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MG Midget and Sprite Technical - Passed MOT Yesterday & Now Won't Run!

Hi All,

My midget passed it's first MOT in 10 years yesterday, after 6 or so months of tinkering.
It initially failed emissions, but I adjusted the jets up about 1.5 flats and got through with CO of about 2.5%
That said it did seem slightly lean (rpm dropped when carb pistons lifted).
Upon arriving back at my lock-up I noticed a growing puddle of liquid under the car, turned out to be fuel.
It looked like it was coming out the overflow, so I put the car away for the night, planning to tackle it in the morning, and have my first proper drive in the car.
I disassembled the floats, but all was fine, and restarted the car, turned out the rubber link on the pipe that feeds the front carb was worn out.
Replaced this, and the other rubber pipes around the carb, and now I cannot get the car to run properly!
It occasionally starts, stumbles and rumbles around, and then stalls.
The floats are both full, and none of the pipes seem to be blocked, so I am not sure that these things are related.
I have had trouble with flooding it recently, not really sure of the proper use of choke in warm weather (but when the car is cold), I played with it a bit but couldn't seem to get it any better.
Pulling a plug showed them to be quite sooty, so I gave them all a clean.
I have no idea what is going on, so was hoping one of you may have some advice.
I have put a video of it starting, just, and then running a bit and stalling on YouTube if it helps:

Thanks in advance, hopefully I can fix it soon, really looking forward to a drive!
-- Josh
J Levine

The black smoke indicates far too much fuel is being taken in by the engine.
Is the choke control on the dash free to move and allow the jets under the carbs to return fully (up) when released?
The coke must be fully in when the engine is warm, don't try to start it with the choke pulled out when it is warm or it will exhibit the symptoms your video shows.
JB Anderson

Thanks for the rapid response!
The choke control is free to move, and as far as I could feel/see, the jets return all the way.
The engine was at ambient temperature, so "cold".
Any thoughts on what may be going on?

-- Josh
J Levine

Yep first things first Josh

Make sure the choke lever is allowing the jets (bottom of carbs) to return fully up the centre. Many times these tend to stick and the choke stays on.

Equally you maybe adjusted the mixture at the MOT centre when the chokes were sticking on, it would be best now to start again from scratch with the mixture set up.
Robert (Bob) Midget Turbo

It sounds just like my brother's MGB did when I went round there yesterday evening.

It was running on two cylinders and smoking. I found that the jet tube on the rear carb was not returning when the choke was pushed in. As I had a couple of spare spark plugs with me, I changed plugs 3 & 4.

Tried again and still running on two. Pulled off number 1 then number 2 plug difference. Refitted the plugs that I had removed into 1 & 2 and it ran fine. Bizarre!
Dave O'Neill 2

Josh, The problem may have solved itself overnight with the evaporation of any excess fuel, in which case it should start normally with choke initially.

It it is still behaving as in the video I would take the aircleaner off and have a good look at the jets under the carbs and make sure they are working properly when the choke is operated.

If they are working normally, and returning fully when the choke is pushed in then, as Robert says, I would start from scratch and follow the full carb. set-up procedure as found in manuals.

It is definitely a fuel/carb. problem (obviously!)
JB Anderson

Thanks for the advice, I think the approach suggested by JB makes sense, and I will get started later today.
As someone who has never really lived with a carb fed car before, could someone explain what should be done when stopping a car that hasn't yet warmed up yet?
I seem to have problems like this, when I start the car (with choke) and the stop it, without letting it warm, or putting the choke back in.
I am guessing that I end up delivering loads of fuel into the cylinders...

-- Josh
J Levine

There's also the chance that one of your float valves isn't sealing properly, and is allowing the float chamber to overfill. This will cause an extremely rich mix, hence the sooty plugs.

Best of luck!

