Glad to hear the outcome. Another Datsun back on the road!

Just a follow up to the earlier posts on the power valve problems.

The carb is now together and running again. It is now functioning properly, doing all the right things after running it over the surface plate.

After doing some further on bench testing of problem pieces upon further careful examination it turns out the main body of the carb is warped at the top where the air horn attaches. Quite badly too. By putting a straight edge over it was all to clear that the point where the vacuum ports for the power valve mate were very low. I now believe that this produced a vacuum leak and non functioning power valve.

All of those little "ears" that are cast into the main body that the attaching screws are inserted into have pulled upwards after many years of dismantling and re-assembly.

I have now run it over a surface place and trued it up again so will re-assemble and do some testing again later today to see how it goes.

That is my thinking too.

Before I do that I am going to run the engine with the top of the carb and place a vacuum line between the carb body and the air horn with a vacuum gauge incorporated and see how it performs. After that I will make a judgment as to whether or not the vent hole is to be blocked. At the moment I am inclined to block it.

Yes, I think that is normal, probably is a metered vent (very small hole).
So the procedure is to block that hole.

ddgonzal, thanks for the tips.

I made up a little jig for the valve itself to simulate the situation when fitted in the bowl.

It has a little resevoir on top. On filling the reservoir it remained full. As soon as I hit the pin it started to drain away. So that demonstrates that the valve is good.

As to the plunger I notice it is very dry and suspect that it is sticking/ jamming.Have lubricated it has much better action now.


Oddly, there is a hole drilled into the side of the chamber above the piston that "vents" into the air horn on the secondary side. By pushing the plunger in a little bit to simulate rest position, it is very difficult to draw the plunger up, however if I block that vent hole it draws up well.

I am very surprised to see that "vent". Is this usual? Strikes me as very odd in fact. Any comments?

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It's very common for the Power Valve plunger to stop working. It doesn't matter what the specifications are, if that happens it runs very rich all the time. Either it will go down or it won't.

You can test this by sucking on the plunger port.

Quote:

clyons8,
Thanks for those links.

Lots of useful stuff on there generally about vacuum links generally. However my issue is carb specific as I know the carb runs fine with alternate carb.

I not the use of the vacuum pump. I will need to do something like that with the valve actuator.

At what vacuum level will the valve open? I can't see anything in the specifications section .

Is this of any help?

Vacuum Leaks

Testing

Does anyone know of an effective test in order to determine if a power valve is working or not?

I am aware there are two elements to the power valve system : the valve itself and; the vacuum piston/plunger and spring assembly that operates it.

I have an excessivley rich mixture on a 1400 carb (23/27 venturies) with standard jets. Fuel level in the bowl is OK. Has a performance cam.

I firstly want to see if the valve itself is sealing before I start working on assessing the operation of the vacuum piston and the effect of the cam on the manifold vacuum and whether or not it is kicking in too early etc.

Any tips?