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MG MGA - Engine speeds and slows /stops

After head work and re-assembley ( incl. valve stuck problem) etc finally got around to starting the car . I adjusted the SUHif 44 jet and cables as per spec. Started and the engine is totally unstable...winds itself up to 1500 then 2500 with no help from my foot , then runs for a little while never settling and then dies. Loads of fumes from front of manifold.
I presume I have a manifold exhaust leak.....but could it cause that much instability. ..perhaps in combination with an air leak. Any comments ??
I did have some stud and thread problems getting the manifold on.

Have ordered a new set of exhaust studs and long brass nuts for reassembley after I take the judson and manifold off...
Neil Ferguson


Not sure what you're asking but until you get the manifold leaks sorted out you can have all kinds of problems.

Gene Gillam

Gene..sorry about confusion...I was wondering whether a minor manifold leak could cause such engine behaviour....or should I be looking for something else as well..I want to look at things in parallel if necessary as I need to get this car back on the road as I am suffering from MDDD .. ...........Mga Driving Deprivation Depression
Neil Ferguson

Sounds like a bad intake manifold leak.

You have a manifold gasket leak on the inlet side. You probably disturbed the quite small sealing interface on the joint between the carb manifold and the Judson casting. I had the same problem when I installed the Judson, and only when I removed the unit did I find the problem. That is why I always install the entire carb run onto the unit while it is still out of the car- although it is possible to install this when the compressor is in the car, you can't see the sealing surfaces and it is really hard to line up the manifold and threads and not lose the gasket on the way.

It will continue to run away as fast as it can get fuel, until it is starved or running so lean that it dies. If the air leak gets worse the engine will red line, and suck all the marvel oil through in a home made smoke screen that will kill all mosquitoes in the firing line.

I'm afraid it's going probably going to have to come off again, but if you are luck it will rotate on all the hoses and wires to rest on a blanket on the shroud/wing join and give you easy access to the gasket and carb manifold bolts. Practice makes perfect, and it is possible to fit without any skinned knuckles and only moderate swearing!
dominic clancy

Dominic....a thousand thanks...
Neil Ferguson

After a load of email help from Dominic the problem was bottomed. It was a leak through the bottom half of the Judson body to inlet manifold connection.... the gasket was screwed and there is no way to view...a big gap.
All back together ...reatsrted , adjusted idle and set up mix for 3.5% CO and off for a quick drive . Happiness on wheels again...and feels like some umph returned from the top end clean up and seal lap. Judson giving positive pressures again ( new belts ).
Neil Ferguson

Hmmm guess I don't get a gold star.....but I knew it was an intake leak!


Anyway glad your up and running...mayby someday Ill be able to afford a supercharger!

A gold star for your got it in one...Doninic knew exactly where on the Judson manifold blind spot. I am glad I consulted the Delphi oracles on the is it fixed quickly.
Neil Ferguson

Ya.. Doms a good source for definitely helps to have a guiding hand....but you would have eventually got it....what choice did you have!


Well done Neil. Interesting discussion even for us normally aspirated runners.

Steve Gyles

Congrats Neil...they are fun to drive when they're running well!
Gene Gillam

This thread was discussed between 15/06/2016 and 17/06/2016

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