My Z Won't Rev

[olzed]

When you changed spark plugs did you get the plug wires mixed up? Do you know how to check that?

[Captain Obvious]

Haha. It's just that troubleshooting is a whole lot easier if everyone involved is using the same language.

I suggest standardizing on the terminology found in the factory service manual.

I'm not suggesting that everyone pour over every last minute detail of the manual... Just download it, open it, and look at the pretty pictures in the EC (Emissions Control) and EF (Engine Fuel) section.

That way when someone says "I can't tell from that pic what the red outlined thing is connected to." The OP can answer "It's connected to something called the 'servo diaphragm'. I don't know what it does, but I found a pic on EC-11."

Then we can handle the rest... :bulb:

[NCdatsunZ]

How many turns down are your nozzles?

Have you downloaded a copy of the factory service manual yet? You can find them here: XenonS30

Tell you what... If you can provide the name that the service manual calls the round thing with the black tube attached to it that's above your red outlined rod, then I'll tell you all about what it does.

Yes I have an FSM. The thing is called a servo diaphragm and it is used to keep the accelerator from going from full throttle to none at once..... right?

I've triple checked the spark plugs wires. I'm getting a vacuum tester and compression tester today. I redid the float levels, one of them was off by about 2mm. I turned the nozzles down 2 full turns.

Sorry for the "This thingy, that stuff" language. I tried to show pictures because they say a thousand words

[olzed]

A friend had set the firing order on his Z, and had tried for two weeks to get it running.

It was obvious there was a problem. It would run but not rev.

He was going by a drawing in Haynes manual and was counting clockwise around the dizzy instead of anticlockwise.

Funny, he had two paid mechanics couldn't pick up the problem. DOH.

Five minute fix.

[NCdatsunZ]

I borrowed a vacuum gauge. The vacuum advance on the distributor held 12 In.Hg. I followed the line to the nipple on the front carburetor and check the vacuum there and it hovered around 15.This is with the car running. The servo diaphragm doesn't hold any vacuum, nor does the A.B Valve or the control valve. I did use a Haynes manual and I had no idea you were supposed to count counterclockwise.

I went backed and checked the firing order and that all the spark plug wires were connected properly and they were.

Edited January 30, 2013 by NCdatsunZ

[madkaw]

This is good-process of elimination. This helps I narrow down things to give you more specific advice.

Do you have a synchronizer for the carbs?

Get the compression check done.

Timing check too! You need to check timing at idle and at least 2500rpm to make sure your mechanical advance is working.

Make sure you get a voltage check at the battery WITH the car running.

[Captain Obvious]

Yes I have an FSM. The thing is called a servo diaphragm and it is used to keep the accelerator from going from full throttle to none at once..... right?

I redid the float levels, one of them was off by about 2mm. I turned the nozzles down 2 full turns.

That servo diaphragm is part of what they called the "throttle opener system", and it's an emissions control device that works in conjunction with the "control valve". What those two devices do together are hold the throttle open a tiny bit in the event of a very high manifold vacuum. For example, when coasting down a long hill with your foot completely off the gas.

It doesn't matter if you were at full throttle to none. All that matters is that the manifold vacuum is higher then the threshold to open the control valve.

When you are at idle with the hood open, that servo should not move. On pre-74 cars, you might be able to get the throttle opener to move a little if you goose the throttle as you described. The manual describes such a procedure, but I've not tried it myself, so I don't know how pronounced of a movement you would get.

I followed the line to the nipple on the front carburetor and check the vacuum there and it hovered around 15.This is with the car running. The servo diaphragm doesn't hold any vacuum, nor does the A.B Valve or the control valve.

The jury is still out on whether the control valve and servo diaphragm are supposed to hold vacuum or not. And the A.B. valve might not really be a problem either depending on where it's leaking to.

I'm thinking that you should have more than 15 in vacuum at idle though. This is at 800 RPM? I'm thinking that two turns down on your nozzles may not be enough. Without more info, I would suspect you are running lean.

What do the plugs look like?

[madkaw]

Also check the float bowl hoses. Reach under there and make sure the small hose that runs from the float bowl is not kinking in anyway. It will be hard to see so you will just have to feel your way around. I mention this because I ordered some from z therapy and the hoses seemed to want to kink easy -thus shutting off fuel.

[NCdatsunZ]

Ok so I warmed it up this morning and noticed that it would rev up ok with the choke on. But when when I took the choke off, it still died. I pulled the spark plugs out and found that the number 6 spark plug was fouled up with carbon. The rest of them looked burnt except for the number 3 spark plug which was wet. I put in new spark plugs a few days ago.

The Float bowl hoses were not kinked. and I am going to do the compression test later today and will post results.

[NCdatsunZ]

Here are my compression test results.

One:135 Two:135 Three:135 Four:130 Five:120 Six:120

The gauge held pressure on all cylinders.

[Captain Obvious]

If it revs fine with the choke on, but dies without it, that's a pretty clear indication that it wants more fuel. But if you've got a wet plug and others that are carbon fouled, that's an indication that it's getting too much.

Can you post a couple good pics of the engine bay. Maybe someone can spot an issue up in the pics?

[NCdatsunZ]

Can you post a couple good pics of the engine bay. Maybe someone can spot an issue up in the pics?

Here you go. I'd be glad to take more pictures from whatever angles if it helps anyone.

Just some shots in the dark here:

Could the problem be because of timing chain stretch?

Just out of curiosity, what do the different numbers mean in the compression test results? Is it due to improper valve adjustment?