Gryf Ketcherside

Josh, the more you drive the car the more you'll learn how to set things and read it's dials and where it's fluid levels like to be

for carbs see the links I'll put in following post

obviously if the car is not fully and properly serviced and maintained then it's starting and running will be compromised

the owners Handbook will give you a great deal of guidance

(ref: 0058) -

as for the MOT well done on getting a pass but bear in mind that it means the car passed a minimum standard to one person's judgement at that particular time on that particular day, MOT doesn't mean the car is in good condition, fully and properly serviced or effecient - things wear and brake and malfunction all the time so need checking and attention regularly
Nigel Atkins

these will give you the principals of the carbs

part 1 of 2
Nigel Atkins

part 2 of 2
Nigel Atkins

If you switch off an engine still running on choke it should not be a problem, but excess fuel will no doubt have got into the engine which could cause a restart difficulty.
I would say you would probably not need to pull the choke out fully on the restart (depending on how long it was running for prior to switch off) but you just have to try and see.
Always use the least choke possible, to avoid flooding the engine but usually on the first start full choke should be required very briefly and then it should be pushed in gradually, until warm.

If the engine becomes flooded with fuel then push the accelerator pedal to the floor and keep it there, without pumping it, while you turn the engine over on the starter.(Make sure the choke is fully returned to the "off" position.)
This opens the butterfly valves in the carbs which lets plenty of air into the engine to counteract the excess fuel, and eventually the engine should fire up.

You may then have to "catch it" by using the choke, and keep it running until warm with a bit of judicious choke manipulation.
JB Anderson

Hi All,

Not having much luck with this, any further help would be much appreciated.

This is what I have done today:
- Disassembled and cleaned the floats and pistons of the carbs.
- The jets wouldn't wind to the bridge (presumably this is the cast aluminium bit that crosses the carb, rather then the brass bearing)?
- One did seem to wind slightly higher, but I ignored it as I am not sure how to deal with it (short of breaking out the vernier calipers).
- Wound them as high as they would go, and 12 flats back.

The car behaves exactly as before.
Won't start with or without choke, occasionally catches enough to disengage the starter, but doesn't start, once or twice started briefly, and stumbled to a stall.
Plugs sooty (as expected if started on choke?), but I did give them a clean, and leave them out a while to evaporate excess fuel in the cylinders.

I should reiterate, that the only thing I changed, from it working, to not working, was a few fuel hoses.
The floats are full, so there isn't a delivery problem, and the valves are working just fine.

The battery is now on to charge, overdid it with all the cranking.

-- Josh
J Levine

Oh, one more thought.
When I turned it over, with the dizzy cap off, I noticed some slight arching between the points, that normal?
I tested the spark and it seemed weaker then normal (orange rather then white/blue).
Failed condenser might explain the points, and the spark.
Then again, could have been the low battery (~12v).

-- Josh
J Levine

A little sparking across the points is normal, Particularly when cranking a ballast ignition system (higher current while cranking).
This could well turn out being an electrical fault but lets not jump ahead just yet. Recheck the strength of the spark with a recharged battery and report back.
Also could you confirm which Carb jets are fitted eg wax or standard? As you've got the car in a nice warm garage (well compared to one up here!), try starting it without choke. If it is set up rich or flooding you might have more luck. When you had the carb's stripped did you check the float needle valves are closing properly? It has been known for flooding to occur via the jet instead of the overflow! So just in case the valves are not sealing, remove the dash pots again and check for fuel being pumped out of the jet whilst cranking.
After that we are possibly looking at electrical issues. First I would eliminate the ballast resistor by running a wire from the coil +ve directly to a permanent live eg to the battery or the brown wires on the fuse box but don't leave it on for long if it does start running as you'll burn the coil out. Then try a different coil, condenser etc.

M McAndrew

Battery is freshly charged, so I am off for another attempt.
The jets are waxstat.
I will try without choke first, and see how it goes.
Float needles are fine, and working as they should, will check for fuel pumping anyway.
And do a full electrical check.

-- Josh
J Levine

Definitely an electrical problem.

I replaced the condenser with an older one, and it started right up, ran for about 10 minutes (waiting for it to warm so I could fix the carbs), and promptly died!

Tried fiddling with the condenser and points to no real avail, managed to get it to run once, but it was all over the place, tach dancing around.

Suggestions on where to start with this?
I am an Electrical & Electronic Engineer, so this is supposed to be the easy stuff!
Had a probe with a continuity meter, and there are no obvious problems.
I will take the condensers to work on Tuesday and see if they at least are correct at room temp.

