Maybe you guys can help.
Here's the thing. No. 3 cylinder is sometimes missing.
Symptoms:
No. 3 starts missing, there's still a spark going to the plug, but the plug
is fouling. Pull it, and it's black and wet.
When it's running on three, it does start to blow a lot of smoke, and STINKS
of petrol.
Clean it up, it works fine. For a while.
Also, the problem is always more persistent on hot days. There's a heat
shield missing between the exhaust manifold and the carbies, and what with
the fuel I'd been running, we thought it might have been a fuel problem, but
been running nothing but optimax through her since, and have just changed
the fuel filter, pulled the carbies apart(no problem - just a leak at the
gasket for no. 3, now fixed).
Compression test shows that all cylinders are at 140psi - apparently a
little lower than standard, but they're all the same! One possibility is
that when the engine was rebuilt (about 5 years ago) pistons from a Datsun H
series engine were put in (exactly the same as from my U series engine, but
with a concave top, instead of a flat top).
Another possibility is that although Nissan factory rings were used, the
engine *is* 30 years old, and maybe needed larger rings. But why is it only
no. 3 that's fouling? And why isn't the compression lower on no. 3? We're
confused, baffled, and I'm tearing my hair out.
Also, there is an aftermarket thermo fan which is pulling lots of current,
maybe the spark just isn't quite enough, at times?
(That's me being hopelessly optimistic, so as not to have to spend mucho
dollars on a rebuild.)
Any ideas on what this problem could be?
Cheers,
Steve
(SR311-01113)
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