MG stalling hot

[Dave Sherman]

My '77 Midget is giving me some grief lately. A couple of times now, it gets to operating temperature, and then it refuses to stay idling. Tooling along the road is fine, although when it was being particularly bad about it, it would stumble a little at speed. It's getting a bit frustrating sitting at a light and having to keep goosing the throttle to keep it running.

Vapor lock might be the culprit, but years ago it had a bad vapor lock problem because the mechanical fuel pump would get hot enough to boil the gas. This was a problem even when it was new; I believe in '79 they got a redesigned fuel pump that had a thick spacer to help insulate it from the heat of the engine block. I have bypassed the mechanical pump entirely and installed an electric fuel pump at the tank.

I'm wondering if it's the same issue it usually has if it's hot and I park it for a while. It seems like it builds up heat under to hood, and it won't stay idling until I start moving. I'm sure building up hot air under the hood does not help driveability much.

 

[BigCahuna]

Back in the day that was a real PITA with older cars. A few low cost do it yourself cures you can try are, wrap the gas line closest to the heat source with aluminum foil, or rubber heater hose. Alot depends on how close the gas line runs to the motor. If all else fails, you can try re -routing the gas line under the hood with new line. ,,,

 

[NitroM3]

Howdy Dave...
Love the MG's never owned a Midget but owned several TD's TF's MGA and MGB's.
You read would need a list of Q&A to try to narrow it down.

I had a few issues with vapor lock and also added a electrical fuel pump. But as you say it just started ... my first thought is to pull the carb and to a cleaning. If that is to much then as soon as the next time it happens shut off the engine and remove a spark plug and have a look at how it is burning. Take a good HD picture and post it.


Good thinking Big!!!

 

[Vercingetorix]

 

[Vercingetorix]

Howdy Dave...
Love the MG's never owned a Midget but owned several TD's TF's MGA and MGB's.
You read would need a list of Q&A to try to narrow it down.

I had a few issues with vapor lock and also added a electrical fuel pump. But as you say it just started ... my first thought is to pull the carb and to a cleaning. If that is to much then as soon as the next time it happens shut off the engine and remove a spark plug and have a look at how it is burning. Take a good HD picture and post it.


Good thinking Big!!!

Seriously, I would look for an ethanol free gas station.

 

[JeffKeryk]

Fuel delivery is usually worse under load than at idle. If your ignition system is up to snuff, my guess is something in the carb idle circuit....
My brother had a bugeye Sprite. Love to have that one today...
Good luck.

 

[ctrcbob]

Can’t speak for the MG’s in the hot weather, however I had a lot of experience with my 1960 Triumph TR3A. I was living in Nicosia Cyprus (1960 & 1961). Summer temperatures were Hot HOT.
107F today, (110F tomorrow and Wednesday, 111F Thursday, all per Yahoo Weather). Neither my buddy who had the same car or I ever had Vapor Lock or Fuel Pump or Carburetor problems due to the HOT summer temperatures.
No car A/C back then.

P.S. Wish I was still that skinny.

 

[Wrenchturner44]

In the mid 70's British Leyland cars (MG, Triumph, Jags) were known for weak ignition coils when they got hot. See if you can swap a temporary coil and see if it is plagued with the same symptoms. You can also check the coil with an OHM meter to see if it is up to spec.

Check also the vacuum advance if the distributor has one to make sure it can hold vacuum. Some later MGs had a different kind of advance besides the vacuum one.

If you are still running points based ignition, you may want to consider swapping it out for one of these;

PerTronix D172429 Flame-Thrower Electronic Distributor Cast British 25D 4cyl Side Exit Plug and Play with Ignitor II Technology with Vacuum

Highlights All new lightweight cast aluminum housings. Tailored advance curve for optimal performance and drivability. Integrated Ignitor II electronic ignition with variable dwell maintains peak energy throughout the entire RPM range, reducing misfires while improving engine performance...

pertronixbrands.com

I too would check the internal cleanliness of the carbs as well as the possibility of internally collapsed rubber fuel lines.

