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MG MGB Technical - '74 B Would Not Run When Warm

I had a problem with my '74 B that drove me crazy for a couple of months. The problem started suddenly and the symptoms were always the same. I could start the engine normally (cold start) using the choke. Once the engine began to warm up it would start to run progressively worse until it died. The engine would not start and run normally when warm and any pumping of the accelerator resulted in backfiring through the front carb. The plugs would foul with raw fuel as though the ignition was to weak to provide adequate combustion.
Since I was going to change out the tired old oil burning engine anyway, I went ahead and replaced it with a rebuilt short block. I also replaced all of the ignition bits and pieces (including a rebuilt distributor), the fuel pump and the carb. floats and jets. I figured one or all of those improvements should have solved the problem.
Nope! Same problem.
The only things I had not replaced or rebuilt were the HIF4 starter valves. That was it. The "O" rings were hard as rocks and were letting fuel flood out the engine as it warmed up. I replaced the "O" rings and valve seal and all was well. My '74 now runs like a champ. If you do the same thing to your B, be sure and not over-tighten the nuts that compress the valve seals. The seals will crack and become useless.
Gary Cash

Gary;

Thanks for the post. I had trouble with my HIF4 cold starting valves, however it was a nick in the carb body where the outer gasket seats that caused my grief. I missed it when I rebuilt them doing a dual carb conversion on my 76 B. It would sometimes leak raw fuel and drip off the bottom of the carb after running, then shutting off. After suspecting and inspecting the bottom plate gaskets,and throttle shaft seals, I finally discovered the scource. Took the carbs off, disassembled cold start valve, and reassembled with sparing application of rtv sealant. I know rtv isn't for use in fuel systems, but it is holding up fine since last year.

Pete Haburt
Pete Haburt

This thread was discussed on 16/03/2002

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