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MG MGA - MGA floods if not started by the first attempt

Hi all, My early MGB powered and carb'd MGA developed a hard starting problem last fall after I reset the needle height in the carbs. Jets were levelled, needles both set in the pistons with just a touch of shoulder showing. Float heights checked and were even a little on the lean side, but I left them. Needles and seats hardly have any miles on them. When I first bought the car it would always start on the first try with some choke and leaving the gas pedal alone. Now it only starts after several tries without any choke and pressing the accelerator lightly and once going it takes a lot of feathering the pedal to keep it running and to finally clear out the cylinders enough to fire on all cylinders. So it's obviously flooding, but I don't understand why. It starts quite easily after being shut off for a while so I don't think it's dumping fuel down into the cylinders after being shut off, although I did notice yesterday after some spirited cornering a smell of fuel and the car started hesitating at higher revs.
Sticky floats, perhaps?
RK knowles

Couple of thoughts - Are you using an after market fuel pump and if so, is the output pressure under 4 psi? If your pump is putting out more than 4 psi (physically impossible with a OEM SU pump), you could be pushing fuel past the needle valves. Is there some debris trapped under the needle valve? This would keep the needle valve from closing off the fuel flow when the float bowls are at the proper level. Finally, are the vent/overflow lines from the float bowls clogged? If they are, air pressure above the fuel level will cause the fuel to be pumped directly into the carburetor jets. Cheers - Dave
David DuBois

Hello RK, are the spark plugs dry or really wet? I had the same problem in France on my way to the Goodwood Revival 2008 with my ZB Magnette!
The spark plugs were dry as there was no fuel in both float chambers, the needle valves were sticking! Of course, this was the last point we had checked after changing contacts, condenser and even the ignition coil! Are the filters blocked with debris? Old fuel contaminated with water?
Good luck!
Dietrich
D. Krahn

I had a similar problem once and it turned out the floats where leaking.
Richard Taylor TD3983

Thanks all, I'm not sure of the car was fitted with an aftermarket fuel pump, but I would bet it's an SU replacement, You'd think if was consistantly flooding then it would be hard to re start after sitting for a while after it's been run, but it's fine. I'm thinking needle valves and seats. The overflow tubes are clear. When I took a quick look at the floats they were fine, no leaks and there was plenty of fuel in the bowls. Needles and seats might be the reason for running crappy after some corners?
RK knowles

As far as I know, the needles should be fitted with the shoulder flush with the piston bottom. The way you have them, ie, proud, would make the setting weaker than intended over the rev range.
A smell of fuel is usually the rubber washers on the stem of the float bowl are leaking. (If the float bowls are not overflowing.)
Could be that your choke cable/levers have gone out of adjustment. There is a great tech article just been posted on the NAMGAR.com web site describing the procedure to get these right.(You have to be a NAMGAR member to access this article).
Peter.
P. Tilbury

This thread was discussed between 06/02/2011 and 08/02/2011

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