We just bought a 71 squareback . Initially it ran fine but now ......if it starts ..... it will run rough and then eventually die . It will turn over , carbs are getting fuel , and the coil is showing spark when grounded . I have changed the plugs . One showed black and the others were normal . I also changed the fuel filter(s) . The engine has 400 miles on it since the build . Could it be water in the gas causing this issue ?  Any help would be appreciated .

Thanks,
James

You said one plug was black... like dry black (rich fuel) or wet black (oil)?

Air, spark and gas. Needs all three to run. I would eliminated the spark at each plug first to make sure that you are getting spark at the cylinders. Check the points in the distributor since those can close up.  If that doesn't work, then check the carb. It might be bad gas. If it you think it has water in it, replace the gas and try.

I think the godfather once said that 99% of carb problems are electrical, so check the points, set the timing. While you are at it, adjust the valves. A complete tune up should fix it all.

The distributor is a pointless type .

Who do you guys recommend to work on this car ? I'm a mechanical person but VW's are new to me .

Thanks for the advice 39 horses . I will check the floats . That did occur to me that they might be stuck .

One plug is dry/fuel fouled?

I would be guessing something more along the lines of an ignition miss, just building up gas on that cylinder, maybe a bad plug wire, sumthin.  A carb problem would present itself to all four cylinders... they don't discriminate.   

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I must be slipping. You have 2 carbs right ?  Aftermarket I take it seeing how your car had fuel injection originally . Some problems I've had with twin aftermarket carbs was the fact they can have a vacuum leak between the cly.head and the carb base/manifold from poor gaskets(common), just loose to the head, warped base( cupped).  Leaking like that can something cause the problem you are having. If you can keep running long enough ,you can try spraying some WD-40 around the carb  base and see if the idle changes.  I'm not going to tell to use carb spray cleaner. It can be dangerous Let me know

I know some one who had set more than one engine compartment on fire using carb spray to find a vacuum leak when the car backfires or you have a bad spark plug wire arcing to the engine block,  bye bye eyebrows and wiring harness