-- Josh
J Levine

So am I and a similar fault had me scratching my head for a while....
The tach bouncing around is symptomatic of a LT problem. Could be earth faults as the car has not been used for a while. Check continuity from engine to body, body to battery, dissy to engine and from dissy body to the points mounting plate.
Did you try a new coil feed wire from +12 to the coil +ve after it stopped? Can you get your hands on a standard 12v non ballast coil? Fit this with a new feed as described previously to eliminate the Ballast resistor and ignition switch. The ballast resistor is actually a resistive wire running from the ignition sw along the loom under the dash and is joined to a standard wire which then goes to the coil. The resistive wires do fail with strange symptoms and I would rule this out before moving on.

Best of luck.

M McAndrew

My money is on the electrical integrity/conductivity of the points mounting plate to dist. body. And/or condensor. (Never a good idea to replace electrical components with old/unknown components). But you've probably disturbed the baseplate connection to dist. body resulting in an intermittent good connection.

But none of this explains the coincidence that your fault materialised immediately after you changed your fuel hoses.

Andy Hock

Continuity all seemed good when I tested it, but think I will disassemble, clean and reassemble.
Tried a different coil (still ballasted) and it was similar.
Fed coil directly and again, no difference.
I will check the resistance wire anyway!

-- Josh
J Levine


different coil with original wiring?
direct wiring with original coil?
or other combo's?

It is possible to have more than one fault!

As Andy says none of this explains a coincidence with the fuel hoses and I don't really belief in coincidence! On that point did you fit new fuel hoses at the pump? Is it possible you have disturbed some wiring in that area eg the connections on the starter solenoid or to the dissy. Be safe, check and clean them all.

M McAndrew

Fair point Mike!
Tomorrow I will try all the combinations, so far it was:

- Existing wiring + other coil
- Existing coil + hot wired

Something has come to mind though, when I checked for continuity between the condenser/points (with the points open) and GND, I was surprised to find around 12ohms.
I would have expected none.
When removing the connection to the coil it was 0ohms again.
My car has a suppressor for the radio, wondering if it may have failed (closed circuit)...
This would connect the +ve side of the coil to GND.

-- Josh
J Levine

>>JL wrote>>when I checked for continuity between the condenser/points (with the points open) and GND, I was surprised to find around 12ohms

>>AH replies>>One side of the points is bolted to the distributor baseplate which should be held to ground by the tiny flying lead and the dist' body, IIRC.

The other side of the points is electrically connected to one side of the coil. The other side of the coil is connected to the +12v feed from the solenoid (also via the ballast resistor/lead for starting). Also connected to the coil is the tacho pulse feed (on the points side of the coil IIRC). And, you say you have a supressor connected, too.

It's many years since I worked on any'points/condensor' configuration, but I can't account for your 12ohms reading. Thinking out loud, with the points open, one side should read zero ohms to ground. With the ignition key 'off', the other side should read, at the very least, a few megohms (the circuit resistance of the tachometer pulse input pin).

12ohms does suggest either your condensor or supressor has gone resistive. But, I could be wrong. As I say, it's been years since I worked on any points system.

Andy Hock

Time for an update I think.
Unfortunately I didn't have any luck fixing things on the long weekend.
I tried all combinations of wiring+coil.
I tested the condensers at work, and one of them is definably gone, the other seemed to have a lower capacitance then expected (around 0.20uF), but it seems like there is some conflicting information over what it should be (around 20uF or 0.20uF!).
I think that the 12ohms was a path through the coil, the coil power line and a bulb in the car, as the suppressor seems to be fine!
I have ordered replacement points and condensers, and will have another bash at diagnosing when I get the chance.

-- Josh
J Levine

Er - I suppose you have the plug leads on the right firing order?
Chris H (1970 Midget 1275)

Hi Chris,

I think so, but the thought did occur to me!
1-3-4-2 with 3 by the vacuum chamber.

-- Josh
J Levine

1342 I assume you know that is ANTICLOCKWISE on the dissy when viewed from above.
Robert (Bob) Midget Turbo

Pleased to say that new condenser fixed it!
I am fairly confident that it was the condenser, as I was very thorough in my earlier tinkering.
Had my first ever proper drive just now, and it runs beautifully.
Just need to sort out the carbs which I messed up at the beginning of this game!

Thanks for all the assistance,
-- A very happy Midget owner
J Levine

This thread was discussed between 21/05/2011 and 02/06/2011

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