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MG MGA - Vapor Lock

I have heard and read about how prevalent these cars are to vapor lock. However I am surprised at how bad it gets! My 58 starts and runs great, operating nicely at 160 degrees. But as soon as it gets warmed up, I can forget about getting it started again until it cools down. I also find that after it is hot it start coughing at low RPM's. My question: Is this Normal? (Grant you it has been 94 degrees here in the northeast of the states.)
Also: Does anybody have any feedback to the devices listed in Barney’s site? (This would be the Intake Manifold shield that minimizes the vapor lock)
Bill R

Bill
I assume that you anyway have the original plate between the exhaust manifold and the carbs? This should have the asbestos side to the exhaust manifold.
You should also have the air ducting from the area behind the grill as this gets cooler air to the carbs.

I would say that only at really high temperature has vapour locking been a problem and this only when I have been in traffic for a good while. It has never affected starting.
Usually it clears when I have run for about 30 seconds after getting out of traffic.

Check ignition timing and fuel to ensure you are not getting the engine hotter than necessary by being badly set up.

After that I am out of ideas but I don't think you should need to resort to bolt-on bits.
I however did hear of someone fitting a small fan to the outlets in the bonnet surround which sounded quite a nice idea. They said that they where otherwise quite useless due to the poor aerodynamics when running at any speed!!

Hope that helps

Neil
Neil Purves

Hi Bill. This is my belief: When the heat shields get old, and rusty the darker colour absorbs engine heat, causing vapour lock. My own MGA was vapour locking on a regular basis. The vapour lock problem all but disappeared when I made a new heat shield out of shiny stainless steel. I re used the old asbestos pads from my old shield. I believe the shiny metal reflects heat away from the carbs, effectively reducing vapour lock.
Glenn

The most common problem we see at the shop is often misdiagnosed as vapor lock but is usually due to either too high a float height or a sinking/sunk float. In either case, the fuel level in the float bowls gets too high and when the engine is shut off, the fuel dribbles out of the jet and into the manifold. Upon restarting the car is way too rich and will either start hard or flood.

Sometimes this happens when the carbs are set too rich, which is also fairly common. With the carb dampers/pistons off, the jets should be nearly level or slightly below the bridge. If they are more than 1/8" below the bridge, something isn't right (idle mixture, needles, general state of tune, something).

As mentioned above, if the heat sheild is bad or missing, you'll sometime boil gas out, but we usually find the two other problems.

Of course, this all assumes that the ignition system is in good condition--make sure you've got 60 degrees dwell and that you're at around 15-20 degrees BTDC at idle (vac disconnected). Weak or poorly timed spark always makes starting harder.

--Carl
Carl Heideman

Glenn, I guess I'll find out what effect color has on it. I just cleaned my heatshield up and painted it engine enamel black.
Wray

On a hot day, maybe take a spray bottle of water along with you just in case the float bowls or metal fuel lines need a bit of cooling off. I haven't tried it yet, but it sounds like a good idea.
Tom

This thread was discussed between 30/07/2007 and 31/07/2007

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