1977 MG Midget 1500 Problem

[my77midget]

I have a problem with my 1977 MG Midget 1500, and I'm really hoping someone out there has a solution for me. The car will run absolutely perfectly for about 40 minutes, then will studder, stagger, and attempt to die, and, eventually does. Today it just barely got me home. Once it happens, it gets progressively worse. This is the third time it has happened to me, and each time I think I have the problem solved, so I take it on my "test loop", which is about a 45-minute drive, and each of the last three times she has done the same thing. The first time it happened, a mechanic friend towed me back to his garage, and the electric fuel pump was dead. This fuel pump had been replaced over the original by a prior owner. My mechanic blew out the fuel lines, (I had already replaced the fuel tank with a new one, and did it properly) and he ran fuel pump tests. The pump was dead, no doubt about it, so we replaced it. Next day she ran perfect again, for about 40 minutes, then the same thing occurred. I was able to make it home. Did some online forums research (not this forum), and many people seemed to have had the same problem, and said to replace the distributer rotor with the high-quality red one from Moss Motors. I did that. So today, fairly confident I had it solved, did the "loop" again, and again, after about 40 minutes, she was loading up, stumbling, progressively got worse, but I managed to get home again. I know driving it when it's acting up will eventually hurt the car, so.....if anyone can help me, PLEASE!! I'm now thinking coil, electronic ignition, or something other electric. Or could it be fuel? I know these are the worst problems to track down, short of having a mechanic follow me in a truck full of diagnostic testers, etc....I'm fairly savvy on some things, but this one has me stumped! Thanks so much for any and all help! Jeff.

 

[JPSmit]

I had this happen (minus the fuel pump) and discovered that the issue was the intake manifold was a little bit loose - when I started it everything was fine but as the engine warmed up it expanded and created a gap - letting in more air - affecting the mixture and all of a sudden exactly what you describe. There is a very easy test. when it is running poorly take off the air filter and cover half the carb intake. If it pickes up with the air restricted this is likely your problem. Good luck and try the simple things first. Keep us posted.

 

[my77midget]

Hey John- Thanks very much! This is something I never would have thought of! I'm going to try this tomorrow morning, on "the loop"! I really appreciate you taking the time to help me out on this. I will keep you posted!

 

[bobhustead]

A bad coil or condenser will produce the symptoms you describe. Fuel is not likely. Another way to check intake manifold air leak is to rock the manifold while running. Position changes by a loose manifold will vary the running speed.
Bob
Bob

 

[my77midget]

Thanks so much guys, for your replies. John, the intake manifold was on tight, no leakage. So it wasn't that. Thanks again for the suggestion!
Bob, I appreciate your input. I'm in the process of ordering a new coil. This was my train of thought from the start, but my mechanic friend said it wouldn't be that. Once I get the new coil in, I'll update you all on the results. Even though so many bad thoughts are crossing my mind right now about dumping the car through the frustrations of the whole thing, I am determined to hang in there and find this problem!

 

[Glovcol]

I have a problem with my 1977 MG Midget 1500, and I'm really hoping someone out there has a solution for me. The car will run absolutely perfectly for about 40 minutes, then will studder, stagger, and attempt to die, and, eventually does. Today it just barely got me home. Once it happens, it gets progressively worse. This is the third time it has happened to me, and each time I think I have the problem solved, so I take it on my "test loop", which is about a 45-minute drive, and each of the last three times she has done the same thing. The first time it happened, a mechanic friend towed me back to his garage, and the electric fuel pump was dead. This fuel pump had been replaced over the original by a prior owner. My mechanic blew out the fuel lines, (I had already replaced the fuel tank with a new one, and did it properly) and he ran fuel pump tests. The pump was dead, no doubt about it, so we replaced it. Next day she ran perfect again, for about 40 minutes, then the same thing occurred. I was able to make it home. Did some online forums research (not this forum), and many people seemed to have had the same problem, and said to replace the distributer rotor with the high-quality red one from Moss Motors. I did that. So today, fairly confident I had it solved, did the "loop" again, and again, after about 40 minutes, she was loading up, stumbling, progressively got worse, but I managed to get home again. I know driving it when it's acting up will eventually hurt the car, so.....if anyone can help me, PLEASE!! I'm now thinking coil, electronic ignition, or something other electric. Or could it be fuel? I know these are the worst problems to track down, short of having a mechanic follow me in a truck full of diagnostic testers, etc....I'm fairly savvy on some things, but this one has me stumped! Thanks so much for any and all help! Jeff.

After the loss of leaded fuel, I had a similar problem with my frogeye sprite which turned out to be the fuel heating up and causing a vapour lock which disappeared when the engine was turned off, but returned again soon after. I re routed the fuel line away from the carb heat shImelda and all has been well.

 

[my77midget]

Thank you, Glovcol! I will add this to my list of musts, as I continue to forage through the wonders of the MG Midget Motor Maze!
Much appreciated!
Jeff.

 

[ErikL]

Did you find the culprit?
It sounds just like my issue that was a bad coil.
/Erik

 

[dave99]

ZS 150 carb? Check the choke spring. Make sure it’s not broken and engaged. The ZS goes full choke if not set or the spring breaks.