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Engine runs rough

Posted by Suelzle

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Engine runs rough #1
Suelzle Bruce Suelzle Raymond, Alberta, Canada 1958 MG MGA	Posted: July 01, 2012 12:00PM Registered: 3 years ago Posts: 94

When starting the car after sitting for a few minutes after a long run, it stumbles and backfires for a few minutes and then runs just fine again. The car was not overheating and all seemed well. I've checked the float bowls and they are full.

Any Ideas?

-Bruce

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Re: Engine runs rough #2
Bob Agar Robert Agar Green Valley, AZ, USA 1953 MG TD "Myrtle Anne" 1957 MG MGA 1500 Coupe "Miss Scarlett" ~ For Sale ! ~ 1974 MG MGB "The Mistress"	Posted: July 01, 2012 12:14PM Registered: 5 years ago Posts: 1,997

Sounds like that old gremlin, vapor lock. Low boiling point of modern fuels contributes. Gas is likely boiling in the carbs or fuel line. I use about half choke to clear this until the engine smoothes out....or just let it work itself out as you describe.

1974.5 MBG Tourer with Weber 32/36 mod and AC.
1957 MGA 1500 Coupe - Stock and original except paint
1953 MG TD - Original car with no mods

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Re: Engine runs rough #3
neely Gary Neely Heber Springs, Arkansas, USA	Posted: July 01, 2012 12:27PM Registered: 9 years ago Posts: 6,120

Do you have the 4' duct on the drivers side installed in front on the slam panel, and a short piece of 4" behind the panel directed towards the carbs. This may help a little.

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Re: Engine runs rough #4
Suelzle Bruce Suelzle Raymond, Alberta, Canada 1958 MG MGA	Posted: July 01, 2012 12:36PM Registered: 3 years ago Posts: 94

I do have the duct in front of the panel but not behind, I believe a have a short piece left, I'll try adding it to the back side.

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Re: Engine runs rough #5
peter d peter h yorkshire, United Kingdom 1958 MG MGA Coupe 1977 MG MGB "Abomination"	Posted: July 01, 2012 12:58PM Registered: 1 year ago Posts: 699

Hi Bruce
Dont know if this is related,Just looked at the picture of your engine and noticed that the fan blade is on the wrong way (i think)Is it still on that way? Someone may confirm this.Could this cause high temps in the engine bay.

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Re: Engine runs rough #6
Suelzle Bruce Suelzle Raymond, Alberta, Canada 1958 MG MGA	Posted: July 01, 2012 02:01PM Registered: 3 years ago Posts: 94

Hi Peter, Yes that's an old picture, I've since corrected the fan. The engine is running around 190 F when shut off and I do have a good carb shield (non original).

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Re: Engine runs rough #7
Gary E Gary Edwards Kernersville, ,N.C., USA 1962 MG MGA MkII 1974 MG MGB GT	Posted: July 01, 2012 04:14PM Registered: 6 years ago Posts: 5,216

All the MGs I ever owned have done that. After sitting a short while the engine will heat up due to no water circulation. When it gets hot enough it will cause vapor lock as Bob mentioned. The best solution if it bothers you that much is to installed a thermostatically controlled electric fan that will continue to run until the engine cools down. The water will circulate some through convection.

Gary

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Re: Engine runs rough #8
Suelzle Bruce Suelzle Raymond, Alberta, Canada 1958 MG MGA	Posted: July 01, 2012 04:33PM Registered: 3 years ago Posts: 94

Thanks Guys,

Not a big worry for me, but I thought there may be a simple solution

-Bruce

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Re: Engine runs rough #9
barneymg Barney Gaylord Naperville, Illinois, USA 1958 MG MGA "MGA With An Attitude"	Posted: July 02, 2012 03:08AM Registered: 8 years ago Posts: 2,155

There is a simple solution. Open the bonnet and let it vent for 10 minutes after shut down. Maybe not convenient or practical, but real simple, and it works. I used to do that regularly when autocrossing in hot weather.

Barney Gaylord
1958 MGA with an attitude - http://MGAguru.com
Notice: - Do not leave a PM for me on the forum server. Send any private message to my personal e-mail address barneymg@mgaguru.com

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Re: Engine runs rough #10
Suelzle Bruce Suelzle Raymond, Alberta, Canada 1958 MG MGA	Posted: July 02, 2012 12:57PM Registered: 3 years ago Posts: 94

Your right Barney,

As it turns out we just got finished a parade, where of course the car overheated. I parked it with the bonnet up for few minutes, it started and ran just fine.

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Re: Engine runs rough #11
David Pyle TX, USA 1958 MG MGA 1500	Posted: July 02, 2012 04:14PM Registered: 1 year ago Posts: 426

Just H2O and Water Wetter. Not everyone agrees but works for me...plus a shroud and baffle above the radiator. I'm down 15 degrees and it is plenty hot here 95+ everyday.

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