maintenance ($.02). If you insist on doing this, then a fuel filter may be a temporary alternative to periodically cleaning the tank. Never install a filter between the tank and an SU fuel pump (install it downstream from the pump). Some aftermarket pumps recommend a filter before the pump.

If you install a filter that will catch debris smaller than the screen openings, then you can throw out the screens downstream from the filter (or leave them in place with no harm). The filter will then catch smaller debris that would otherwise not affect the carburetors. This increases maintenance, requiring more frequent filter service (cleaning or replacement). Larger filter requires less frequent service. It also clogs up more gradually, so when it first gives signs of problems (bad running at high speed) you have more running time at higher speed before it gets much worse (less likely to cause traffic problems, and more likely to get you home).

When your filter clogs up more frequently than you like to service it, then it's time to clean the tank. Certain kinds of debris will clog up the works regardless of filter or no filter. Large enough junk in the tank can clog the entrance to the fuel pickup tube. Never use RTV sealant anywhere in the fuel system, as it can flake off inside to clog things up. Bare cork gaskets should seal the fuel sender unit. Thick paper gasket works for float covers or serviceable filters with no sealant required.
Barney Gaylord

Tom,

I had this problem about 25 years ago. My car would idle and rev when sitting with no problem. I would start to drive and within a short distance it would die. Start right up and idle great. The wire to the distributor frolm to coil had become loose. At idle the connection was fine. Hit a bump in the road and the connection would be lost.
M Gannon

Tom, I had exactly this problem with my BGT..discovered that a piece of rubber from the fuel filler cap had dropped into the tank, and instead of floating on top of the petrol, somehow sank to the bottom of the tank, and was being sucked onto the bottom of the fuel intank line. As soon as the ignition was turned off, the pump would stop, and the rubber was released until it got sucked in again!
After saying this though, I don't know if your problem is the same, as you say you had full fuel bowls?
Gary Lock

Soon as I read the first post,thought sounds just like water in the tank.Been there,had it.Can you drain off the tank and start again( from a different petrol station)? Good luck.
M Blencowe

Tom, I had a similar problem & after doing the usual checks the problem was identified as being in the distributor (I also have petronix electronic points)& a couple of mechanics said the unit needed replacing. I replaced the rotor first after reading some MGA forum threads and that was the faulty part costing a few minutes & a couple of dollars instead of a couple of hundred.
I Hazeldine

I also immediately thought water in the gas after reading the first post. Could be something electrical only failing when hot, but awfully coincidental that it happened right after a fill up.
Jeff Schultz

Jeff, My A was running nicley when I pulled into a shopping centre car park for only about 10 minutes. When I started the car the engine ran roughly so I gave it some choke & hoped it would settle down after a few km's, It didn't instead stalling & refusing to start until it had cooled down. It was summer so maybe heat soak aggravated the problem but it was eventually isolated & solved after another couple of break downs.
I Hazeldine

Thanks for your suggestions. So far I have tested the fuel flow as suggested by Barney and the pump seems to produce a good flow. I removed the fuel filter I had installed on the firewall. Also replaced the rubber washers between the float chambers and carburetors since I had a spare set. The problem actually seems to have become worse because the engine died while I was stationary. I am next going to look at the electrical side. My Lucas sport coil has a significant gouge in the case, but doesn't seem to be leaking. I will replace it and the distributor rotor as well.
I am wondering how tight the bolts holding the float bowl to the carb body should be. There seems to be a lot of give and the float chambers will rotate easily unless the bolts are drawn up quite tightly, but perhaps that distorts the rubber sealing washers? Any thoughts?
Thanks,
Tom
Tom Heath

There are metal and fiber washers that surround the float bowl rubber. The bottom dished metal washer needs to have the concave side up, IIRC...there was a thread on this recently.

See part 89 here. My car also had the washer shown as 92 - though I have a banjo bolt vs. the "stud and nut".

http://www.mossmotors.com/Shop/ViewProducts.aspx?PlateIndexID=29218

JIM in NH
AJ Mail

Tom, you say the coil gets very hot. This could be due to a short in the coil giving a high current, so worth checking/replacing. Or is the coil getting hot because the generator is overheating. This could be due to the regulator playing up causing the generator to stay on full charge, over-heating the generator and wrecking the battery too! The ignition could be packing-up when the coil overheats.
The condenser can also start to fail when it gets hot. Replace this and the points to eliminate this possibility.
Good luck.
Pete
P N Tipping

Tom,

I would put my money on a dead coil. I have had two Lucas sport coils die in the past three years. The first one leaked and suddenly failed. The second just a couple of months ago went kaput at the top of White Pass (4,000 feet). It did not appear to have leaked, but I could hear the coolant sloshing around. Fortunately I had a spare.

A noticeable indication that the coils were failing was a very slight hesitation at speed. As the second coil got worse I was getting some unburned fuel in the exhaust that sounded like I ran over some metal on the road when it ignited. My supposition is that the sport coil has little tolerance for a poorly performing ignition system. In my case the coil wire was in bad shape and probably causing the coil to overheat. Since replacing the ignition and coil wires and installing a pertronix epoxy filled coil, all problems disappeared.

As mentioned earlier, try only one fix at a time. The initial check of the coil can be done right on the car, see Barney’s site, http://www.mgaguru.com/mgtech/ignition/ig108.htm .

John

jbackman

Thanks to all - I believe it is the coil for when I removed it and could inspect it in daylight it was apparent that the case had a deep enough gouge that it had been leaking gradually. I believe that the clamping strap around the generator at one time worked loose so that the coil rotated down to where it could rub against the vibrating engine. I re-positioned the assembly when I saw this but the full damage was not obvious until I took the coil off. Mindful of others' experience with sport coils I have replaced with a standard coil and she fired right up and ran steadily in the garage - road test tomorrow.
Since the problem started after a fillup with fuel I of course suspected that as the most likely source of the problem. Another example of the meaning of "assume" as well as further support for the adage about 90% of fuel problems being electrical!
Tom Heath

Tom,
If you feel like a drive in the country, give me a call and plan a short trip to South Surrey. Good test for a new coil.
I've had one fail after 40 years. Now they last about 3 years on average! Last one died last year while we were parked overnight at Harrison Hot Springs. Fortunately I had a spare in the boot.
Peter.
P. Tilbury

This thread was discussed between 03/09/2011 and 09/09/2011

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