The Datsun 1200's A12 is an overhead valve engine
similar to my Toyota Corolla's 4K engine.

Does any Datsun owner here have problems with
their timing chain snapping ? This is because my
Toyota's chain has been rattling for a long time and
is actually long overdue for a replacement. I'm
thinking of having it replaced these few weeks.

I have been getting conflicting opinions from
different mechanics and friends. Some say that
that the short-type double chains in OHV engines
won't ever snap and never need replacing, even
if they make a lot of noise. They add that replacing
the chain in these kind of engines is a big hassle
and is normally only done when the engine is taken
apart at overhaul intervals.

Others say it can snap. Yet others tell me that even if
the chain does not snap, the tensioner may give way,
resulting in the chain flying loose.

Thanks, Ronald.

I'll take out the foil and install a new one
again with the shiny side out. I had done it
at first with the shiny side in.

The mechanic who helped me to wrap it earlier, had
wrapped additional black electrical insulation tape
over the foil, covering the entire rubber fuel line
to keep it in place. I'm wondering if this should
taken out, since the tape might well keep the heat
in rather than out.

Hi again,

This post mentioned wrapping the fuel lines
in aluminium foil with the shiny side to help
reduce vapor lock.

http://shop.store.yahoo.com/coolfj40/vaporlockqa.html



Would this mean that the shiny side should
be facing inwards or outwards ?

I've just wrapped them and am afraid I might have
it facing the wrong way. What might happen if
I did ?

Thanks again.

Might switching to a lower octane fuel
help with vapour lock ?

The "premium" petrols here in Malaysia
are 97 octane, the "regular", 92 octane.

Thanks, Vex. Yes, it may well be vapour lock.

How does one really cure vapour lock ? I've
read about switching over to electric fuel pumps,
but the mechanics over here don't really know
how to handle this kind of modification.

Thanks, Dattodude, Phunkdoktaspok and Maztec.

The basic problem is basically, right after starting
up, the idle speed seems OK. If I drive off the car at
speed, and I don't get held up much by traffic, it will
run fairly well too. However, if I leave it at idle right
after starting, or if I get held up by traffic after some
running, and the temperature gauge starts climbing
towards to the 2/3 or middle position, the erratic idle
starts to come in, with the engine sputtering a bit,
close to dying. It did die off once, but I managed to
start it back, though with the engine sputtering and
struggling to hold idle. I only managed to keep it from
dying again by pulling out the manual choke as a last
resort. I can't really figure out what's wrong, but think
it's the idle circuit in the carburetor.

Yes, I did have the mechanic tighten the manifold
nuts, suspecting a manifold leak too. The head
gasket has just been changed, valves decarbonized,
valve seals replaced and rocker clearances adjusted.
The mechanic is really scratching his head too.
(The mechanics over here aren't particularly skillful,
though.)

The ignition system was the first to be suspected.
I'm using a contact points-triggered electronic ignition
system made from a kit by Dick Smith Electronics,
Australia, originally designed by Silicon Chip magazine.
I tried switching back to the standard points ignition,
but it was the same. The contact points and condenser
have just been changed too.

Initially the vacuum advance pump at the distributor was
causing this rough idle problem too. What happened was
the original pump had given way, and the only replacements available here were generic "Century" brands made in Japan (or so the label said, but I suspect more likely from Taiwan). Well, this pump has a plastic adjuster at the rear for fine timing adjustments. The stock Nippondenso one was very well made and heat durable, but this replacement's adjuster was not, and virtually disintegrated from the heat after a few months. Once this happened, the timing went haywire, since this adjuster was at the end of a tensioner spring indenting against the pump's arm connected to the distributor's plate.
I had to buy another pump, same thing happened after
a few months again, before my brother-in-law finally fashioned
a copper adjuster and screwed it in. The ignition timing
at idle appears to be holding well since then.

The spark plugs, plug leads, ignition coil have all been
replaced. Fuel pump and filter have been changed too.
After the second carburetor change, the problem
appeared to go away after I replaced the mechanical fuel
pump, suspecting it didn't have enough pumping
capacity anymore. It's just over a year since, but I'm
wondering whether this pump is starting to give way too ?
There are lots of Taiwanese parts being passed off as
Japanese ones in Malaysia.

There is a quite a bit of discussion in the forum in the
Toyota Starlet website (www.kp61.net), that the stock
Aisan carburetor is not very well designed and prone
to all kind of rough idle problems, virtually impossible
to correct with the idle mixture and idle speed screws.
The Starlet in the US has the same 1,290 cc, 4K engine
as my Corolla, and basically the same Aisan carburetor.
One owner complained his idle speed varied anywhere
from 700 to 1,000 rpm !

I had also read in the forum of a Suzuki jeep website
(can't really remember the URL), which also comes with
Aisan carburetors, that this is the case too. The owner who
made the post mentioned that the source of this rough
idle problem appeared to be a "power piston" in the idle
circuit. The function of this piston is to enrichen the
mixture during low vacuum conditions, such as idle.
If there are even micro-abrasions in its chamber,
possibly from wear and tear, the piston will behave
erratically, the mixture will become way to rich, and
the engine will likely sputter and die. This owner was
quite innovative - he managed to rebore the chamber
and replate the piston or something, and the idle was
fine after that.

This is one jinxed car, but I'll try checking out for things
like manifold leaks, igntion and fuel pump problems again.

Thanks very much, I will check this out.

I believe the L-series were older engines were
used on the Datsun 1600 SSS, etc ?

I would like to apologize to this forum's
administrators and users if my post seems
out of place here.

I'm from Kuala Lumpur, Malaysia.

I'm a Toyota Corolla "DX" KE70 owner, with a 1,290 cc 4K engine, 1981 model. I have changed the carburetor three times - a used one at first, then two brand new ones. The current new one is still giving endless rough idle problems, and I have read this is common with these problematic Aisan carburetors.

I'm considering changing over to the Datsun 120Y B210's A12 engine's Hitachi carburetor, or perhaps that of the B11 Sunny's , and I wonder if
it can be installed in my engine ?

Thank you.