Why does my MGA suddenly run so poorly?

I recently got the car out of many years of hibernation and registered it. It took more work to start than it used to but it ran fairly well, and I put 100 or so miles on it driving to work and dinner and such, it was nice to have it back after being mothballed for 10 years.

Now, suddenly, it runs like ass. I can't figure out why. Here are more details:

1960 MGA, basically stock including twin 1.5" SU carbs
Before it was mothballed it had a full workover including carb rebuild and adjustment and ignition part replacement and adjustment by guys in the local MG club where I lived then who had beards, wear tweed, and drink beer with sticks and mud in it (so they must know what they are doing), after that it ran wonderfully. Since then it probably only has 300 miles on it.

Recently when I revived it, it was running well, but idling quite high and feeling a wee bit down on power aside from the previously mentioned difficulty starting, overall it was driveable just fine. One night when I got home and it was still warm, I adjusted the idle, made a very small adjustment to sync the carbs, and adjusted the mixture a bit on the rear carb. The next time I tried to drive it I barely got it started, and it ran like total crap, no power, sputtering, not running on all 4, and then barely able to stay running at all.

Since that day I put the carb mixture back where it was before, made sure the fuel pump is working, made sure there was fuel in both float bowls and cleaned the float level jets, took off the throttle dampers and cleaned everything out (it looked good in there), adjusted point gap, tried alternate ignition coil and rotor and cap, checked that it is getting spark at the plugs, cleaned the plugs, adjusted the valves, looked for any other potential vacuum leaks, and nothing at all has made a change.

I'm basically out of ideas. The car still runs like ass and is un driveable. Tonight I was able to get it to idle OK, but give it any throttle and it hesitates, sputters, and has lots of trouble. I've tried every combo of choke on and off and partial, nothing makes it better. It was so nice to have the car back and useful, I'm super bummed to have it now being a bitch. I'm almost ready to just megasquirt it, but that would take away from other projects that are more important, like building my locost or a spare motor for the lemons car, or renovate my kitchen.

I'd run some carb cleaner through the various jets and other orifices of the SUs first, in case you have crud from evaporating gas in there.

When a car sits that long it can build up sediment that quickly fills the fuel filter. I have also found that it settles in fuel lines and can stop them up. You said you had fuel in the bowls. Disconnect the incoming fuel line and hold so that it can flow fuel into a container. Then have someone turn on the ignition and see how much fuel actually flows over a given time.

Thanks for the replies so far, here are some answers

I've sprayed a bit of carb cleaner down the jet holes when I had the pistons out, nothing else though.

I have looked briefly for vac leaks and not seen them, but I'll double check. I agree on most carb issues being electrical, hence why I tried alternate ignition parts as part of my troubleshooting

There are 2 fuel filters in line, the one in the engine bay is clear, with no visible sediment. When I pull the line off, it flows out pretty quickly and without sediment in the container. Over the years I have drained the gas from the tank a few times and had stabil in there with it.

I'll poke around with it a bit more tomorrow, I'm just hoping for a solution that is easier than pulling the carbs for a full going through.

Did you muck with the filters? If so, did you assemble properly so the hole is not blocked on the front face of the carb?

Try a gravity feed fuel supply to the carbs. That will qualify or disqualify the fuel system.

How old is the fuel in the carbs? If its a year old, its junk. Stabil sucks.

The lines in the jet might be clogged with crap. These are the flex lines that run from the float bowl to the jet under the carb body. If they gum up, they can restrict flow.

Have you had a peek inside the float bowl?

When ever I have an issue, I sart with the basics, compression test, electrical tune up and timing set to 12 BTDC or whatever the manual says. Set the valves to 0.015" cold and you should be good.

If you have a timing light, you can clip it on to each plug wire to see if it is missing; the miss shows up quite well.

I was going to suggest fuel filter as well. My MGA would run great until I would drive at a higher speed, then intermittently, it would lose power, idle too high, and generally run bad. I would stop the car check distributor, plug wires. My fuel filter was nice and clear and full of fuel. I finally figured it out by leaving the engine on when it happened and within a few minutes, it cleared up and ran great again. It was a combination of a aged fuel pump and a partially blocked filter. Of course, while inspecting the plugs and bores prior to that discovery, I saw what looked like a cracked piston. I pulled the head and found it cracked, a burned valve, and evidence of a long-ago blown head gasket. I raced this particular car (it's been in GRM a few times!) and retired it, but it ran great with all the hidden damage. It has an 1822cc 'B engine now. After the install, I found the bad filter. It looked ok, but clogged. Comparing the new clean filter, it was pretty obvious.

