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Classic/Antique Car Repair/MGB Roadster 1965 starting probs

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Hi Brad, I own a 1965 MGB Roadster, lovely car, runs like a dream for miles. Will always start 1st maybe 2nd time on the key when COLD but not if it's been running for as little as 3 minutes. I can drive o petrol station 2 miles away, stop engine, fill tank, pay, get back in car and it will turn over fine, maybe fire, stall, then it just flips over and over. However if pushed to one side out of way, and then sit there for an hour till she gets cold, hey presto, she'll start on the button and get home. Any ideas why it will not start when warm ??
For your info, all electrics new, new petrol pump, battery and electronic ignition. Unleaded head fitted so it runs on unleaded fuel and so have fitted anti run on valve. New coil, leads etc. Basically, you can drive 100 miles with not a hiccup, but if you turn off ign then you've got to wait ages to start again. Have tried the small choke out a bit and the quarter accelerator, all the usual tricks to no avail. Carbs, by the way original twin S/U, but with new jets. the only thing I can think of which may help would be to fit a Kenlowe rad fan, with thermo switch but having thrown thousands at it over the years, I'm a little reluctant to keep hurling money at it. I've had the car for over 40 years and this has been a recurring problem, but I've always allowed for it, ie leave engine running when buying petrol newspapers etc. It would be lovely to have it working worry free if you've any ideas.
 Thanks in advance
        Rick Appleyard

Answer
It almost sounds like heat soak percolation. That is when the float levels are set a bit on the high side and when you shut down the warm engine the fuel boils and overflows into the intake manifold flooding the engine and hence the no start. However if this is the case it should start when the throttle is held to the floor when the engine is cranking. This is the clear flood start procedure. It could also be that one of the inlet needle valves is not seating correctly.  

Classic/Antique Car Repair

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Brad Sears

Expertise

All automotive including antique and collectible. However if the car has been modified I can only answer in general terms and maybe get you pointed in the right direction.

Experience

Automotive tech instructor. Syndicated auto columnist 1970's though the early 1990's. Syndicated auto radio talk show, Ask Brad About cars, CBS Radio 70's through 90's TV Show "Last Chance Garage" 1980's PBS-TV syndicated. Auto instructor for the following companies: Fram Autolyte Holly Carter AMF Ford Motor University Of Conn Blue Hills Technical School Sugar River Technical Center Grew up in a family garage in Needham Mass and turned wrenches from the age of 14.

Publications
Manchester Union Leader, Nashua Telegraph, Motor Service Magazine, Yankee Magazine, Popular Mechanics (Saturday Mechanic early 80's), Los Angeles Times, New York Times, and lots more.

Education/Credentials
More than I care to remember. Basically Franklin Technical Institute in Boston, Northeastern University, Fitchburg State Teachers College, Tufts University, and a lot of factory schools along the way.

Awards and Honors
Moto Award winner. And much more.

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