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MG MGB Technical - vapor lock?

have a 72 MGB GT it was running fine until a couple of weeks ago. Cap for the damper came loose and would not stay screwed down, replace the cap and the car ran god for a day- engine sounded as if it were bogging down no power although I could get up to 50 MPH. pulled the needle on the right Su it appeared bent so replaced. Again ran fine for a day or so(dashpot oil was empty) sitting at idel for approx 15 minutes car was ideling ok- let out clutch in 1st car almost died- pumped accelorator no power engine again bogging down under load. Fuel Filter was replaced at start of poor running. removed hose from fuel filter and vapor came out and then fuel started pumping out(fuel pump was running) re attached and starts running. Live in florida hot do I have a vapor lock problem OR?
RE Dickson

Was the fuel filter empty when you started the pump? If so then you probably have an air leak somewhere in the pump or between the pump and the tank. This allows the fuel to run back down the pipe and empties the filter. It is also possible the pump valves are failing or the diaphragm is at the end of it's life. Any of these can be the cause of poor fuel delivery which could cause the lack of power under load.

Vapour locks are, IMHO, unlikely when the fuel pump is mounted at the rear of the car. Any vapour in the line is quickly forced out through the float chamber vents when the pump starts pushing fuel through the system.

Tony
Tony Oliver

I'd agree that vapour lock is almost impossible on the MGB. Whilst fuel may vapourise in the lines in very hot conditions it should be pushed out by the pump as Tony describes. Fuel would have to be vapourising at the rate of a gallon a minute or more if everything else is correct. Test the delivery system by removing the pipe from a carb and directing it into a container. With the ignition on it should deliver at the very least one Imperial pint per minute, and in practice probably double that, in a continuous series of pulses with negligible bubbles. If it happens again i.e. vapour coming out of the pipe when it is removed from the carb, then fuel, then it can only be a float valve stuck closed.
PaulH Solihull

Paul, Tony,
Thanks for your imput, will check out delivery system as suggested.
Again Thanks
Bob
RE Dickson

I had a similar problem recently. Tried everything. Finally determined that sometime water must have gotten down in the tube of one of the carburetor pistons where the damper goes. The water apparently sat under the oil for a long time and created rust. That rust eventually floated around and jammed the damper piston, causing the carburetor piston to stay up. The car would start fine and run fine but after warming up would not idle right and would not start up until it cooled down. Took the carburetor piston out, poured out the oil and ran a rag down with a screwdriver to rub out the junk ath the bottom. That fixed the problem.
Ted Mack

This thread was discussed between 03/08/2011 and 15/08/2011

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