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MG MGA - Vapor Lock

I often experience vapor lock with my 62 Mark II. Always after driving for a long while, park the car for five minutes, buy gas and/or a beverage, get back in the car and *sputter* lurch, etc. for a minute while the vapor lock -- or whatever you call it -- subsides. I remember my old 1954 Chrysler Hemi did the same thing and I wrapped aluminum foil around the carb fuel line. Helped but didn't solve it entirely.

The other day after driving for 12 hours/400 miles I experienced the sputter at high speeds while hill-climbing. Like there wasn't enough gas to get through to the motor. Slowing down (to 60mph) solved the problem. It was too cool outside to be heat-related vapor lock (55 degrees, normal engine temp) so I'm wondering if I should flush the fuel lines? Or fuel pump starting to fail? Any suggestions?

thanks in advance...
Jim Paul

Try cleaning out the filters in the banjos at the carbs, and clean the filter in the fuel pump
dominic clancy

Jim, I had the same problem with my '58 roadster. It was especially bad returning home from GT-28. The PO had put basic plain rubber fuel hoses at the fuel line connections in the engine bay & between the carbs. These hoses pass closely enough to the exhaust manifold to create enough heat for vapor lock to occur anytime. I decided to replace the hoses with the stainless braided type hoses and have not had a problem since.

However, you stated that slowing down reduced the problem in which case I would also agree with Dominic that you could have a filter issue especially if you already have the stainless hoses.

Clayton
C. Merchant

Jim:

Re: the vapor lock, you might be interested in Barney Gaylords site www.MGAguru.com and see his index for CB-202 intake-exhaust heat shield
J. Hudrlik

Jim - Since the fuel pump on the MGAs is located inthe back, the fuel is under pressure all the way to the float bowls, which should (note I said should) preclude vapor locking in the fuel lines. Carry a small squirt bottle of water with you and the next time the problem arises, dribble some water on the arm from the bottom of the float bowl to the bottom of the carburetor body and see if that cures the problem temporarily. I had a problem with a TD vapor locking in that area, building up enough pressure to keep the float hard against the needle valve. A set of heat shields cured the problem in the TD, but since the MGA already has a heat shield, you may have to try something else to reduce the engine compartment temperature. Good luck - Dave
David DuBois

Jim; I would suspect your floats and needle valves.I have found that "Gross" brand needle valves don't hang up like the OEM needle valves do. Check the floats for gas inside them, check for wear on the pivot pins and float bearing area and check the float height. Good Luck, Bill
w.g cook

Jim,

I had a similar experience a long time ago. I went to a local racing supply shop and bought a roll of a heat resistant material used in racing and wrapped the exhaust manifold in that. No worries since. BTW -- my heat shield is not original but a very thin MOSS replacement part. Again it is also old, don't know what they look like now.

HTH,
Christopher
christopher wilson

Hi Folks. I used to have a considerable problem with vapour lock. When I looked at the old manifold heat shield, I suspected the problem was occurring or being exacerbated because of the rusty/dirty old heat shield. When new, the heat shield is probably shiny metal, and presumably reflects much of the exhaust manifold heat away from the carbs. When the heat shields get dirty and rusty they likely do not reflect the heat as efficiently, and in fact probably ABSORB exhaust manifold heat because of the dark colour. So a friend bent up a new heat shield from sheet stainless steel material. I riveted the asbestos material from the old heat shields onto the newly fabricated stainless steel shield. The vapour lock problems now seems to be completely gone, although the really hot weather has not arrived in Ontario Canada yet. But there has been no vapour lock problems so far, since the new heat shield was installed. Cheers! GLenn
Glenn

Jim
Your high speed hill climbing sputtering is not vapour lock as you have a good flow of air and loads of cool fuel passing through the carbs.

If it was perhaps running on two cylinders, suspect some form of blockage in the fuel line or the pump may for example, be a cheap type not up to the job or just perhaps failing.

When climbing hills you will be using a lot of throttle / fuel. If there is a lack of flow, and the carbs don't get enough, the front carb will suffer first.

The rear carbie is fed first and maybe using all the available flow and may not leave any or enough to pass on to the front one. Going up hill doesn't help here either. So, not fuel in front carbie - no cylinders 1 & 2 !

Slowing down let's enough into front carbie for all four to fire OK.

Have experienced this - in this case a new pump and correct size pipe from tank to pump cured the problem.
Pete
Pete Tipping

This thread was discussed between 11/05/2005 and 13/05/2005

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