Z24 petrol engine in Nissan Urvan *stock carb*

[richURVAN]

Hey folks,

 

The engines stopped idling well . . . I think it first occurred when I pulled out of a gas station with less than quarter of a tank (fuel was way too pricey there), and there was a steep verge which coming down shook the Van a fair bit and I've been thinking maybe some sludge got sucked up from the tank.

 

So I filled up the tank with 98 ron, changed the fuel filter, checked the plugs for soot (they looked good), sprayed a bunch of carb cleaner down the carb and it's still not idling. Runs and revs fine though. Where is the idle control valve on the carb? Only carb I've ever worked on was out of a Briggs and Stratton lawnmower! 

 

There are more YouTube videos on just replacing the stock carb with a Weber 32/36 so I'm more inclined to do that, but if I can turn a screw half a turn and solve it then bingo!

 

Ta,

Rich 

 

 

[datzenmike]

Is the above picture of the engine warmed up?

 

Look for a small vacuum line attached to the intake that fell off in the jolt.

[richURVAN]

22 minutes ago, datzenmike said:

Is the above picture of the engine warmed up?

 

Look for a small vacuum line attached to the intake that fell off in the jolt.

hmm I wouldn't say warmed up been running 5 minutes or so but the temp needle wasn't above quarter that's for sure.

 

Can you see where there should be a vaccum line connected?

 

I just went to my local Repco to buy some Seafoam (Oz equivalent) and the guy behind the desk was only a DIY Datsun mechanic!

 

He said to try swapping over two spark plugs leads and running the engine for 30 seconds coughing and spluttering and might purge the carb a bit.

 

Likely to be sucked up crap and blocking the idle control jet. I'm guessing you got to take the carb off to really get to this and clean it properly.

 

[datzenmike]

Don't be swapping plug wires.

[richURVAN]

38 minutes ago, datzenmike said:

Don't be swapping plug wires.

Not worth a try? Could I damage something permanently? 

 

It's an old school trick apparently . . . 

Edited May 5 by richURVAN

[richURVAN]

4 hours ago, datzenmike said:

Don't be swapping plug wires.

 

didn't work.

 

I found this post from way back on idling . . . 

 

 

can I apply the same checks as your response there? 

 

Its just trickier on this Van cos you can only really access one side of the carb. I may have to take the drivers seat and base plate out, I can't even see any screws to adjust from the visible side. Also how to adjust idle speed screw when engine won't idle at all? Keep screwing in until it doesn't stall when turned on? 

[datzenmike]

If there is blockage in the idle circuit turning the adjustment screw out won't help. The original adjustment wouldn't change so something else.

 

Try this: Have someone turn the ignition on off on off several times. Don't start. YOU listen near the carburetor. You should hear a soft clicking sound. Do you hear anything?

 

 

[richURVAN]

13 hours ago, datzenmike said:

If there is blockage in the idle circuit turning the adjustment screw out won't help. The original adjustment wouldn't change so something else.

 

Try this: Have someone turn the ignition on off on off several times. Don't start. YOU listen near the carburetor. You should hear a soft clicking sound. Do you hear anything?

 

 

Ok mate I'll go and try that now . . . I'm on my own but I'll run a bit of tube to my ear from the back of the carb hopefully should hear something.

 

Can I rule out anything to do with the ignition system like the electric control module, coil, distributor or plug wires since it starts up and runs fine (being only that it wont idle)? 

[richURVAN]

OK I am getting the click from the carb on ignition ON and OFF . . . 

[datzenmike]

Clicking means the idle cut solenoid is working.

 

It's running so not module or coils, cap, rotor or wires and plugs.

 

You could just confirm that both intake and exhaust sides are firing.

 

 

[richURVAN]

51 minutes ago, datzenmike said:

Clicking means the idle cut solenoid is working.

 

It's running so not module or coils, cap, rotor or wires and plugs.

 

You could just confirm that both intake and exhaust sides are firing.

 

 

 

this only has 4 plugs on the intake side

 

I just ran it up to operating temp with a brick on the accelerator and butterfly fully opens once warm.

 

I had a look on the other side of the carb with a mirror and can see two what I assume to be vaccum ports with no hoses which are probably from the EGR delete by PO.

 

I can only see one alloy screw with spring.

 

I'll now take the drivers seat off to get more access.

 

 

 

 

[datzenmike]

Didn't know the Z24 came with single plugs. Our idle screw is set and the screw covered by an aluminum plug so owners can't mess up the mixture. Screw is maybe accessible down there. Still the screw didn't adjust itself magically, still feels like a hose off and vacuum leak. 

[richURVAN]

Ok in my DIY opinion the carb looks shagged . . . completely filthy and all the mechanisms seem pretty loose. 

 

There is one vaccum hose just loose there unconnected . . . and two ports . . . but it looks pretty tight fit.

 

 

[datzenmike]

 

That's the idle mix adjustment screw in the middle.

 

 

That is the vacuum advance and should be connected to the front closest port.

[richURVAN]

10 minutes ago, datzenmike said:

Didn't know the Z24 came with single plugs. Our idle screw is set and the screw covered by an aluminum plug so owners can't mess up the mixture. Screw is maybe accessible down there. Still the screw didn't adjust itself magically, still feels like a hose off and vacuum leak. 

 

Yeah hopefully it's this hose just came off . . . I'll try it on both ports while running and see if it makes a difference . . . then maybe have a play with that screw . . . 

