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MG MGB Technical - leaky su carb

I bought a 74' roadster last fall and haven't really had it on the road. I recently began running the engine to inspect for obvious problems. It runs good but I noticed one of the carbs is wet with gas under the lower cover and it drips a little after idling for about 6-7 minutes. I suppose this is a sign to rebuild the carbs. Is this a common problem?
Brian

I Assume your carb is an HIF-4 (no external float bowl). If this is the case, there's a cover on the bottom which is the base of the float bowl. There's an o-ring in here which may be leaking. Either the cover screws are loose, or the o-ring has had its day.

On the other hand, before you remove it, clean the outside of the carburetor carefully, and fire up the fuel pump. (You don't need to start the motor.) Take a look where it's leaking. Is the leak actually coming from one of the hoses, and just dribbling down the carb? It would be a nice treat if the only problem was a loose hose clamp. Is the leak coming from the overflow (another of the copper pipes on the carb)? Then it could just be that your needle valve is stuck open or float has sunk.

None of these in itself indicates the carburetor is due for rebuilding. But you do need to look a little closer for the source of that leak. Oh, and don't run the motor until you find and fix the leak. Notice where the fuel drips onto?

Matt Kulka

If they are HIFs (float bowl in base of carb not mounted to the side) it's just an O-ring and four screws that seal the base plate. I'd try nipping the screws up as a first step, but have a look to see that the fuel isn't leaking from the overflow higher up, suggesting a float inlet needle is sticking.
Steve Postins

Thanks Matt. Correct, it's an original HIF-4. All of the hoses seem to be dry but I may have missed something. Assuming it's an O-ring, I'm guessing I can remove the bottom cover to replace it without taking the carb off and apart.
Brian

I've always taken the carb off to replace the cover. I've considered doing it in place, with a mirror, as I had to replace an O-ring recently. But it's not hard to take off the carbs, and it gives you a chance to check the condition of the floats and check the float level.

The first time I took the carbs off, I took some really close, clear 35mm photos of the linkage in case I had any questions about putting it back together. But after you've done it twice, it's not hard to remember.

Oh, and an empty soup can makes a marvelous stand to hold the carb upside down. Use the ones just larger than a Campbell's soup can. Like the Healthy Choice or Progresso size. (Do make sure to drain the carb of gas first!)
Matt Kulka

Brian,
I confirm Matt comments: It's far easier to remove the carbs from car to swap the O'ring . And carbs removed, you can too replace the float needle and float adjustements .
Good luck .
Renoiu

Thanks again. I like your suggestions,they make good sense. I'll have to give it a go...
Brian

One more thing. Those baseplates can warp with age. The corners with the screws tighten right up, but the edges go banana shaped and don't seal. Replacement castings are thinner and probably less likely to warping.You can't easily do the usual and flat off on a sheet of glass as there's a locating pin or two sticking up.
Dave
Dave Wellings

This thread was discussed on 24/03/2004

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