QuestionQUESTION: Hello Barrie,
I've got a 1972 mg midget. Up until a month ago, it ran like a dream. However, since then there has been a problem.
It starts up fine, idles fine as well. However, when I press the accelerator, the engine acts as though it is about to die, in fact once or twice it has died.
In addition, the vacuum gauge shoots over to the extreme right to the "leak/late" indicator. Through the tail pipe, I hear a loud popping sound when I press the accelerator and there is very little pick up, but once I'm in third gear, there aren’t any problems.
If I slowly press the accelerator, then the problem isn’t as bad, but if I depress the petal quickly with force, then the problem is noticeable.
I checked the spark plugs and connections to ensure all cylinders are firing. I basically removed a spark plug wire at a time while the engine is running to see whether there is a difference and there is. Therefore, I don’t think it has to do with the spark plugs.
I'm confused as to what has happened, the only thing I did was add fuel and a bottle of octane booster. I do remember the bottom of the tail pipe rubbing against the sidewalk as I attempted to get from the driveway onto the road.
Any help would be appreciated.
ANSWER: Hi Rico
Sounds like a leak in the exhaust to me. It could be that when you grounded the exhaust it broke the seal between the engine and the exhaust, either at the cylinder head or at the joint where the exhaust manifold clamps to the downpipe. Hard acceleration will allow the engine to move on its mountings, opening the gap. Smooth driving doesn't open the gap.
By the way, if your engine mounting rubbers are soft, this will make things worse. They do go soft or even split apart, so check that they are still hard and not broken.
Also, before you start to take things apart, have you remembered to keep the dashpots full of thin oil? If you forget to top up the carburetter dashpots regularly, this can give similar symptoms.
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QUESTION: Hello Barrie,
Thanks for the response.
I've checked the carbs and added abit more tranny fluid in the dashpots although it wasn't very low.
I also checked the exhaust by having a friend place a cloth over the tailpipe for a few seconds while I checked all the joints and there doesn't seem to be any leaks. There are three joints, the engine to the manifold, manifold (four into one), and the pipe to the muffler.
I took a look at the mounts and they are still firm.
I did notice that when I did press on the accelerator there is a loud hissing sound almost like a "sucking" sound.
I was wondering if you have any other recommendations?
AnswerHi Rico.
If you have done ANYTHING to the engine recently, no matter how trivial, please tell me because it would help to trace the problem.
I assume the spark plugs are all clean, the valve clearances are all correctly set, and the ignition timing is correct. Any of these could cause your problem. My next thought is that you either have a problem with air getting into the intake side of the engine, or you have a sticking inlet valve.
1) I would check that the carburetters are correctly tightened up to the inlet manifold. You could also use a length of hose as a stethoscope to try and find exactly where the hissing sound is coming from.
2) Then I would do a compression test on the engine. The actual readings are not critical, so long as they are all roughly the same (give or take 10 psi).