So it could be a fuel filter or you might need a new engine.

Ha, I hope it's not new engine time, this one was recently rebuilt mileage wise, as was the fuel pump. It's easy enough to replace the filters though, just to be sure, but the fuel flow was good when I let the pump run with the line into a cup.

Air filters have been off for a while now. The car had a full tank of fresh fuel put it when I got it back on the road. I have blown out the fuel supply lines between the filter and the carb float bowls, and there was no gunk in the float bowls.

Good idea on the timing light to check spark pulse is regular, I'll try that.

Yes, there is oil in the dashpots, at the right level. I'm not sure if the carb pistons rise when revving, I'll have to check. I just checked and the one and only vacuum line is connected. When I was playing with the pistons, they aren't dropping down in the bore all that quickly, so the jet may not be centered...

Its getting a hot white-blue spark at the plugs?

have you checked the ground side of the ignition primary circuit?

Generally, when I Berkley with my SU carbs... And then it runs like E36 M3, it's because I Berkleyed with the carbs. I suggest you go un-Berkley them.

My success with SU tuning went way up once I invested in a glass spark plug so I could see the color of the 'splosion and an actual carb sync tool that shows the amount of air passing through each carb. It's pretty easy to set up one of these cars so that 70% of the air passes through one carb. Then Berkley with the mixture in the wrong way on the 'good' carb and car will barely run.

Fresh gas is a good idea but I've run several of mine on 2 and 3 year old gas without issue

If you think it is carburator SETTING related, here is how you get back to where you need to be.

1-Set the floats. Do not do it as the book suggest. Rather, remove the "bell" from the top of the carb and set it aside with the piston. Now pull the choke linkage so that the jet is at the bottom of its travel. Now you can muck about with the float level; the goal is to have the fuel just over the top of the jet when it is in the lowered position. For reasons I wont get into, doint this by the book does not often give the desired result.

2-Release the choke. Now, turning the nut under the carb, bring the jet up until it is flush with the "bridge". Once it is flush, turn it back down 12 flats or two turns.

Assuming there is nothing damaged or worn too bad, this will put you damn near to where you need to be. If the engine wont run reasonably well with this set-up, then look elsewhere for the problem.

Balancing the carbs:

With the car warmed up and the choke off. Slacken the linkage so that the two carbs are not connected. Now holding a hose to each carb intake, listen to the hiss. when they sound the same, tighten the linkage.

Hillbilly carb balance: slacken the linkage. screw the throttle screws out on both carbs. tighten the linkage. Use the throttle screw on one carb and bring the idle up to what you want. Leave the other alone since it is slaved to the other carb.

Since no one has mentioned it: Check the timing. Maybe the distributor has wandered.

Maybe a weak coil!? Check the spark as mentioned. Obviously, if you have a spare coil (the are pretty generic back then), swapping it out is the easiest.

Check the ignition....... the rubbing block for the points may have suffered after sitting for so long... get a dwell meter and see if you have 60 degrees of dwell (+ or - 3 degrees)

NOHOME wrote: Balancing the carbs: With the car warmed up and the choke off. Slacken the linkage so that the two carbs are not connected. Now holding a hose to each carb intake, listen to the hiss. when they sound the same, tighten the linkage.

Doing this ^ is exactly how I ended up with 70% of the air going through one SU carb. Maybe your ears are better calibrated than mine.

LuxInterior wrote:

NOHOME wrote: Balancing the carbs: With the car warmed up and the choke off. Slacken the linkage so that the two carbs are not connected. Now holding a hose to each carb intake, listen to the hiss. when they sound the same, tighten the linkage.

Doing this ^ is exactly how I ended up with 70% of the air going through one SU carb. Maybe your ears are better calibrated than mine.

That funny because I actually did a comparison between the Unisyn balance tool and the piece of aquarium tube method. 3 individuals manages to get damn near the same results using either tool.

The hillbilly method also works fine if you are not looking for perfection.

If you have 70% of the air going through one carb, you will be able to see that the one piston is up further than the other. You should be able to get them close just by adjusting until they are the same.

The other myth that the manual perpetuates is the one where you lift the piston 1/8" and listen for a rise and fall in rpm to tell you the mix is perfect. In some perfect world that might work, but not in the one where my MGs exist.

Lots of great feedback, thanks!