We are seeing these on some older engines now that may not have had rubber fuel lines upgraded or changed in the last 10 years or so. This is due to the variances in ethanol fuel blends around the country.

Good Luck, Don't let the "Prince Of Darkness" defeat you and remember to keep your sense of humor.

Lucas - Prince of Darkness - Lucas Electrical Humor Jokes

www.mez.co.uk

 

[Trav]

Delete.

 

[atikovi]

I have bypassed the mechanical pump entirely and installed an electric fuel pump at the tank.

How old is it?

 

[Dave Sherman]

Thanks all for the suggestions. The fuel pump is a Facet cube, maybe 10 years old, but I've only put about 5,000 miles on it. It's also in back mounted to the bulkhead in front of the gas tank, so it's not in the hot engine compartment. I did add a fuel filter, but I would think if it was clogged it would be stalling under load or going up a hill, not at idle. All the fuel lines have been replaced.

Good thought on the ignition coil, it is the original. The stock Lucas Opus ignition gave up the ghost a long time ago, so it has a Pertronix ignition in it now. I just checked the ignition timing this evening and it's spot on.

Could be an issue with the carb, it has been getting a little finicky starting cold, like it catches but the choke pull off isn't working right so it stalls a few seconds after it catches, so I have to mash the gas to keep it from stalling. A few seconds of running and then it runs perfectly. I think it has been a while since the carb got a repair kit. Last year the screws on the choke valve worked loose and it started leaking gas (the choke is a needle valve, not like your typical choke). I got the alignment marks on the bimetal assembly lined up, but maybe the linkage is sticky.

 

[Wrenchturner44]

Make sure the diaphragms in the carbs are good too. Could have a weak one.

 

[ctrcbob]

Again, not familiar with MG’s however, if the MG Midget uses
SU Carbs (Concentric - Constant Velocity Carbs) don’t forget you MUST add oil after unscrewing the top center bolt to keep the slide operating properly. If you don’t lube SU carbs, the car will run terrible.

 

[NitroM3]

Dave just curious not related but how long you owned you MG?

 

[drtyler]

Stock ‘77 Midget in US would have the 1500 Triumph engine and a single Zenith Stromberg carb. Is this currently the engine/carb in your car?

 

[2EHA]

zenith-stromberg CD carbs operate on the same principle as SUs. extremely crude but they can in fact fuel an engine

 

[Dave Sherman]

Again, not familiar with MG’s however, if the MG Midget uses
SU Carbs (Concentric - Constant Velocity Carbs) don’t forget you MUST add oil after unscrewing the top center bolt to keep the slide operating properly. If you don’t lube SU carbs, the car will run terrible.

Yes, very familiar with the dashpot, had to repair it a while back because the o-ring around the adjusting slug deteriorated and would frequently leak the oil out.

Dave just curious not related but how long you owned you MG?

Bought it from a friend in 2003 after it sat in his garage for 18 years. Carb was rebuilt back then, along with a new electronic ignition, new brake lines, new alternator, battery, brakes, brake lines, master cylinder, etc.. Only 38,000 miles on it so far.

Stock ‘77 Midget in US would have the 1500 Triumph engine and a single Zenith Stromberg carb. Is this currently the engine/carb in your car?

Yes, only the fuel pump was updated.

 

[ka9mnx]

As previously mentioned, coil getting hot and breaking down. Had that issue with my '62 Sprite.

 

[NitroM3]

Ok so my original response still may be a stronger consideration to do and based on your response to me as well to others here you will likely find some interesting things during your cleaning and serving needed gas kits and o-rings .You may be looking at the fuel tank and fuel line at the tank to the carb if they are original for future servicing ?

 

[flanso]

If the rubber carb diaphragm is perforated, air bypasses the throttle valve causing erratic idle.