I have a prob with my stock 1200. For some reason the spark plugs (2 of them the 1 and 4 pistons) keep fouling up black. The other 2 are fine and are free of any excess fuel burning.

I put a set of new spark plugs on and they fouled up real quick and were running #### within hours or driving. It really lost power and when we pulled the plugs out they were terribly fouled black.

I dont understand why they are fouling bad. The leads are fine points fine everything elerctrical fine. Why would only two pistons be getting such excess fuel?

Thanks in advance for any help!

Have you checked the compression of the cylinders in question.. and valves maybe your inlet valves are not fully closing and are drawing fuel?

Is it dry black or wet oily black?

Its definately dry black so i doubt the head gasket is toast.

I just drove to uni and in 25 minutes i can tell its chocked up again ill have to clean it:P

When did it start? Here's a possible scenario: vacuum leak on 2 & 3 (two separate leaks). To compensate, you adjust the idle mixture richer, which smooths out the idle, but now 1 & 4 are way overrich (2 & 3 are happy though).

Or maybe it's an ignition problem. Check the distributor cap throughly for tracking, and check the cam lobe to ensure the points are opening the same amount on all four lobes.

It pretty much started after i changed the spark plugs and changed the oil. I did nothing else.

I did find heaps of gunk (im assuming ferous oxide) on the inside of the distributor cap on the metal bits. I cleaned them off yesterday.

another possable scenerio is that you could have mixed up#1 and #4 plug wires and they are not firing in the correct order.
or it could be that your cap needs to be replaced because it's leaking electricly

hmm if leads #1 and #4 were swapped the performance wouldnt deteriorate. Usually i would say this would be a comppression problem, ie. somthing stopping one of the valves makeing a clean seal with the head, BUT because it is on 2 cyl..... it should be electric. Although a comp. test could save you a lot of mucking around.

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Hey Low1000, go out and switch your stock A10 # 1 and # 4 spark plug leads, then startup the engine and see if it misfires or not ... I think you'll find that it will.

Now if it was a wasted spark ignition, maybe not (?), but the Datsun ignition doesn't fire twice per cycle like some of the modern ignition systems.