Here's what I've done yesterday and today and the current status:

I took off the carbs, took apart the jets and made sure they were cleaned and lubricated, centered the jets, set the float bowl levels, and set the jet heights at level with the bridge minus 2 turns to get it even and baseline.

After all of that, it wasn't any better at all. Still awful, couldn't even get it to idle. With the carbs set where they should work, I turned my attention to the ignition system. I confirmed my spark plug wires were on in the correct order (1-3-4-2 CCW). I've changed the rotor and cap/wires to spares, no change. I tried an alternate coil, no difference. I triple checked the points gap, and cleaned them with a nail file, the points look new (which they basically are). The distributor is firmly bolted down, and looks to be about where it has been as long as I've had the car, so I don't think it wandered.

Nothing. Now it won't even sputter to life at all.

So, more checking: I pulled a plug and held it to the block, the spark seems weak and yellow with either coil. I put a timing light on the plug wires, and at first it would occasionally blink, but eventually it wasn't blinking at all.

I even tried spraying carb cleaner (no ether on hand) right down the throat of the carbs with the butterflies open while cranking, no fire at all. I don't have a dwell meter to check it, but without the car even running at all, can I even check the dwell?

After all this, its clear this is a spark issue, not a carb issue. Forget adjusting the carbs, the car doesn't even really run. The only thing I haven't replaced is the condenser, so I'm hoping one of the FLAPS will have one of those. I was really trying to get the car ready for my town's annual car show, as this is when it was finally running.

Aside from replacing the condenser (and replacing the plugs with good ol' Champions or NGKs for good measure), any other suggestions?

AngryP: you mentioned ground of the ignition primary circuit, how do I check that?

Condenser failure will just cause the points to wear rapidly IIRC. Verify all your connections, especially the grounding. I had a very similar problem on a car once, coil died and then it wouldn't run at all after changing it. Turns out the whole ignition system grounded through one of the rusty bolts holding the coil down, I disturbed it changing the coil and poof, crappy spark.

Kenny_McCormic wrote: Verify all your connections, especially the grounding. I had a very similar problem on a car once, coil died and then it wouldn't run at all after changing it. Turns out the whole ignition system grounded through one of the rusty bolts holding the coil down, I disturbed it changing the coil and poof, crappy spark.

Also check that the wire for the points, or condenser is not grounding to the dist case/housing

To check dwell on a car that doesn't run... remove all the spark plugs, attach dwell meter, crank engine... with all the plugs out the dwell should be pretty close/reliable.

if I remember correctly ... a condenser is an automotive name for a capacitor ... and yes they can go bad

when I had points cars, I remember being told ... "never do a tune up without changing the condenser along with the coil and the points"

In reply to wbjones:

Coils are good till they aren't, points/condenser should always be changed together, and preferably set with a dwell meter.

Wow, condenser - there's a term from a long-gone era. But I'll bet that's your culprit.

So where is any of the ignition system supposed to ground? The Distributor grounds to the block I would imagine, and the - terminal on the coil goes to the spade on the side of the distributor which connects to the wires inside. What else is there?

Yep, I say condenser as well. I had one of those things

whip.

my.

ass.

for about 2 weeks on a Hodaka motorcycle. Had a blue spark, the timing and compression were both on the money, the carb was fresh and after being apart 3 or 4 more times was even fresherer. I tried pull starting, it sounded like it wanted to run but just would not. The weird thing was the cylinder head got warm, though.

I finally took the flywheel off for about the umptyleventh time to check the points, I looked at the condenser and said dammit I might as well change it. Dug in my junk box, found one approximately the same size etc but of unknown parentage, stuck it in and put the flywheel back on.

I poked the kickstarter sorta halfassedly, before it made half its travel the thing fired up and idled just as happy as a clam.

Sonic wrote: So where is any of the ignition system supposed to ground? The Distributor grounds to the block I would imagine, and the - terminal on the coil goes to the spade on the side of the distributor which connects to the wires inside. What else is there?

the points make/break the ground side of the circuit, so you need integrity from the ground terminal on the coil to the points, through the point plate's connection to the distributor, through the distributor to the block, through the block to the chassis, and from the chassis to the ground terminal on the battery.

after googling "what does an ignition condenser do", i feel dumber for having read so many conflicting answers and / or just flat out wrong descriptions of ignition components.

When my Spitfire started running real crappy, it turned out it was the points. So I changed them (not filed) and the condenser. It was like new car. And the old points only had a few thousands miles, more likely several hundred, from new. I aslo bought a relatively expensive set of points from NAPA instead of Lucas points.