 

Single plug Z24 yeahp here's the proof . . . 

[richURVAN]

Ok the other end of that vaccum hose connects to this unit along with some fuel lines . . . 

 

The pump is in-tank as you can hear it (quite noisey with ignition ON), the fuel filter I changed yesterday is near the tank, what's this? 

 

Very large pressure regulator??

[richURVAN]

45 minutes ago, datzenmike said:

 

That's the idle mix adjustment screw in the middle.

 

 

That is the vacuum advance and should be connected to the front closest port.

 

Ok I re-connected that vacuum pipe and it seemed to fix the problem temporarily . . . idle'd perfectly for 5 mins then started rough again so I had to replace the brick on the accelerator peddle . . . 

 

Now I found another screw to the back nearer the whole throttle cable mechanism which could be the idle control screw? And the other alloy screw is air/fuel mix?

 

I'll try and get a pic of the other screw . . . ok got it . . . 

 

 

[richURVAN]

OK success!

 

I turned what I believe to be the idle speed control screw in just a quarter of a turn and it's now idle'ing nicely (at what RPM I don't know without a gauge), but sounds good though.

 

Now in my desperate state yesterday reaching around the back of the carby i found the other screw (alloy one next to the vaccum ports) and turned it in and out with my fingers who knows how much?? How can I tune this so it doesn't run rich or lean at idle?

 

Second question I have a vacuum hose coming off the distributor which is not connected, I now think this should probably plug into that other vacuum port on the other side of the alloy mixture screw? It's always been disconnected during my ownership though . . . 

[datzenmike]

 

This is the charcoal canister. It stores evaporated petrol fumes from the tank, and releases them into the intake when the engine is running. One hose to the tank for collecting the fumes, one called the purge line to a ported vacuum signal probably the vacuum advance to the distributor and one to the intake to suck in the fumes. When off any evaporated petrol fumes are collected and stored. When engine starts the purge vacuum signal opens the canister to the vacuum line to the intake.

 

 

 

The small hose is likely the vacuum advance hose. The larger one below it might be the canister vacuum hose. Follow it. It should go to the canister.

 

 

 

 

 This screw is probably the idle speed screw. When the engine is fully warmed up and the choke off you can turn the idle up and down with it.

 

 

Idle mixture setting...

Turn the idle down as low as it will run. This makes any mixture changes more noticeable to the ear. Turning the screw in reduces fuel, out increases it. Turn slowly either way. If the idle drops go the other way. What you are looking for is an increase in idle quality and speed. Go slowly enough so the engine has time to respond to any changes. There will be about a half turn where it doesn't change much but quality drops off on either side. Just set roughly in the middle. Presumably the idle speed went up so using the idle speed screw turn it back down. Repeat the in or out turning of the mixture screw to get the best smooth fast idle and turn it down again. This may take 7 or 8 tries to zero in on it. When done you will not be able to improve the idle quality and the idle speed should be around 700-800 RPM. (just guess at it)

[richURVAN]

OK I had a go trying to tune the idle . . . 

 

Ran it up to operating temp and first screwed the idle speed screw in until it starting raising the revs, then backed it off and unscrewed it but it didn't have any effect the other way up until the point I got paranoid about removing it completely and not being able to get it back in.

 

Same happened with the mixture screw, with the idle sounding ok I screwed it in (leaned it out) until it started coughing a bit then went the other way, but 3 full turns out and the screw starting becoming lose as if it were close to falling out. 

 

So I set it somewhere in the middle of running lean and the screw becoming loose.

 

The idle sounds regular to me now and it doesn't smell of fuel or anything.

 

Perhaps I'm missing some subtleties with my ears, I think I'll invest in a vacuum gauge and timing light with tacho. 

[richURVAN]

Also Mike the vaccum hoses . . . 

 

I reconnected the hose from the charcoal canister to the carb here . . . .

 

 

The other port is this where the vacuum hose from the dizzie should plug into? Are they the right way round? 

 

Ta,

Rich

[datzenmike]

Well the Z24 in the 720 truck has the front port to the vacuum advance the other is probably EGR. I don't think it matters really it just opens the purge valve on the canister when the engine is running.

[Sephakrid]

This is a little off topic, but thank you for posting those pictures of your Urvan carburetor. Yours if the first one I've seen (besides mine) that doesn't have a third port for a vacuum line on the side.

[datzenmike]

Ours, the front was vacuum advance. Rear was EGR and the middle one went to the canister purge. On California emissions the rear one was EGR and purge with the middle one going to the vacuum control valve which moderates vacuum advance.

[richURVAN]

22 hours ago, Sephakrid said:

This is a little off topic, but thank you for posting those pictures of your Urvan carburetor. Yours if the first one I've seen (besides mine) that doesn't have a third port for a vacuum line on the side.

 

So the port left of the alloy screw in the picture is for EGR and the one on the right is for charcoal canister or dizzie? My EGR gas been deleted but I have a vacuum hose from the dizzie currently unattached, just the vacuum hose you can currently see which goes to charcoal canister, but that could also be wrong since I reconnected it. 

 

i still can't get the idle right after playing with the screws, think the carb is shagged tbh or in need of a rebuild/replacement, and I think ignition timing needs to be reset since it's still running a bit hot (lean perhaps?) under stress and I'm getting exhaust backfires on deceleration . . .