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MG MGB Technical - weird problem at high speed

Hi!
I'm just back from a 350 miles trip with my B GT, it was my first long ride...But I got some trouble..
first, I left very early in the morning, the humidity was high and the temperature about 10-15°C...so it ran perfectly on the highway at about 65 miles/h for about an hour then I started to loose power and the engine was missing..I pulled on the side and open the hood, the carbs were frosted! I had a carburator icing problem..
so I let them warm and go back on the highway..it lasted for less than 15 minutes and the problem reappeared..

anyway, I reached my destination, but on the come back, the temperature outside was much higher, about 30°C..and I had the same symptom, but this time the carbs were totaly hot..

Not the car runs perfectly under 50-55 miles/h, higher than that, it's intermitant, sometime it works great, sometime it starts to die, or miss..I don't know, it looks like a fuel starvation..
it's worst when I climb a hill..
it's only on the forth gear, I tried to run at a high RPM (3500 RPM) on the second or third gear and I didn't get the trouble..

sometime, don't ask me why, it can works perfectly for 15-30 minutes then it come back..

I did a full rebuilt of the carbs few months ago, I did about 1000 miles since that and never got that trouble.
The plugs, rotor, cap and spark plug cables are new...

any idea?
fuel pump issue? vaport lock? It seems to be worst when I open the throtle butterfly..like when you climb a hill..
anyway
thanks in advance for the help..
JF
JF

It might be that the fuel pump can't quite keep up, or it could be an ignition problem that only appears when the engine is hot. Could it be a dodgy condenser?
Miles Banister

This thread was discussed on 09/06/2003

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